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Purpose In order to introduce the concept of diagnostic reference levels (DRLs) in the national nuclear medicine practice a survey was proposed and completed through all nuclear medicine departments in Croatia. An additional aim was to increase the awareness of importance and full implementation of a comprehensive quality program that includes devices used in the nuclear medicine chain. Methods Data were collected for more than 30 nuclear medicine single photon emission procedures. National DRLs (NDRLs) as administered activity and also as administered activity per unit mass were calculated in accordance to International Commission on Radiological Protection (ICRP) recommendations. Additionally, effective doses were estimated using conversion factors published by the ICRP. Results NDRLs for nuclear medicine single photon emission procedures were proposed. For procedures performed in only one department typical values were presented as reference. Effective doses related to applied radiopharmaceuticals were calculated to estimate radiation risk related to respective nuclear medicine procedure in more detail. Conclusion This work presents results of the first national survey on DRLs of nuclear medicine single photon emission procedures and proposes reliable NDRLs that represent an actual status of nuclear medicine practice in Croatia. Results have motivated departments to introduce and set their own typical values to be used, as one of the tools, for further optimization process. One of the drawbacks of the DRL concept in nuclear medicine is the lack of the image quality parameters involved. For this reason, a quantity that considers both radiation protection and image quality should be introduced.

Introduction Advanced, Monte Carlo (MC) based dose calculation algorithms, determine absorbed dose as dose to medium-in-medium (D m,m) or dose to water-in-medium (D w,m). Some earlier studies identified the differences in the absorbed doses related to the calculation mode, especially in the bone density equivalent (BDE) media. Since the calculation algorithms built in the treatment planning systems (TPS) should be dosimetrically verified before their use, we analyzed dose differences between two calculation modes for the Elekta Monaco TPS. We compared them with experimentally determined values, aiming to define a supplement to the existing TPS verification methodology. Materials and methods In our study, we used a 6 MV photon beam from a linear accelerator. To evaluate the accuracy of the TPS calculation approaches, measurements with a Farmer type chamber in a semi-anthropomorphic phantom were compared to those obtained by two calculation options. The comparison was made for three parts of the phantom having different densities, with a focus on the BDE part. Results Measured and calculated doses were in agreement for water and lung equivalent density materials, regardless of the calculation mode. However, in the BDE part of the phantom, mean dose differences between the calculation options ranged from 5.7 to 8.3%, depending on the method used. In the BDE part of the phantom, neither of the two calculation options were consistent with experimentally determined absorbed doses. Conclusions Based on our findings, we proposed a supplement to the current methodology for the verification of commercial MC based TPS by performing additional measurements in BDE material.

Background Virtual monoenergetic (VM) dual-energy computed tomography (DE-CT) enables grey-to-white matter contrast-to-noise ratio optimization, potentially increasing ischaemic brain oedema visibility. The aim of this study was to compare the diagnostic accuracy of VM and standard DE-CT reconstructions for early stroke detection. Methods Consecutive patients with non-contrast DE-CT of the brain scanned within 12 h of stroke symptom onset were prospectively included in the study. Patients with other significant brain pathology were excluded. Two radiologists jointly evaluated standard and VM reconstructions (from 40 to 190 keV at increments of 10 keV) for early stroke signs on a four-point Likert scale: (a) stroke definitely present, (b) stroke probably present, (c) probably no stroke, and (d) definitely no stroke. Follow-up imaging and clinical data served as the standard of reference. Diagnostic accuracy was evaluated by receiver operating characteristic analysis. Results Stroke incidence among 184 patients was 76%. In 64 patients follow-up imaging served as the standard of reference: ischemic brain oedema detection was significantly more accurate on VM reconstructions at 80 keV compared with standard DE-CT reconstructions (area under the curve (AUC) = 0.821 vs. AUC = 0.672, p = 0.002). The difference was most prominent within the first 3 h after symptom onset (at 11%, AUC = 0.819 vs. AUC = 0.709, p = 0.17) and in patients with National Institutes of Health Stroke Scale above 16 (at 37.5%, AUC = 1 vs. AUC = 0.625, p = 0.14). Conclusion VM DE-CT reconstructions at 80 keV appear to be the optimal non-contrast CT technique for diagnosing early ischaemic stroke, particularly within the first 3 h after symptom onset and in severely ill patients.

The most accurate absorbed dose calculation in radiation oncology nowadays is provided by Monte Carlo (MC) based algorithms. Such algorithms inherently calculate absorbed dose to medium in medium Dm, m. They can also provide data as absorbed dose to water in medium Dw, m by conversion based on SpencerAttix extension of Bragg-Gray small cavity theory. These two absorbed dose concepts do not necessarily provide similar results, which is particularly prominent in bone structures. Monte Carlo based algorithms used in radiation oncology use several approximations and simplifications to speed up calculation time. Furthermore, they do not use data of chemical composition of media which is the case with generalised MC particle transport simulation algorithms (e.g. MCNP, EGS, GEANT…). Therefore, an investigation of the material chemical composition impact on calculation accuracy was performed comparing calculations obtained using Monte Carlo N-Particle code® (MCNP) and a clinical MC based algorithm. Absorbed dose data acquired by MCNP was used as reference data. Investigation of absorbed dose calculation accuracy was performed for 6MV X-ray beam (Siemens Oncor Expression linear accelerator) in various geometries of different complexities. Comparison between two MCTPS dose calculation options and MCNP calculations in simple (homogeneous) and different heterogeneous geometries was performed using 13 different materials with mass densities ranging from 0.2 g/cm3 to 2.17 g/cm3 (Table 1). The MCNP calculations were performed by assigning material chemical composition and mass density (MCNPMEDIUM). The absorbed dose was calculated as Dm, m. The Dm, m calculation shows very good agreement with standard MCNP calculations except for low- density medium. Therefore, the improvement of the accuracy of MCTPS Dm, m calculation option in low- density medium may be the further step of the research. Nevertheless, the results obtained in this work indicate that Dm, m could be regarded as the preferable dose calculation option.

Objective: To present results of the first national survey on reference levels of CT imaging performed for the treatment planning purposes in radiation oncology in Croatia. Methods: Data for CT protocols of five anatomical regions including head, head and neck, pelvis, breast, and thorax were collected at eight radiation oncology departments in Croatia. Data included volume CT dose index(CTDIvol), dose-length product (DLP), scan length and set of acquisition and reconstruction parameters. Data on a total of 600 patients were collected. Median values of scan length, DLP and CTDIvol were calculated for each acquisition protocol. Third quartiles of the median CTDIvol and DLP values were proposed as the national radiotherapy planning reference levels (RPRL). Results: The largest CoV were assessed for RT Breast (63.8% for CTDIvol), RT Thorax (79.7% for DLP) and RT H&N (21.2% for scan length). RT Head had the lowest CoV for CTDIvol (1, 9%) and DLP (17, 2%), while RT Breast had the lowest coefficient of variation for scan length (12.8%). Proposed national RPRLs are: for RT Head CTDIvol16cm = 62 mGy and DLP16cm = 1738 mGy.cm ; for RT H&N CTDIvol16cm = 35 mGy and DLP16cm = 1444 mGy.cm ; for RT Breast CTDIvol32cm = 16 mGy and DLP32cm = 731 mGy.cm ; for RT Thorax CTDIvol32cm = 17 mGy and DLP32cm = 865 mGy.cm ; for RT Pelvis CTDIvol32cm = 20 mGy and DLP32cm = 1133 mGy.cm. Conclusions: Results of this study show variations in CT imaging for treatment planning practice at the national level which call for optimization of procedures.

Background: Study determines differences in calculated dose distributions for Non-Small Cell Lung Carcinoma (NSCLC) patients. NSCLC cases were investigated, NSCLC being the most common lung cancer treated by radiotherapy in our clinical practice. Materials and methods: A retrospective study of 15 NSCLC patient dose distributions originally calculated using standard superposition (SS) and recalculated using collapsed cone (CC) and Monte Carlo (MC) based algorithm expressed as dose to medium in medium (MCDm) and dose to water in medium (MCDw, ) was performed so that prescribed dose covers at least 99% of the gross target volume (GTV). Statistical analysis was performed for differences of conformity index (CI), heterogeneity index (HI), gradient index (GI), dose delivered to 2% of the volume (D2%), mean dose (Dmean) and percentage of volumes covered by prescribed dose (V70Gy). For organs at risk (OARs), Dmean and percentage of volume receiving 20 Gy and 5Gy (V20Gy, V5Gy) were analysed. Results: Statistically significant difference for GTVs was observed between MCDw and SS algorithm in mean dose only. For planning target volumes (PTVs), statistically significant differences were observed in prescribed dose coverage for CC, MCDm and MCDw. The differences in mean CI value for the CC algorithm and mean HI value for MCDm and MCDw were statistically significant. There is a statistically significant difference in the number of MUs for MCDm and MCDw compared to SS. Conclusion: All investigated algorithms succeed in managing the restrictive conditions of the clinical goals. This study shows the drawbacks of the CC algorithm compared to other algorithms used.

Introduction Early breast cancer detection can be achieved by enforcing the quality of mammography screening program. Hence, proper breast positioning is necessary. Systematic education of radiographers on mammographic positioning is a prerequisite for obtaining high-quality mammograms. The aim of this study is to demonstrate the importance of self-evaluation and education of radiographers involved in a breast cancer screening program. Methods The First School of Mammographic Positioning was organized in 2018 at Clinical Hospital Center (CHC) Rijeka and 24 radiographers included in the screening program attended. Four months after the School, an analysis and comparison of randomly selected mammograms was performed. Retrospective analysis was performed, and two sets of collected data were gathered from the period before and after the education. The quality criteria for evaluation were set and the mammograms were independently analyzed by two radiographers with experience in mammography. The chi-square test was used to perform statistical analysis. Results Results showed a statistically significant difference in the quality of mammograms before and after training for all criteria (p Conclusion Self-evaluation and education of radiographers at the CHC Rijeka have led to a significant progress in image quality. Implications for practice Results of this work imply that there is a strong need to formalize breast imaging education and the need to implement systematic education at the national level in Croatia.

Due to their small size, numerous cellular divisions of the still growing and developing tissues and organs, as well as a longer life expectancy, children are approximately three times more sensitive to the same doses of ionizing radiation than adults. This is especially the case with the computerized tomography (CT) examinations, which despite making only 17 % of the ionizing radiological examinations, account for as much as 49 % of the total patient irradiation. Because of this, the Image Gently campaign in the early 2010s was thinking about abandoning the CT examinations in pediatric radiology and replacing them with the ultrasound or magnetic resonance imaging as the methods of choice. The appearance of Flash CT technology, which simultaneously shortens the recording time and reduces radiation doses, has led to the abandonment of this way of thinking. This is also supported by the fact that, on the one hand, CT examinations are practically irreplaceable in the cases of trauma, while on the other hand, children, as well as members of all the other age groups, are constantly exposed to a smaller or larger amount of the environmental ionizing radiation (Earth, space, airplanes). In this sense, it is increasingly recommended to use the low dose CT (LDCT) techniques individually adapted to each patient, due to their small amount of ionizing radiation. On this track, we have tried to make a review of the latest findings on the mentioned problem based on the scientific papers published over the past three years (2016-2018). They show that the CT examinations are not only abandoned in the pediatric radiology, but that on the contrary, in the cases of numerous indications LDCT examinations make the gold standard.

Introduction: Within the past two decades, we made significant progress in radiation therapy for prostate cancer. At UH Rijeka IMRT became the technique of choice for radiation therapy following radical prostatectomy since 2016. Previously, an advanced 3-DCRT technique using the field-in-field (FiF) method was used for dose distribution optimization around target volumes and organs-at-risk. This research has been performed to investigate the influence of planning technique choice (FiF or IMRT) on coverage of target volumes with prescribed dose and organs-at-risk sparing. Materials and methods: Comparison of dose distributions calculated using FiF and IMRT techniques was performed retrospectively for ten patients who underwent postoperative radiotherapy. The prescribed dose for all patients was delivered using IMRT, and for this research, we also calculated dose distributions using the FiF technique. For FiF and IMRT techniques, we used linear accelerator photon beams. To determine the influence of planning technique on dose distribution parameters related to target volumes (GTV, CTV, PTV1, PTV2) were analyzed. For organs-at-risk sparing evaluation (rectum, bladder, femoral heads), we used dose-volume constraints. Results and discussion: The analysis of parameters related to target volumes has shown that most of them had no statistically significant difference (V100%(GTV), V100%(CTV), V95%(PTV2), V95%(PTV1)). For both planning techniques, internationally set dose constraints were achieved. Statistically, we found a significant difference for V100%(PTV2), p=0,000534, and V100%(PTV1), p=0,042944 in favor of IMRT. A statistically significant difference (p=0,045966) was found for the volume of the rectum, which receives 40Gy, and for the volume of femoral heads, which receives 30Gy (p=0,000385), where the sparing is better for IMRT. For dose-volume constraints related to the bladder, no statistically significant differences were found. Conclusion: Results of this research show a statistically significant difference for V100% target volume coverage for PTV1 and PTV2, with better dose coverage accomplished by IMRT. Concerning organs-at-risk sparing, a statistically significant difference in favor of IMRT was found for rectum volume, which receives 40Gy. Expectedly, IMRT was superior to the FiF technique. However, differences between the two planning techniques were relatively small, which points to the fact that the FiF technique is viable as a technique of choice., Uvod: U posljedna dva desetljeća, u liječenju raka prostate radioterapijom postignut je veliki napredak. U KBC-u Rijeka, od 2016., jakosno modulirana radioterapija (IMRT) postaje tehnika izbora kod radioterapije operiranog raka prostate. Do tada je tehnika izbora bila napredna 3D konformalna radioterapija (3DCRT) korištenjem tehnike „polja u polju” (FiF). Istraživanje je provedeno s ciljem ispitivanja utjecaja izbora tehnike planiranja (FiF ili IMRT) na doznu pokrivenost ciljnih volumena i poštedu organa rizika. Metode i materijali: Usporedba raspodjela doze izračunate koristeći FiF i IMRT retrospektivno je učinjena kod deset bolesnika kojima je indicirana postoperativna radioterapija. Svim je bolesnicima predana propisana doza IMRT tehnikom, a za potrebe ovog istraživanja izračunate su i raspodjele doze FiF tehnikom. Da bi se utvrdilo utječe li tehnika planiranja na raspodjelu doze, analizirani su parametri važni za ciljne volumene (GTV, CTV, PTV1, PTV2), a kod analize poštede organa rizika (rektum, mokraćni mjehur i glavice femura) korištena su dozno-volumna ograničenja. Rezultati i diskusija: Analizom parametara vezanih za ciljne volumene utvrđeno je da kod većine (V100%(GTV), V100%(CTV), V95%(PTV2), V95%(PTV1) nema statistički značajne razlike. Kod obje tehnike postignuta su dozna ograničenja propisana međunarodnim smjernicama. Statistički značajna razlika utvrđena je kod V100%(PTV2), p=0,000534 i V100%(PTV1), p=0,042944 u prilog korištenja IMRT tehnike. Utvrđena je statistički značajna razlika (p=0,045966) za volumen rektuma koji prima 40Gy, kao i za volumen glavica femura koji prime apsorbiranu dozu 30Gy. U oba slučaja pošteda organa rizika bolja je korištenjem IMRT tehnike. Za promatrana dozno-volumna ograničenja vezana uz mokraćni mjehur nije utvrđena statistički značajna razlika. Zaključak: Rezultati istraživanja pokazuju statistički značajnu razlikukod usporedbe volumena kojemu je predana propisana apsorbirana doza (V100%) za PTV1 i PTV2, tako da je bolja dozna pokrivenost kod IMRT tehnike. Pri poštedi organa rizika statistički značajna razlika u korist IMRT-a utvrđena je kod analize volumena rektuma kojem je predana apsorbirana doza od 40Gy i volumena glavica femura kojima je predana apsorbirana doza od 30Gy. Prema očekivanju, IMRT daje bolje rezultate. Međutim, razlike u analiziranim parametrima između dvije tehnike planiranja (FiF ili IMRT) kod većine analiziranih parametara nisu statistički značajne što upućuje da kvalitetno planirana radioterapija FiF tehnikom može također biti tehnika izbora.

Prema članku 33. Zakona o radiološkoj i nuklearnoj sigurnosti (NN 141/13, 39/15, 130/17, 118/18) te člancima 14., 15. i 16. Pravilnika o uvjetima i mjerama zaštite od ionizirajućeg zračenja za obavljanje djelatnosti s izvorima ionizirajućeg zračenja (NN 53/18), radiološki odjeli u Hrvatskoj koji provode dijagnostičke i intervencijske postupke u medicini upotrebom ionizirajućeg zračenja, obvezni su provoditi program osiguranja i kontrole kvalitete električnih uređaja koji proizvode ionizirajuće zračenje. Parametri koji moraju biti mjereni definirani su u Prilozima 3. do 12. koji su sastavni dio Pravilnika o uvjetima i mjerama zaštite od ionizirajućeg zračenja za obavljanje djelatnosti s izvorima ionizirajućeg zračenja (NN 53/18). U Klinici za infektivne bolesti „Dr. Fran Mihaljević” u Zagrebu dnevne testove provode radiološki tehnolozi, dok složenije procedure mjesečno i godišnje provode medicinski fizičari. Tijekom provođenja testova kontrole kvalitete, upotrebljava se različita oprema za evaluaciju parametara uređaja. U slučaju odstupanja od preporučenih rezultata, moraju se poduzeti korektivne mjere kako bi se ispravila odstupanja. Sve procedure moraju biti pohranjene, a izvješća upućena kompetentnim osobama i institucijama. Cilj je ovog rada prikazati multidisciplinarni pristup u provođenju programa kontrole kvalitete uređaja za kompjutoriziranu tomografiju u Klinici za infektivne bolesti „Dr. Fran Mihaljević” u Zagrebu od ožujka do rujna 2018. godine. Multidisciplinarni tim sastojao se od radioloških tehnologa i radiologa iz Klinike za infektivne bolesti „Dr. Fran Mihaljević” u Zagrebu, studenata radiološke tehnologije Zdravstvenog veleučilišta u Zagrebu i medicinskih fizičara iz Kliničkog bolničkog centra u Rijeci. Fizičari savjetuju radiološke tehnologe o tehničkim poboljšanjima kako bi postigli najbolje rezultate u provođenju svakodnevnih procedura kontrole kvalitete. Svi testirani parametri bili su u granicama prihvatljivosti, osim detekcije prstenastih artefakata. Da bi se otklonili prstenasti artefakti, pročelnica Zavoda za radiologiju i ultrazvuk Klinike i glavni radiološki tehnolog stupili su u kontakt s ovlaštenim servisom za održavanje uređaja. Servisni inženjeri proveli su kalibraciju detektora (s odgovarajućim fantomom) za točnost CT brojeva i uklanjanje prstenastih artefakata na snimkama., According to the Article 33 of the Act on Radiological and Nuclear Safety (Official Gazette 141/13; 39/15; 130/17; 118/18), Articles 14, 15 and 16 of the Ordinance on the conditions and measures of ionising radiation protection for performing activities involving ionising radiation sources (Official Gazette 53/18), radiological departments in Croatia that conduct diagnostic and interventional procedures in medicine using X-ray units should establish a Quality Assurance/Quality Control (QA/QC) programme for sources of ionizing radiation. Parameters that should be measured are defined in the Annexes 3-12 of the Ordinance on the conditions and measures of ionising radiation protection for performing activities involving ionising radiation sources (Official Gazette 53/18). Daily tests are performed by radiologic technologists, while more complex procedures are conducted by medical physicists, monthly or annually. While performing QC procedures, different scanning equipment is used to evaluate device parameters. In case of deviations from the recommended results, corrective measures for irregularity correction should be applied. All procedures must be registered and reported to the competent persons and institutions. The aim of this paper is to present a multidisciplinary approach in the QC program for the computed tomography (CT) scanner at the University Hospital for Infectious Diseases (UHID) in Zagreb, from March to September 2018. A multidisciplinary team consisted of radiologic technologists and a radiologist from UHID, radiologic technology students from the University of Applied Health Sciences in Zagreb and medical physicists from the Clinical Hospital Center Rijeka. Physicists advise radiologic technologists on the technical improvements in order to achieve the most efficient performance in their everyday QC procedures. All tested parameters were acceptable except for the detection of ring artefacts. To eliminate ring artefacts the head of the Department of Radiology and Ultrasound of the UHID and the principal radiologic technologist contacted the company certified for CT technical service and maintenance. Service engineer performed detector calibration procedure (with CT calibration phantoms) for CT number adjustment and image ring artefacts correction.

Introduction: The calculation algorithm for intensity modulated radiotherapy (IMRT) built in the Elekta Monaco treatment planning system (TPS) is based on Monte Carlo (MC) simulation. Absorbed dose is calculated as dose to medium in medium (Dm, m), but the conversion from Dm, m to dose to water in medium (Dw, m) is enabled. According to published data, differences between these two options exist, particularly in bony structures. In this study, comparisons between dose calculation options built in Elekta Monaco TPS and Monte Carlo N- Particle transport code® (MCNP) in different materials are shown. Furthermore, the majority of clinical experience is based on the dose to water in water (Dw, w) concept provided by analytical algorithms and has represented the standard for dose calculation over the past few decades. Additionally, MCNP calculation was performed to simulate the Dw, w concept. Therefore, the correlation between Dw, w concept, and both calculation options provided by the Elekta Monaco TPS was determined. Materials and methods: To evaluate the accuracy of TPS calculation options for 6MV photon beam, MCNP simulation was performed for 13 different materials with mass densities ranging from 0.2 g/cm3 to 2.17 g/cm3 using simplified geometry. The simulation was performed in two ways: with standard material representation taking into account their chemical compositions and corresponding mass densities and using non- standard material representation employing chemical composition of water with varying mass densities. Depth dose curves (DDs) calculated by MCNP were compared to those obtained by two calculation options Dm, m and Dw, m using Root Mean Square (RMS) deviations. Results: RMS deviations between depth dose curves (DDs), for Dm, m and Dw, m become largest for mass density 2.17 g/cm3, up to RMS=13%. Comparison for both calculation options to the MCNP defined for Dm, m shows very good agreement, with RMS deviation less than 3% for the majority of examined materials. For the Dw, m calculation option results are acceptable in mass density range from 0.5 g/cm3 (RMS=1.4%) to 1.06 g/cm3 (RMS=2.4%). For the rest of examined materials, RMS deviation increases, with a maximal value of 12.4%. Absorbed dose calculation comparison between Dw, m and non- standard MCNP shows large deviations for the majority of used materials, up to RMS=13.1%. RMS deviations between Dm, m calculation option and non-standard MCNP are much lower than one might expect. For the highest mass density in this research (2.17 g/cm3), the RMS deviation is 3.7%. Conclusion: Although it does not take into account the chemical composition of the medium, TPS calculation option Dm, m shows very good agreement with standard MCNP calculations. Furthermore, in our research, it is demonstrated that the Dw, m calculation option differs substantially from Dw, w. Additionally, it was found that for different materials absorbed dose calculated as Dm, m shows better agreement to the algorithms that calculate absorbed dose using Dw, w approach. Although the research was performed on simplified geometry, the results indicate that the use of Dm, m could be preferable in order to allow better consistency with previous clinical data in radiation oncology.

Majority of health institutions in Croatia do not have medical physicists in diagnostic radiology. Regarding this, in the west region of Croatia collaboration between public health institution and University Hospital Rijeka was initiated in 2015. Quality Assurance program was implemented in these public health institutions during 2015 and 2016 and the next step was to assess patient doses for the most frequent X-ray examinations. This included five public health institutions: 1 university hospital, 1 general hospital, 1 special hospital, 2 public health institutions with 13 facilities. The aim of this study was to carry out assessment of patient doses and to establish local diagnostic reference levels of entrance surface air kerma for every institution for six most frequent X-ray examinations. Also, local diagnostic reference levels for the whole west region of Croatia were established and compared with the national diagnostic reference levels and latest published data. Median entrance surface air kerma values for thorax PA, thorax LAT, cervical spine AP, thoracic spine AP, lumbar spine AP, pelvis AP and sinuses are 0.14 mGy, 0.50 mGy, 0.52 mGy, 1.50 mGy, 2.52 mGy, 2.03 mGy, and 1.03 mGy, respectively. Diagnostic reference levels proposed for our region were comparable with other studies.

Purpose: The goal of this work is to provide a large and consistent set of data for detector- specific output correction factors, k fclin ; fref Qclin ; Qref , for small static fields for seven solid-state detectors and to determine field output factors, Xfclin ; fref Qclin ; Qref , using EBT3 radiochromic films and W1 plastic scintillator as reference detectors on two different linear accelerators and four megavoltage photon beams. Consistent measurement conditions and recommendations given in the International Code of Practice TRS-483 for small- field dosimetry were followed throughout the study. Methods: Xfclin ; fref Qclin ; Qref were determined on two linacs, Elekta Versa HD and Varian TrueBeam, for 6 and 10 MV beams with and without flattening filter and for nine fields ranging from 0.5 9 0.5 cm2 to 10 9 10 cm2. Signal readings obtained with EBT3 radiochromic films and W1 plastic scintillator were fitted by an analytical function. Volume averaging correction factors, determined from twodimensional (2D) dose matrices obtained with EBT3 films and fitted to bivariate Gaussian function, were used to correct measured signals. k fclin ; fref Qclin ; Qref were determined empirically for six diodes, IBA SFD, IBA Razor, PTW 60008 P, PTW 60012 E, PTW 60018 SRS, and SN EDGE, and a PTW 60019 microDiamond detector. Results: Field output factors and detector- specific k fclin ; fref Qclin ; Qref are presented in the form of analytical functions as well as in the form of discrete values. It is found that in general, for a given linac, smallfield output factors need to be determined for every combination of beam energy and filtration (WFF or FFF) and field size as the differences between them can be statistically significant (P < 0.05). For different beam energies, the present data for k fclin ; fref Qclin ; Qref are found to differ significantly (P < 0.05) from the corresponding data published in TRS-483 mostly for the smallest fields (

The computed tomography has become a standard tool in radiation therapy treatment planning. Additionally, there is a growing awareness of the dose delivered to the part of the body outside the target volume. The ionizing radiation carries a stochastic risk of malignancy, therefore, the doses should be kept as low as reasonably achievable in order to provide an adequate information needed for the radiotherapy planning. The objective of this work was to set up the initial diagnostic reference levels and correlate to the image quality that would be used in the future optimization of localization scans. To quantify the doses from computed tomography localization scans at the University Hospital Rijeka, local diagnostic reference levels were established for five most common procedures of different anatomical regions; head, head and neck, pelvis, breast and thorax. The Computed Tomography Dose Index volumetric and the Dose-Length Product were used as dose indicators and scanning parameters were also recorded. The image quality assessment was performed for each set of images. The results were compared to the seldom published data in order to compare the clinical practice. The image quality for almost all of the body regions are scored as acceptable in average but require improvement. It is shown that the optimization of radiotherapy protocols is required. Therefore, these results will be used as a guideline for that process. The establishment of the national diagnostic reference levels for computed tomography localization procedures in radiation therapy is the next step and is currently an ongoing process.

Purpose: To assess the frequency, appropriateness, and radiation doses associated with multiphase computed tomography (CT) protocols for routine chest and abdomen–pelvis examinations in 18 countries. Materials and Methods: In collaboration with the International Atomic Energy Agency, multi-institutional data on clinical indications, number of scan phases, scan parameters, and radiation dose descriptors (CT dose–index volume; dose–length product [DLP]) were collected for routine chest (n = 1706 patients) and abdomen–pelvis (n = 426 patients) CT from 18 institutions in Asia, Africa, and Europe. Two radiologists scored the need for each phase based on clinical indications (1 = not indicated, 2 = probably indicated, 3 = indicated). We surveyed 11 institutions for their practice regarding single-phase and multiphase CT examinations. Data were analyzed with the Student t test. Results: Most institutions use multiphase protocols for routine chest (10/18 institutions) and routine abdomen–pelvis (10/11 institutions that supplied data for abdomen–pelvis) CT examinations. Most institutions (10/11) do not modify scan parameters between different scan phases. Respective total DLP for 1-, 2-, and 3-phase routine chest CT was 272, 518, and 820 mGy·cm, respectively. Corresponding values for 1- to 5-phase routine abdomen–pelvis CT were 400, 726, 1218, 1214, and 1458 mGy cm, respectively. For multiphase CT protocols, there were no differences in scan parameters and radiation doses between different phases for either chest or abdomen–pelvis CT ( P = 0.40-0.99). Multiphase CT examinations were unnecessary in 100% of routine chest CT and in 63% of routine abdomen–pelvis CT examinations. Conclusions: Multiphase scan protocols for the routine chest and abdomen–pelvis CT examinations are unnecessary, and their use increases radiation dose.

Purpose The goal of the present work was to provide a large set of detector-specific output correction factors for seven small volume ionization chambers on two linear accelerators in four megavoltage photon beams utilizing perpendicular and parallel orientation of ionization chambers in the beam for nominal field sizes ranging from 0.5 cm2 × 0.5 cm2 to 10 cm2 × 10 cm2 . The present study is the second part of an extensive research conducted by our group. Methods Output correction factors k Q clin , Q ref f clin , f ref were experimentally determined on two linacs, Elekta Versa HD and Varian TrueBeam for 6 and 10 MV beams with and without flattening filter for nine square fields ranging from 0.5 cm2 × 0.5 cm2 to 10 cm2 × 10 cm2 , for seven mini and micro ionization chambers, IBA CC04, IBA Razor, PTW 31016 3D PinPoint, PTW 31021 3D Semiflex, PTW 31022 3D PinPoint, PTW 31023 PinPoint, and SI Exradin A16. An Exradin W1 plastic scintillator and EBT3 radiochromic films were used as the reference detectors. Results For all ionization chambers, values of output correction factors k Q clin , Q ref f clin , f ref were lower for parallel orientation compared to those obtained in the perpendicular orientation. Five ionization chambers from our study set, IBA Razor, PTW 31016 3D PinPoint, PTW 31022 3D PinPoint, PTW 31023 PinPoint, and SI Exradin A16, fulfill the requirement recommended in the TRS-483 Code of Practice, that is, 0.95 k Q clin , Q ref f clin , f ref 1.05 , down to the field size 0.8 cm2 × 0.8 cm2 , when they are positioned in parallel orientation; two of the ionization chambers, IBA Razor and PTW 31023 PinPoint, satisfy this condition down to the field size of 0.5 cm2 × 0.5 cm2 . Conclusions The present paper provides experimental results of detector-specific output correction factors for seven small volume ionization chambers. Output correction factors were determined in 6 and 10 MV photon beams with and without flattening filter down to the square field size of 0.5 cm2 × 0.5 cm2 for two orientations of ionization chambers - perpendicular and parallel. Our main finding is that output correction factors are smaller if they are determined in a parallel orientation compared to those obtained in a perpendicular orientation for all ionization chambers regardless of the photon beam energy, filtration, or linear accelerator being used. Based on our findings, we recommend using ionization chambers in parallel orientation, to minimize corrections in the experimental determination of field output factors. Latter holds even for field sizes below 1.0 cm2 × 1.0 cm2 , whenever necessary corrections remain within 5%, which was the case for several ionization chambers from our set. TRS-483 recommended perpendicular orientation of ionization chambers for the determination of field output factors. The present study presents results for both perpendicular and parallel orientation of ionization chambers. When validated by other researchers, the present results for parallel orientation can be considered as a complementary dataset to those given in TRS-483.

NKG2D is an activating receptor that is expressed on most cytotoxic cells of the immune system, including NK cells, γδ and CD8+ T cells. It is still a matter of debate whether and how NKG2D mediates priming of CD8+ T cells in vivo, due to a lack of studies where NKG2D is eliminated exclusively in these cells. Here we studied the impact of NKG2D on effector CD8+ T-cell formation. NKG2D-deficiency that is restricted to murine CD8+ T cells did not impair antigen-specific T-cell expansion following mCMV and LCMV infection, but reduced their capacity to produce cytokines. Upon infection, conventional dendritic cells induce NKG2D ligands, which drive cytokine production on CD8+ T cells via the Dap10 signaling pathway. T-cell development, homing and proliferation were not affected by NKG2D deficiency and cytotoxicity was only impaired when strong T-cell receptor stimuli were used. Transfer of antigen-specific CD8+ T cells demonstrated that NKG2D-deficiency attenuated their capacity to reduce viral loads. The inability of NKG2D-deficient cells to produce cytokines could be overcome with injection of IL-15 super-agonist during priming. In summary, our data shows that NKG2D has a non-redundant role in priming of CD8+ T cells to produce antiviral cytokines. Upon viral infection, classical Dendritic cells induce expression of the NKG2D ligand H60. NKG2D stimulation during priming enhances the ability of CD8 T cells to produce cytokines but not increases cytotoxic potential upon T cell receptor engagement in the periphery.

The evaluation of the performance of nine physiotherapy ultrasound transducers used clinically was performed in the hospital environment using an acoustically absorbing thermocromic tile developed at the National Physical Laboratory (UK). The method consists of exposing an acoustic absorber tile, part of which contains a thermochromic pigment, to the ultrasonic beam, thereby forming an image of the intensity profile of the transducer. Images acquired using thermochromic materials were postprocessed in order to estimate effective radiating area (ERA) and beam nonuniformity ratio (BNR) for ultrasound transducers operating within the frequency range from 1.0 to 3.3 MHz, and nominal applied intensities in the range of 1 – 2 W / cm 2 . Results of our measurements have shown that thermocromic tile can be used for quality control of ultrasound transducers in the hospital environment. Experimental results show that proposed method can be used to distinguish highly non - uniform ultrasound beams with high value of BNR. Influence of exposure duration on obtained ERA and BNR values was also analysed. Our results show that values for ERA increase with insonation time, while BNR values decrease. In order to compare our results with theory we have estimated temperature rise in thermochromic material experimentally and compare it with theoretical prediction.

Interventional cardiac procedures may be associated with high patient doses and therefore require special attention to protect the patients from radiation injuries such as skin erythema, cardiovascular tissue reactions or radiation-induced cancer. In this study, patient exposure data is collected from 13 countries (37 clinics and nearly 50 interventional rooms) and for 10 different procedures. Dose data was collected from a total of 14,922 interventional cardiology procedures. Based on these data European diagnostic reference levels (DRL) for air kerma-area product are suggested for coronary angiography (CA, DRL = 35 Gy cm2), percutaneous coronary intervention (PCI, 85 Gy cm2), transcatheter aortic valve implantation (TAVI, 130 Gy cm2), electrophysiological procedures (12 Gy cm2) and pacemaker implantations. Pacemaker implantations were further divided into single-chamber (2.5 Gy cm2) and dual chamber (3.5 Gy cm2) procedures and implantations of cardiac resynchronization therapy pacemaker (18 Gy cm2). Results show that relatively new techniques such as TAVI and treatment of chronic total occlusion (CTO) often produce relatively high doses, and thus emphasises the need for use of an optimization tool such as DRL to assist in reducing patient exposure. The generic DRL presented here facilitate comparison of patient exposure in interventional cardiology. © 2018 Associazione Italiana di Fisica Medica

Background The accuracy of dose calculation is crucial for success of the radiotherapy treatment. One of the methods that represent the current standard for patient-specific dosimetry is the evaluation of dose distributions measured with an ionization chamber array inside a homogeneous phantom using gamma method. Nevertheless, this method does not replicate the realistic conditions present when a patient is undergoing therapy. Therefore, to more accurately evaluate the treatment planning system (TPS) capabilities, gamma passing rates were examined for beams of different complexity passing through inhomogeneous phantoms. Materials and methods The research was performed using Siemens Oncor Expression linear accelerator, Siemens Somatom Open CT simulator and Elekta Monaco TPS. A 2D detector array was used to evaluate dose distribution accuracy in homogeneous, semi-anthropomorphic and anthropomorphic phantoms. Validation was based on gamma analysis with 3%/3mm and 2%/2mm criteria, respectively. Results Passing rates of the complex dose distributions degrade depending on the thickness of non-water equivalent material. They also depend on dose reporting mode used. It is observed that the passing rate decreases with plan complexity. Comparison of the data for all set-ups of semi-anthropomorphic and anthropomorphic phantoms shows that passing rates are higher in the anthropomorphic phantom. Conclusions Presented results raise a question of possible limits of dose distribution verification in assessment of plan delivery quality. Consequently, good results obtained using standard patient specific dosimetry methodology do not guarantee the accuracy of delivered dose distribution in real clinical cases.

Advanced dose calculation algorithms for radiation therapy treatment planning can report external beam photon dose 2-sided, in terms of dose-to-medium (Dm) and dose-to-water (Dw). The purpose of our study was to determinate the effect of Dw and Dm reporting modes built in Elekta Monaco treatment planning system on intensity-modulated radiotherapy dose distributions for patients with nasopharyngeal cancer. For 13 patients involved in this retrospective study, 2 plans were created: 1 using Dw and another according to Dm reporting mode. Treatment plans were normalized such that 100% planning target volume should be covered by 95% of prescribed dose. Dose-volume constraints were assigned according to international standards. The comparison between dose distributions was performed evaluating quantities important for respective volumes of interest. For target volumes, heterogeneity index and conformity index methodology were used along with the maximum dose concept. Also, for the comparisons over particular organ at risk, maximum dose or mean dose as well as dose-volume concepts were used. For all target volumes and majority of organs at risk, the differences between 2 reporting modes are statistically insignificant, but this is not the case for bony structured organs at risks: mandible and cochlea. It was observed that Dw is higher than Dm with mean difference of 9.91% (p = 0.000009) of the mandible volume covered with 70 Gy. The same trend was observed for left and right cochlea with difference in mean dose of 8.74% (p = 0.037) and 6.87% (p = 0.029), respectively. The comparative analysis of dosimetric parameters in this study shows that the selection of reporting modes in Monaco treatment planning system can produce dose differences up to 15% in high-density volumes such as mandible and cochlea, which might have clinical consequences.

Natural killer group 2 member D (NKG2D) is an activating receptor that is expressed on most cytotoxic cells of the immune system, including NK cells, γδ, and CD8

Survey of Equipment Quality Control in Radiotherapy Centres in Croatia: First ResultsImplementation of advanced radiation therapy techniques in clinical practice can greatly improve tumour control and normal tissue sparing. An important part of this implementation is quality control (QC) of every part of the radiotherapy process, as it helps to detect errors and provides instant remedy. This increases the probability of successful radiation treatment and ensures patient radiation safety. Every radiotherapy quality assurance (QA) programme is based on quality control of radiotherapy equipment. The aim of our survey was to review QC practices in a number of radiotherapy centres in Croatia. As a first step, we defined a set of tests to check different parameters of linear accelerators and simulators in these centres. The tests were defined and performed according to protocols developed at two university hospitals. Test results varied largely between the centres. This calls for harmonisation of QC protocols.

Intracavitary application of brachytherapy sources followed by external beam radiation is essential for the local treatment of carcinoma of the cervix. Due to very high doses to the central portion of the target volume delivered by brachytherapy sources, this part of the target volume must be shielded while being irradiated by photon beams. Several shielding techniques are available, from rectangular block and standard cervix wedge to more precise, customized step wedge filters. Because the calculation of a step wedge filter's shape was usually based on effective attenuation coefficient, an approach that accounts, in a more precise way, for the scattered radiation, is suggested. The method was verified under simulated clinical conditions using film dosimetry. Measured data for various compensators were compared to the numerically determined sum of the dose distribution around brachytherapy sources and one of compensated beam. Improvements in total dose distribution are demonstrated, using our method. Agreement between calculation and measurements were within 3%. Sensitivity of the method on sources displacement during treatment has also been investigated.

Introduction The clinical effects of ultrasound used for physiotherapy depend on applied intensity and time of insonation. Output intensities of 0.1–3.0 W/cm 2 are typically applied for therapeutic purposes in pulsed or continuous modes. In order to accurately measure the output characteristics of ultrasonic therapy transducers, an evaluation of effective radiating area (ERA) and beam homogeneity must be made regularly in order to prevent patient damage. Purpose Implementation of the method based on use of thermochromic tile in clinical environment for the verification of ultrasound fields produced by transducers used for physiotherapy. Materials and methods In this work non-standardized method developed at National Physical Laboratory (NPL) was used for quality assurance of ultrasound therapy beams. The method consists of exposing thermocromic tile to the ultrasonic beam thereby forming an thermal image of the intensity profile of transducer. The image is in turn photographed and analyzed using software developed for that purpose. Results Several physiotherapy ultrasound transducers clinically used were tested by use of thermocromic tile in the hospital environment. Thermal images were postprocesed in order to estimate effective radiating area and beam nonuniformity ratio (BNR) for tested transducers. Conclusion Results of our measurements have shown that thermocromic tile can be used for rapid check of ultrasound transducers in the hospital environment. Furthermore, our work has also shown that it is possible postprocess thermal images in order to calculate some beam parameters such as effective radiating area (ERA) and beam nonuniformity ratio (BNR).

At present, high energy electron linear accelerators (LINACs) producing photons with energies higher than 10 MeV have a wide use in radiotherapy (RT). However, in these beams fast neutrons could be generated, which results in undesired contamination of the therapeutic beams. These neutrons affect the shielding requirements in RT rooms and also increase the out-of-field radiation dose to patients. The neutron flux becomes even more important when high numbers of monitor units are used, as in the intensity modulated radiotherapy. Herein, to evaluate the exposure of patients and medical personnel, it is important to determine the full radiation field correctly. A model of the dual photon beam medical LINAC, Siemens ONCOR, used at the University Hospital Centre of Osijek was built using the MCNP611 code. We tuned the model according to measured photon percentage depth dose curves and profiles. Only 18 MV photon beams were modeled. The dependence of neutron dose equivalent and energy spectrum on field size and off-axis distance in the patient plane was analyzed. The neutron source strength (Q) defined as a number of neutrons coming from the head of the treatment unit per x-ray dose (Gy) delivered at the isocenter was calculated and found to be 1.12 × 10 12 neutrons per photon Gy at isocenter. The simulation showed that the neutron flux increases with increasing field size but field size has almost no effect on the shape of neutron dose profiles. The calculated neutron dose equivalent of different field sizes was between 1 and 3 mSv per photon Gy at isocenter. The mean energy changed from 0.21 MeV to 0.63 MeV with collimator opening from 0 × 0 cm 2 to 40 × 40 cm 2 . At the 50 cm off-axis the change was less pronounced. According to the results, it is reasonable to conclude that the neutron dose equivalent to the patient is proportional to the photon beam-on time as suggested before. Since the beam-on time is much higher when advanced radiotherapy techniques are used to fulfill high conformity demands, this makes the neutron flux determination even more important. We also showed that the neutron energy in the patient plane significantly changes with field size. This can introduce significant uncertainty in dosimetry of neutrons due to strong dependence of the neutron detector response on the neutron energy in the interval 0.1–5 MeV.

Introduction Implementation of advanced radiotherapy techniques makes high demands on the treatment planning system (TPS). Purpose Dosimetric evaluation of calculation algorithm built in Monte Carlo (MC) based TPS. Materials and methods Dose distributions of different complexity were calculated using Elekta Monaco TPS. Both calculation methods (Dose to Water-D2W and Dose to Medium-D2M) for 6MV photon beam were verified using 2D detector and ionization chambers of different volumes in inhomogenous phantom. Results Comparison of measured and calculated data in point of ‘tissue’ and low density medium show good agreement regardless the calculation method. In high density medium deviation was much higher. Also, deviations of measured and values calculated as D2W and D2M, respectively, were larger and of opposite signs. To overcome this we propose to define minimum volume of water cylinder to be placed within high density medium. This volume should allow that D2W and D2M calculated doses differ less than 0.5% and consequently good agreement with measurements. Furthermore, 2D methodology used for patient specific dosimetry was used to evaluate TPS accuracy, but antrophomorphic thorax phantom was used instead of the homogeneous one. Anlayze shows that gamma criterion 3% or 3mm was not fulfilled when inhogeneities are inside treated volume. Conclusion MC TPS evaluation using point dose measurements show large uncertainties within high density medium. It can be overcome by using proposed approach. Also, despite the manufacturer’s claim of 2D verification superiority over point measurements, our investigation shows otherwise when measurements in inhomogeneous phantom are considered.

The use of compensators in order to achieve desired dose distribution has a long history and is a well-established technique in radiation therapy planning. There are several different calculation methods for determining a compensator's thickness. An alternative method that is based on the Cunningham's modification of Clarkson's method to calculate scattered radiation in beams with an inhomogeneous cross-section is proposed. It is well known that the total dose distribution of radiotherapy photon beam consists of the contributions of the primary beam, attenuated by the tissue layer, and the scattered radiation generated by the primary radiation in single and multiple photon scatter events. The scattered component can be represented as a function of the primary radiation. The central point of our method is the numerical estimation of the primary distribution required to achieve the desired total distribution. Now using the calculated primary distribution, the shape of the modulator could be determined. In this way the contribution of the scattered component is validated in a more accurate way than using effective attenuation coefficients, which is a common practice. The method is verified in various clinical situations and compared with the standard method. The accuracy, although dependent on geometry, was improved by at least 2%. With more complex geometries there is an even higher gain in accuracy with our method when compared to the standard method.

The implementation of the non-standardized method developed at the National Physical Laboratory (UK) supporting the quality assurance of therapeutic ultrasonic beam parameters within a clinical environment is presented. The method consists of exposing an acoustic absorber tile, part of which contains a thermochromic pigment, to the ultrasonic beam, thereby forming an image of the two-dimensional intensity profile of the transducer. Nine different physiotherapy ultrasound treatment heads currently used clinically were tested using this method. Thermochromic images were postprocessed in order to estimate the Effective Radiating Area (ERA) for treatment heads operating within the frequency range from 1 MHz to 3.2 MHz, and nominal applied intensities in the range of 1 W/cm2 to –3 W/cm2. Experimental results and comparisons with manufacturer specified values of ERA are presented. Differences in the experimentally derived results and the manufacturer values are typically well within 25%. The root-mean squared difference calculated over the nine treatment heads is 15.1%, with the thermochromic material tended to underestimate the ERA.

Propagation of ultrasound through biological structures produces thermal and nonthermal (mechanical) effects. Those effects can be used in medical application of low intensity ultrasound for physiotherapy [1]. The therapeutic ultrasound administration implies into a variety of energy and time dosage to achieve clinical results, which are associated to the increase of tissue temperature to healing rates. Tissue temperature increases due the intensity levels irradiated through the patient’s body. However, high intensity levels can generate excessive heat what can be dangerous to biological tissue. Thus quality control of physiotherapy ultrasound equipment performance plays a very important role. Acceptability of ultrasound beam for clinical use can be verified measuring uniformity of its acoustic intensity. Beam homogeneity can be quantified by the parameter called beam non- uniformity ratio (BNR), which represent the ratio of the highest intensity in the field to the average intensity. Value of the area over which ultrasonic power is emitted denotes the parameter effective radiating area (ERA). These parameters of ultrasound transducer could change during time and as such should be part of quality assurance program and checked on regular basis. The standardised method for beam uniformity verification is based on the scanning of the acoustic field in water tanks using miniature hydrophones. Unfortunately this method is not very convenient for use in hospital environment. An alternative method based on the use of thermochromic materials was proposed by Butterworth et al. [2]. Method consists in placing an acoustic absorber tile containing a thermochromic pigment in cross- section of the ultrasonic beam, forming an image of the temperature distribution. This method gives information about whole thermal pattern, which is related to the intensity of ultrasound, offering a qualitative measurement. While the thermochromic materials can provide rapid qualitative data to the naked eye, the quality of this data can be improved through image capture and post processing. In this paper the evaluation of this method in clinical conditions was presented. Seven physiotherapy ultrasound transducers clinically used in University Hospital Rijeka were tested by using thermochromic material. A systematic image capture protocol has been applied. Images are taken before and after ultrasonic exposure. All thermochromic images were postprocessed in order to calculate beam parameters ERA and BNR. The ERA and BNR were determined for transducers with frequency in range from 1 MHz to 3.3 MHz, and intensity range of 1W/cm2 to 3W/cm2. Experimental results and the comparisons with specified transducers performance will be presented.

Introduction Increased neutron flux around high energy medical electron linear accelerators placed in the rooms reconstructed after decommissioning of 60Co unit has been reported before. Purpose The main limitation of the reported room was the space. Extremely short maze was used and walls were strengthened by lead. In this study, Monte Carlo simulation is used to analyze the reasons for increased neutron flux. Materials and methods A model of 18 MV photon beam linear accelerator with the room was built using the MCNP611 code. Points at several locations and different accelerator orientations were used to evaluate the neutron and photon ambient dose equivalent to which medical personnel could be exposed. Also, the different maze lengths was used in simulation to evaluate its significance for neutron protection. Then neutron sources, spectra, flux and dose equivalent were analyzed. Results Calculated neutron dose equivalent was not negligible from the aspect of personal dosimetry with almost 2 mSv/year per person in area occupied by staff (conservative estimation). The wall enhancement by lead was new source of photoneutrons. Simulated longer mazes significantly decreased neutron flux near the room door. Both, the lead enhancements and different lengths of mazes changed neutron spectra significantly in chosen points. Conclusion The study confirms that shielding from neutron radiation should be thoroughly analyzed if high energy linear accelerators are put in the room where the space constraints exist. The lead enhancement of walls and short mazes should be avoided. If this is not possible, lower energy photon beams should be used.

Implementation of advanced techniques in clinical practice can greatly improve the outcome of radiation therapy, but it also makes the process much more complex with a lot of room for errors. An important part of the quality assurance program is verification of treatment planning system (TPS). Dosimetric verifications in anthropomorphic phantom were performed in 4 centers where new systems were installed. A total of 14 tests for 2 photon energies and multigrid superposition algorithms were conducted using the CMS XiO TPS. Evaluation criteria as specified in the International Atomic Energy Agency Technical Reports Series (IAEA TRS) 430 were employed. Results of measurements are grouped according to the placement of the measuring point and the beam energy. The majority of differences between calculated and measured doses in the water-equivalent part of the phantom were in tolerance. Significantly more out-of-tolerance values were observed in “nonwater-equivalent” parts of the phantom, especially for higher-energy photon beams. This survey was done as a part of continuous effort to build up awareness of quality assurance/quality control (QA/QC) importance in the Croatian radiotherapy community. Understanding the limitations of different parts of the various systems used in radiation therapy can systematically improve quality as well.

Introduction. External photon beam modulation using compensators in order to achieve a desired dose distribution when brachytherapy treatment is followed by external beam radiation is a well-established technique. A compensator modulates the central part of the beam, and the dose beneath the thickest part of the compensator is delivered mostly by scattered, low energy photons. A two-dimensional detector with a good spatial resolution is needed for the verification of those beams. In this work, the influence of different types of detectors on the measured modulated dose distributions was examined. Materials and methods. Dosimetric verification was performed using X-Omat V, Eastman Kodak radiographic films at different depths in a solid water phantom. The film measurements were compared with those made by ionization chambers. Photon beams were also modelled using EGSnrc Monte Carlo algorithm to explain the measured results. Results. Monte Carlo calculated over-response of the film under the thickest part of the compensator was over 15%, which was confirmed by measurements. The magnitude of over-response could be associated with changes in the spectra of photon energy in the beam. Conclusions. The radiographic film can be used for the dosimetry of compensated high energy photon beams, with limitations in volumes where photon spectra are hardly degraded.

Radioterapija megavoltnim snopovima fotona linearnog akceleratora oblik je lokalnog onkološkog liječenja. Njezin je cilj predati propisanu apsorbiranu dozu ciljnom volumenu, uz što nižu dozu okolnomu zdravom tkivu. Proces se sastoji od niza koraka u kojima sudjeluje tim stručnjaka iz različitih područja. Veliki broj postupaka i ljudi uključenih u radioterapijski proces, nepouzdanosti uređaja te pomaci bolesnika i unutrašnjih organa tijekom terapije mogu uzrokovati odstupanja između planirane i stvarne raspodjele doze. U ovom radu procijenili smo utjecaj pogreške položaja bolesnika tijekom terapije na raspodjelu doze, te na veličine koje služe za procjenu kvalitete plana. Pogreške u položaju bolesnika ispitane su u skupini od 35 bolesnika. Te smo pogreške simulirali na pet bolesnika, koristeći se 3D programom za planiranje XiO (CMS Inc., St. Louis, MO, Elekta). Ispitali smo razlike u raspodjeli doze između planiranog i stvarnog položaja. Dodatno, utjecaj pogrešaka na odabir plana zračenja provjerili smo analizirajući promjene u dozno-volumnom histogramu (DVH), pokrivenost planiranog volumena (engl. PTV conformity index, CIPTV) i jednoličnost raspodjele doze u ciljnom volumenu (engl. homogeneity index, HI). Simulacije pokazuju da promjene u položaju bolesnika mogu uzrokovati značajne razlike između planirane i stvarne raspodjele doze. Kod nekih bolesnika ako se ne korigiraju pogreške, CIPTV postaje manji od 97 % što znači da plan više nije prihvatljiv za zračenje. Iznenađuje da HI nije ovisan o pomacima bolesnika kao CIPTV. Rezultati pokazuju potrebu za smanjenjem pogrešaka, što se može postići provođenjem kontrole kvalitete u radioterapiji., An external beam radiotherapy (EBRT) using megavoltage beam of linear accelerator is usually the treatment of choice in cancer patients. The goal of EBRT is to deliver the prescribed dose to the target volume, with as low as possible dose to the surrounding healthy tissue. A large number of procedures and different professions involved in radiotherapy, uncertainty of equipment and daily patient set-up errors can cause a difference between the planned and delivered dose. We investigated a part of this difference caused by measuring daily patient set-up errors for 35 patients. These set-up errors were simulated on five patients, using 3D treatment planning software XiO. The simulation investigated differences in dose distributions between the planned and shifted geometry. Additionally, we investigated the influence of the error on treatment plan selection by analysing changes in dose volume histograms, planning target volume conformity index (CIPTV), and homogeneity index (HI). Simulations showed that patient daily set-up errors can cause significant differences between the planned and actual dose distributions. Moreover, for some patients, those errors could affect the choice of treatment plan since CIPTV fell under 97 %. Surprisingly, HI was not as sensitive to set-up errors as CIPTV. Our results have confirmed the need to minimise daily set-up errors through quality assurance programmes.

In this paper polarization effects in the nuclear excitation by positron–electron annihilation (NEPEA) process are considered. We calculated cross-sections for the NEPEA with wave functions of bound electron and incoming positron in point nuclear Coulomb field. The results are compared to predictions which are derived using Born approximation. Results for the annihilation on the K-electron are presented. We found that cross-section for magnetic transition is much more pronounced for orientation of electron spin in positron direction. For electric transition cross-sections with parallel spin orientation are larger than for antiparallel, at least for small positron energy.

Patients with cervical, uterine, and rectal carcinomas are usually treated in the prone position using the bellyboard positioning device. Specific and uncomfortable prone position gives rise to uncertainties in the daily set-up of patients during the treatment. During investigation of translational movements, rotational movements of the pelvis are observed and investigated. The film portal imaging is used to discover patient positioning errors during treatment. We defined the rotational set-up errors by angle deviations of the sacrum. Thirty-six patients were included in the study; 15 patients were followed during the whole treatment and 21 during the first 5 consecutive treatment days. The image acquisitions were completed in 84%. Systematic and random positioning errors were analyzed in 725 images. Approximately half of the patients had adjusted to the bellyboard in the first few fractions, with sacrum angles remaining the same for the rest of the treatment. The other half had drifts of the sacrum angle during the whole treatment. The rotation of the sacrum during treatment ranged up to 14 degrees , causing the usual set-up verification and correction procedure to result in errors up to 15 mm. Rotational movements of the patient pelvis during bellyboard pelvis radiotherapy can introduce considerable patient position error.

During implementation of the total skin electron treatment, using six-dual-field technique, at radiotherapy department a large number of measurements are needed. To assess depth dose curve required by clinicians and dose uniformity over a whole treatment plane, combinations of different irradiation parameters are used (electron energy, beam angle, scatterers). Measurements for each combination must be performed. One possible way to reduce number of measurements is to model the treatment using the Monte Carlo simulation of electron transport. We made a simplified multiple-source Monte Carlo model of electron beam and tested it by comparing calculations and experimental results. Calculated data differs less than 5 percent from measurements in the treatment plane. During the treatment patient can be approximated using cylinders with different diameters and orientations. We tried to model the depth dose variations in the total skin electron treatment not just around the body cross-section (simplified to cylinders of different diameters), but also along the body to account for the variations in body curvature longitudinally. This effect comes down to the problem of modeling distribution in different cylinders, but varying the longitudinal orientation of those cylinders. We compared Monte Carlo calculations and film measurements of depth dose curves for two orientations of the cylindrical phantom, which were the simplest for experimental arrangement. Comparison of the results proved accuracy of the model and we used it to calculate depth dose curves for a number of other cylinder orientations.

During implementation of the total skin electron treatment, using six-dual-field technique, at radiotherapy department a large number of measurements are needed. To assess depth dose curve required by clinicians and dose uniformity over a whole treatment plane, combinations of different irradiation parameters are used (electron energy, beam angle, scatterers). Measurements for each combination must be performed. One possible way to reduce number of measurements is to model the treatment using the Monte Carlo simulation of electron transport. We made a simplified multiple-source Monte Carlo model of electron beam and tested it by comparing calculations and experimental results. Calculated data differs less than 5 percent from measurements in the treatment plane. During the treatment patient can be approximated using cylinders with different diameters and orientations. We tried to model the depth dose variations in the total skin electron treatment not just around the body cross-section (simplified to cylinders of different diameters), but also along the body to account for the variations in body curvature longitudinally. This effect comes down to the problem of modeling distribution in different cylinders, but varying the longitudinal orientation of those cylinders. We compared Monte Carlo calculations and film measurements of depth dose curves for two orientations of the cylindrical phantom, which were the simplest for experimental arrangement. Comparison of the results proved accuracy of the model and we used it to calculate depth dose curves for a number of other cylinder orientations.