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Breast cancer is the most frequently diagnosed tumor in pregnant women and radiation therapy should carefully be weighted up because of the dose to the fetus. The aim of this study was to investigate fetal dose in a patient treated with Virtual Tangential-fields Arc Therapy (ViTAT), an innovative technique for whole breast irradiation. Optically stimulated luminescence detectors (OSLDs) were calibrated on a Varian TrueBeam linac, with both a 6X and 6XFFF beam quality, and used for out-of-field measurements. Fetal dose related with ViTAT technique was compared to the standard 3D conformal radiation therapy technique (3DCRT). The fetal dose delivered with a ViTAT technique planned with 6XFFF beam was also investigated. Measurements were taken on a phantom composed of Rando Alderson Phantom slices and solid water slabs. OSLDs were placed in a region identified by the height of the fundus from conception to the twentieth week using a custom made PMMA grid. Due to the higher number of monitor units, the peripheral dose of ViTAT delivered with 6X beams is higher than that of 3DCRT. However, nanoDots measurements prove that ViTAT can be used in place of 3DCRT while maintaining similar fetal dose levels if 6XFFF beams are used.

Purpose The aim of this multicenter study was to evaluate the performance of the upgraded version of the Ingenuity TF PET/CT scanner, according to the NEMA NU-2 2012 standards. Methods Spatial resolution, sensitivity, count rate response, scatter fraction, image quality and accuracy were evaluated on three Ingenuity TF scanners installed in Italian hospitals. Furthermore, energy and timing resolution were measured. A detailed image quality phantom analysis was performed to evaluate the effect of different clinical reconstruction parameters, including the application of PSF correction. Results Results show an average spatial resolution of 4.7 mm and an average absolute system sensitivity of 7.9 cps/kBq. The average maximum NECR was 119.83 kcps at 20.67 kBq/ml, while the maximum true event rate was 322.62 kcps at the concentration of 24.51 kBq/ml. The average maximum bias below NECR peak was 12.58%. All the results of NEMA tests were in agreement with the values declared by the manufacturer. The estimated average energy and timing resolution were 10.83% and 536.2 ps, respectively. Image quality phantom analysis obtained with different reconstruction settings showed that PSF correction was the parameter that affected mainly on contrast recovery coefficient, while the iteration number and amplitude of Gaussian filter had no significant effect. Of relevance, the application of PSF correction never led to recovery coefficient values higher than 100% and to Gibbs or edge artifacts. Conclusions The new Ingenuity TF model shows physical performance similar to other scanners of the latest generation for all standard NEMA NU2-2012 measurements.

Purpose To define weight-stratified Diagnostic Reference Levels (DRL) typical values for pediatric interventional cardiology (IC) procedures adopting standardized methodologies proposed by ICRP135 and RP185. Methods Procedures performed at the pediatric catheterization room of the University-Hospital of Padua were analysed. Patients were stratified into body weight (BW) classes and DRL quantities were analysed for the most performed procedures. Typical values are defined as median PKA and Ka,r. For database consistency, sampling and exclusion methods were precisely defined. The DRL-curve methodology by means of quantile regression median curves was investigated to assess the relationship between PKA and weight. A like-to-like comparison with literature was made. Results 385 procedures were analysed. A large PKA variability was observed in each weight group. PKA differences across BW groups were not always statistically significant. When stratifying by procedure, PKA variability decreased while correlations of PKA and PKA/FT with weight increased. The established typical values are generally lower than DRLs published data, whatever stratification method adopted. The highest PKA median values were observed for Angioplasty (4.9 and 11.6 Gycm2 for 5- Conclusions Typical values for pediatric IC DRL quantities were determined according to ICRP135 and RP185 methodologies. Stratification by BW classification does not reduce the variability of the PKA values, unlike what happens when stratifying by procedure type. Results seem to corroborate that variability and exposure are more affected by procedure type and complexity than by patient weight. DRL-curve is a feasible approach.

Purpose This study measured to which extent RapidPlan can drive a reduction of the human-caused variability in prostate cancer treatment planning. Methods Seventy clinical prostate plans were used to train a RapidPlan model. Seven planners, with different levels of planning experience, were asked to plan a VMAT treatment for fifteen prostate cancer patients with and without RapidPlan assistance. The plans were compared on the basis of target coverage, conformance and OAR sparing. Inter-planner and intra-planner variability were assessed on the basis of the Plan Quality Metric formalism. Differences in mean values and InterQuartile Ranges between patients and operators were assessed. Results RapidPlan-assisted plans matched manual planning in terms of target coverage, homogeneity, conformance and bladder sparing but outperformed it for rectum and femoral heads sparing. 8 out of 15 patients showed a statistically significant increase in overall quality. Inter-planner variability is reduced in RapidPlan-assisted planning for rectum and femoral heads while bladder variability was constant. The inter-planner variability of the overall plan quality, IQR of PQM%, was approximately halved for all patients. RapidPlan assistance induced a larger increase in plan quality for less experienced planners. At the same time, a reduction in intra-planner variability is measured with a significant overall reduction. Conclusions The assistance of RapidPlan during the optimization of treatments for prostate cancer induces a significant increase of plan quality and a contextual reduction of plan variability. RapidPlan is proven to be a valuable tool to leverage the planning skills of less experienced planners ensuring a better homogeneity of treatment plan quality.

Purpose In the setting of thorax Computed Tomography (CT), the main purpose of this work is to quantify differences in Size-Specific Dose Estimate (SSDE), calculated on the basis of both effective diameter and water-equivalent diameter, accounting for patient size and tissue attenuation, respectively. Materials and methods An in-house software was developed to measure water-equivalent diameter and effective diameter on each CT slice, for 133 CT examinations. SSDE was calculated according to the Report of American Association of Physicists in Medicine Task Group (AAPM TG) 204 and 220. The ratio between effective and water-equivalent diameters was studied as function of cross-sectional air-to-body area ratio, for the slice located in the middle of the scan range. Results When AAPM TG 220 prescriptions were applied, SSDE was mostly found larger than that obtained with AAPM TG 204 recommendations. On average, a difference of about 12% was observed, in spite of a considerable variability (from −18% to 53%). The ratio between effective and water-equivalent diameters ranged from 0.97 to 1.31, with a mean value of 1.15. Moreover, it was found considerably correlated with cross-sectional air-to-body ratio (Pearson's coefficient was 0.78 for women, 0.90 for men). Conclusion The discrepancy obtained by calculating SSDE on the basis of AAPM TG 204, instead of AAPM TG 220 Report, may vary substantially. Fluctuations were justified by the variability observed in the relative amount of low attenuating tissues in body, which was proved to be considerably correlated to the ratio between effective and water-equivalent diameters.

[Purpose] To perform a systematic and thorough assessment, using the Uncomplicated and Cancer-Free Control Probability (UCFCP) function, of a broad range of photon prostate cancer RT treatments, on the same scenario (a unique pelvic CT set). UCFCP considers, together with the probabilities of local tumour control (TCP) and deterministic (late) sequelae (NTCP), the second primary cancer risk (SPCR) due to photon and neutron peripheral doses., [Methods and materials] Thirty-six radiotherapy plans were produced for the same CT. 6, 10, 15 and 18 MV 3DCRT, IMRT and VMAT (77.4 Gy in 43 fractions) and 6 and 10 MV SBRT (36.25 Gy in 5 fractions with flattened and FFF beams) for Elekta, Siemens and Varian Linacs plans were included. DVH and peripheral organ dosimetry were used to compute TCP, NTCP, and SPCR (the competition and LNT models) for further plan ranking., [Results] Biological models (and parameters) used predicted an outcome which is in agreement with epidemiological findings. SBRT plans showed the lowest SPCR and a below average NTCPrectal. High energy plans did not rank worse than the low energy ones. Intensity modulated plans were ranked above the 3D conformal techniques., [Conclusions] According to UCFCP, the best plans were the10 MV SBRTs. SPCR rates were low and did not show a substantial impact on plan ranking. High energy intensity-modulated plans did not increase in excess the average of SPCR. Even more, they ranked among the best, provided that MU were efficiently managed., BSN acknowledges the support of Conicyt FONDECYT Regular 2018 (N1181133) and of Pontificia Universidad Católica de Chile [EPB2016, P1702/2017 and “Concurso de Apoyo a Sabáticos Internacionales 2017”]. MRE would like to thank Banco Santander for its support through the grant program ‘‘Becas Iberoamérica. Jóvenes Profesores e Investigadores y Alumnos de Doctorado Santander Universidad”.

Purpose The evaluation of features robustness with respect to acquisition and post-processing parameter changes is fundamental for the reliability of radiomics studies. The aim of this study was to investigate the sensitivity of PET radiomic features to acquisition statistics reduction and standardized-uptake-volume (SUV) discretization in PET/MRI pediatric examinations. Methods Twenty-seven lesions were detected from the analysis of twenty-one 18F-FDG-PET/MRI pediatric examinations. By decreasing the count-statistics of the original list-mode data (3 MBq/kg), injected activity reduction was simulated. Two SUV discretization approaches were applied: 1) resampling lesion SUV range into fixed bins numbers (FBN); 2) rounding lesion SUV into fixed bin size (FBS). One hundred and six radiomic features were extracted. Intraclass Correlation Coefficient (ICC), Spearman correlation coefficient and coefficient-of-variation (COV) were calculated to assess feature reproducibility between low tracer activities and full tracer activity feature values. Results More than 70% of Shape and first order features, and around 70% and 40% of textural features, when using FBS and FBN methods respectively, resulted robust till 1.2 MBk/kg. Differences in median features reproducibility (ICC) between FBS and FBN datasets were statistically significant for every activity level independently from bin number/size, with higher values for FBS. Differences in median Spearman coefficient (i.e. patient ranking according to feature values) were not statistically significant, varying the intensity resolution (i.e. bin number/size) for either FBS and FBN methods. Conclusions For each simulated count-statistic level, robust PET radiomic features were determined for pediatric PET/MRI examinations. A larger number of robust features were detected when using FBS methods.

Objective To provide guidance for reliable identification of low-activity sentinel nodes in the setting of melanoma surgery using a commercial hand-held gamma camera. Methods The average uptake of 99mTc nanocolloid by sentinel nodes was evaluated in 95 excised nodes using a Sentinella 102® (Oncovision, Valencia, Spain) portable gamma camera. The device sensitivity was assessed for different source depths and collimator distances, imaging an 8-mm sphere filled with a known-activity solution of 99mTc. Five nuclear medicine physicians were asked to identify the source at different activity levels and positions within the field of view. For each image the number of signal counts inside a circular region of interest (ROI) was measured, while the variability of ROI counts among operators was assessed. The number of counts providing a minimal, near-constant inter-operator variability was determined as a criterion for a consistent identification of the source. Either the minimum activity or the acquisition time needed to collect the appropriate statistics were then calculated. Results The median SN uptake (0.5%) turned out to be compatible with values reported in the literature. The sensitivity of the compact gamma camera ranged from ∼25 cpm/kBq to ∼1 cpm/kBq. A total of 50 counts in the ROI circumscribing the lymph node-simulating sphere appeared to be a robust criterion for identification of the source. Conclusions Ten megabecquerels of injected activity at the time of surgery and one minute of acquisition allows reliable identification of sentinel nodes for collimator-to-source distances up to 10 cm.

Purpose the aim of this study was to evaluate the stability of image quality (IQ) metrics in pediatric 18F-FDG PET/MR acquisitions while decreasing statistical counts, mimicking an injected activity reduction. Methods 21 18F-FDG PET/MR whole body acquisitions performed on an hybrid scanner (Biograph mMR, Siemens Healthcare) were retrospectively reconstructed with the e7-tools package. The full tracer activity (FTA) list-mode data (3 MBq/kg, 5 min/bed position) were truncated at 4, 3, 2.5, 2 and 1 min, simulating lower tracer activity (LTA) images corresponding to 2.4, 1.8, 1.5, 1.2 and 0.6 MBq/kg. Subjective IQ (score 1 to 5) and number of detectable lesions were assessed by two expert nuclear medicine physicians. SUV metrics (SUVmean, SUVmax and SUVpeak) and semi-quantitative parameters as contrast-to-noise ratio (CNR), normalized noise in liver (NN), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were evaluated on each image. Results Results of subjective IQ evaluations are reported in Fig. 1; the assigned score decreased when reducing tracer activity, but remained acceptable till 1.5 MBq/kg. All the total 56 lesions were detected until 1.2 MBq/kg activity level, whereas 5 lesions were missed on the 0.6 MBq/kg image. Results of quantitative analysis are collected in Table 1 , espressed as a ratio of LTA and FTA values. Semi-quantitative parameters (except SUVpeak) and IQ metrics showed limited variation respect to the FTA image until 1.5 MBq/kg image. Differences were not statistically significant in LTA images down to 1.5 MBq/kg with pairwise paired Wilcoxon and t-tests. SUVpeak is the parameter less affected by dose reduction (average difference for all LTA images inferior than 2%). NN showed a constant increase while decreasing statistical counts. Conclusions An injected activity reduction up to 50% (1.5 MBq/kg) guarantees a stability in semi-quantitative parameters representing lesion detectability and tumor burden information.

Purpose The aim of this preliminary study was to assess the compatibility of dedicated positioning devices developed for MR/PET imaging integration into radiotherapy planning. Methods The X-Tend Flat Table Top and specifically designed radiofrequency coil holders were tested on an integrated Biograph mMR MR/PET scanner (Siemens Healthcare). Magnetic field homogeneity and MR image quality in terms of artifacts and signal-to-noise ratio (SNR), with and without the radiotherapy positioning devices, were evaluated by means of a field sequence with 0.1 ppm/line and a clinical T2-weighted sequence, respectively. Acquisitions of a cylindrical (diameter 16 cm) doped (NiSO4) water phantom were performed by using a flexible 8-channel radiofrequency coil. SNR was estimated through the subtraction method. Since glass fiber table top and radiofrequency coil holders can attenuate PET signal, introducing potential quantification errors, PET photon attenuation was tested by the use of a cylindrical uniform phantom filled with 18-F and a sealed 68-Ge phantom. Also, a CT scan of the equipment was performed to calculate the transmission factor at 511 keV. Results The use of the dedicated radiotherapy positioning devices did not affect appreciably magnetic field homogeneity, and did not yield evident artifacts in T2-weighted images. When using the radiotherapy devices, SNR showed a reduction of less than 5% with respect to standard MR acquisitions. The average transmission factor of the radiotherapy table was computed to be around 90% from both CT scan and PET photon attenuation. Conclusions Based on our preliminary results, the dedicated radiotherapy positioning devices seem to be MR and PET compatible. Effect of radiotherapy devices on MR geometrical distortion and image uniformity, also for non-conventional quantitative diffusion-weighted imaging (a useful and sensitive tool for oncologic applications), are under evaluation. Further investigation is needed to assess the effect of radiotherapy table attenuation on PET contrast of lesions.

Purpose An open issue of radiomic is its robustness in respect to image acquisition and post-processing parameters changes. The aim of this study is to evaluate the stability of PET radiomic features when decreasing injected activity in pediatric PET/MRI for their potential use for lesion biologic characterization in low-activity examinations. Moreover, different SUV resampling and contouring strategies were investigated. Methods Fifty-six lesions detected in 21 whole-body 18F-FDG-PET/MRI pediatric examinations (3 MBq/kg, 5 min/bed) performed on a clinical PET/MR scanner (Siemens Biograph mMR) were considered. Activity reduction was simulated by truncating the original Full Tracer Activity (FTA) list-mode data correspondingly to tracer activity of 2.4, 1.8, 1.5, 1.2 and 0.6 MBq/kg (Figure). VOIs were defined by two methods: 1) applying a threshold equal to 40% of SUVmax in the FTA image and coping the identified VOIs to low-activity images (Fixed VOIs); 2) thresholding in each image (Variable VOIs). SUV were discretized in two ways: 1) resampling to 64 levels (R64); 2) rounding to 0.25 (R025). Ninety-one features (36 first order and 55 higher-order statistics) were extracted using IBEX (v.1.0 β ) . To assess features stability for each metric, relative changes from FTA images were computed and paired t-tests were performed. Results Differences in features changes at lower activity levels were found between VOI contouring (Fixed VOIs vs Variable VOIs) and SUV resampling (R64 vs R025) methods. Considering Fixed VOIs and R64 resampling, 52/91 features showed non-statistically significant differences for all activity levels. Focusing on metrics as robust as SUVmax and SUVpeak to changes in voxel size and FWHM of the gaussian filter [1] , the effects of decreasing tracer activity are quantitatively variable (Table). Conclusions Selected PET radiomic features can provide reliable information of tumor heterogeneity for low-activity pediatric protocols depending on SUV resampling and lesion delineation strategies.

Purpose The evaluation of features robustness in respect to image acquisition and post-processing parameters changes is fundamental for radiomic studies, especially in the case of multi-institutions collaborations. In this study the sensibility of PET radiomic features to tracer activity reduction in PET/MRI pediatric examinations was investigated in detail. The use of different SUV resampling and contouring strategies was also assessed. Methods Twenty-one whole-body 18F-FDG-PET/MRI pediatric examinations performed on a clinical PET/MR scanner (Siemens Biograph mMR) were considered. To simulate activity reduction, the full tracer activity (FTA) list-mode data (3 MBq/kg, 5 min/bed position) were truncated corresponding to decreasing activities (2.4, 1.8, 1.5, 1.2 and 0.6 MBq/kg). Fifty-six lesions were detected. Two methods of VOI definition have been employed: 1) using a threshold equal to 40% of SUVmax in the FTA image and copying the identified VOIs to low-activity images (Fixed VOIs); 2) thresholding at 40% of SUVmax in each image (Variable VOIs). To reduce noise, images were pre-processed discretizing lesion SUV in two different ways: 1) resampling to 64 levels (R64); 2) rounding to 0.25 (R025). Fifty-five texture features were extracted using IBEX (v.1.0 β ) . To assess features robustness, for each metric and reduced activity level, relative changes from FTA image, paired Wilcoxon tests and Intraclass Correlation Coefficient (ICC) were computed taking FTA features values as the ground truth. SUVmean was computed in the lesions at each activity level and its average relative changes from FTA were considered as benchmarks for texture features stability. Results The choice of contouring and SUV resampling methods results in different features changes at lower activity levels from FTA. Focusing on Variable VOI and R025, at 1.5 MBq/kg, 35/55 features showed both non-statistically significant differences from FTA image (paired Wilcoxon test, p-value 0.01) and ICC > 0.85. At lowest activities (1.5, 1.2, 0.6 MBq/kg), about half of the features changed from FTA values less than the corresponding SUVmean changes (2%, 3%, 9%) using Variable VOI-R025. Conclusions Specific PET texture features can be reliably extracted from low-activity images in pediatrics for tumor biologic heterogeneity characterization depending on tracer activity level, SUV resampling and lesion delineation strategies.

Introduction The Abdus Salam International Centre for Theoretical Physics (ICTP) and the Trieste University have initiated in 2014 a Master of Advanced Studies in Medical Physics a two-years training programme in Medical Physics. The programme is designated to provide young promising graduates in physics, mainly from developing countries, with a post-graduated theoretical and clinical training suitable to be recognised as Clinical Medical Physicist in their countries. Presently, the 3 cycles of the programme has seen 49 participants from 33 Countries: Africa (19), Asia (11), Central and South America (14), and Europe (5), selected from more than 400 applicants per year. Scholarships are awarded to candidates from developing countries with support of the IAEA, TWAS, KFAS, IOMP, EFOMP and ICTP. Material and methods The programme is developed following the recommendations of IOMP and IAEA for education and clinical training. In the first year 332 lectures and 228 h of exercises are devoted to all main fields of medical physics. The second year is spent in one of the 12 medical physics department of the hospitals’ network for the clinical training in: radiation oncology or diagnostic and nuclear medicine, on a programme developed adapting the IAEA (TCS37, TCS47 and TCS50) and AFRA guidelines. Conclusions IOMP, EFOMP and IAEA are seeing this initiative as an answer to the growing demand of Medical Physicists in developing Countries, representing an important European contribution to the development of medical physics in the developing world.

Purpose To evaluate the performance characteristic of Philips Ingenuity TF PET/CT system with the new Pixelar detector design. A comparison of different image reconstruction protocols for EARL accreditation programme was performed. Methods Performance measurements on PET scanner were performed according to the NEMA NU2-2012 standard. Image quality was extended by accounting for different reconstruction parameters (frame timing, PSF iteration number, PSF regularization). A NEMA Image quality phantom was used for suitable image reconstruction protocol evaluation, according to EARL guideline. Performance measurements on CT scanner were performed according to IAEA No.19 publication. Geometrical efficiency was evaluated by exposure of various beam collimations on radiochromic films. Image quality parameters (MTF, Noise) using all reconstruction filters and iterative reconstruction (IDose) were obtained by Catphan®600 acquisitions. Influence of current modulation on patient dose (DoseRight) was studied using an anthropomorphic phantom. Results Spatial resolutions ranged from 4.6 mm at 1 cm to 6.0 mm at 20 cm. Sensitivity measured in the centre and at 10 cm were 7.58 and 7.43 cps/kBq, respectively. The measured NECR peak was 122.7 kcps at 20.3 kBq/cm3. The scatter fraction was 36.6%. Results of image quality test are reported in table. Manufacturer’s EARL dedicated reconstruction protocol did not perfectly meet accreditation requirements as others reconstructions with PSF. CT acceptance parameters met manufacturers and international guidelines specifications, except from geometrical efficiencies for 5 mm, 2.5 mm and 1 mm beam collimations. Decreasing DoseRight index from 26 to 24 and 16, dose reductions of 19.8% and 67.3% were observed. Conclusions Philips Ingenuity TF PET/CT system has overall good performance characteristics, comparable with similar scanners from other manufacturers. The CT part performance meets manufacturer’s specifications with some discrepancies, which do not have a significant impact on clinical use. Regarding EARL accreditation programme, a better adjustment of reconstruction protocol is needed.

Purpose To use a specific Phyton script for automatic optimization process in RayStation treatment planning system (TPS) in the head and neck treatments. Comparison with different commercial automatic planning is reported. Methods Genetic algorithm (GA) was implemented for head and neck VMAT treatments. The chromosomes of the algorithm were max equivalent uniform dose functions (maxEUD) for: larynx, oral cavity and both parotid glands. Ten initial couples were randomly generated and a maximum of five reproductions were permitted. The script was tested for fifteen patients in three different centres: some patients had three dose levels (70 Gy, 63 Gy and 54 Gy) in 35 fractions, others had two levels (69.96 Gy, 60 Gy) in 32 fractions. A comparison with corresponding plans created with Monaco TPS (M, Elekta), MCO option of RayStation (MCO, RaySearch) and RapidPlan (RP, Varian) was carried out. All the plans were evaluated with a score of PlanIQ (Sun Nuclear) in terms of target coverage, conformity index of PTVs and constraints of OARs. Results In figure are reported the totals scores (TS) obtained. Script plans scores were always higher than RP and M (mean TS: 80.0 ± 9.1 for GA and 72.2 ± 9.1 for RP, 77.3 ± 13.9 for GA and 74.2 ± 14.2 for M). PTVs coverage, Maximum doses of spinal cord and brainstem were always below the requested value for all tested systems. For parallel OARs, GA spared parotid glands more than RP (average score of one parotid gland: 81.0 ± 15.0 for GA and 45.0 ± 10.0 for RP); GA spared also Larynx more than MCO (average score 78.0 ± 9.0 for GA and 29.0 ± 12.0 for MCO). For other OARs, the results obtained with GA, RP and MCO were similar. Conclusions GA gives results clinically comparable with automatic commercial systems. These preliminary results must be confirmed with a larger Head and Neck plans dataset [1] .

Purpose This study measured the reduction in human-caused variability driven by the use of RapidPlan (Varian Medical Systems, Palo Alto, CA). Methods Seven planners, with different levels of planning experience, were asked to deliver a VMAT treatment for fifteen prostate cancer patients with and without RapidPlan assistance. The plans were compared on the basis of target coverage, conformance and sparing of rectum, bladder and femnoral heads. The Plan Quality Metric formalism was used as an overall measure of plan quality. Inter-planner and intra-planner variability were measured in terms of differences in mean values and InterQuartile Ranges patients and operators. Results Target coverage, homogeneity, conformance and bladder sparing were similar between manual and RapidPlan assisted plans. But, the latter showed increased sparing of rectum and femoral heads sparing. 8 out of 15 patients showed a statistically significant increase in overall quality, as measured by percentage PQM%. RapidPlan assistance induces a reduction in inter-planner variability for rectum and femoral heads (p-value RapidPlan assistance induced a reduction of the variability of the overall plan quality, as a result of a large increase in plan quality for the less experienced planners. In general the inter-planner, IQR of PQM%, was reduced from 8.32 ± 4.19 to 4.73 ± 3.79 (p-value = 0.0046). At the same time, a reduction in intra-planner variability is measured with a significant overall reduction (p-value = 0.033). Conclusions The assistance of RapidPlan during the optimization of prostate cancer treatments induces a significant increase of plan quality and a contextual reduction of plan variability. RapidPlan is proven to be a valuable tool to leverage the planning skills of less experienced planners ensuring a better homogeneity of treatment plan quality.

Purpose This study is aimed to implement and validate a free Monte Carlo system (GMctdospp) for dose calculation in CT scans. Methods GMctdospp is an open source software developed by Institute of Medical Physics and Radiation Protection [1] . It can be downloaded and installed on a local server, to perform dosimetric calculations from CT images. Model of the CT equipment used for measurements (Siemens Somatom Definition AS) was provided within the software. The CT number to density calibration curve was introduced in the configuration data, to accurately match the HU ranges of simulated materials. Dose values at center and peripheral positions of a CTDI head phantom were measured with a pencil ionization chamber for different beam collimations (5 mm–10 mm–14.4 mm–19.2 mm), and compared to those simulated by the MC software. To define volumes for dose calculation, VOIs were obtained in the CT images by contouring the sensitive volume of the detector. In order to provide an estimation for skin dose, a second set of measurements was performed by scanning the head of a Rando phantom with gafchromic films placed on its surface in different positions (nose, occipital zone, temporal left and right). Images were acquired with a standard helical head routine protocol (120 kV, 19.2 mm collimation) and fixed tube current (200 mA). Dose values measured by the gafchromic films were then compared to those resulting from MC simulations based on the acquired CT images. Results The accuracy of the MC simulated dose values was variable. For CTDI head phantom, the difference between measured and simulated dose ranged between 2% and 19%. For skin dose an average agreement of about 13% was found between measured and calculated values. Conclusions Gmctdospp free MC software can be effectively used to calculate absorbed dose in CT scans acquired with fixed mA. Given the variability we observed in accuracy of the simulated dose values, further work is required in our institution, in order to validate the MC software.

The Abdus Salam International Centre for Theoretical Physics (ICTP) and the Trieste University have initiated in 2014 a Master of Advanced Studies in Medical Physics (www.ictp.it/programmes/mmp.aspx), a two-years training programme in Medical Physics, co- sponsored by the Academy of Sciences for the Developing World (TWAS).

Purpose To establish the reliability and accuracy of a UNIQUE Linac in delivering RapidArc treatments and assess its long term stability. Materials and methods UNIQUE performance was monitored and analyzed for a period of nearly two years. 2280 Dynalog files, related to 179 clinical RapidArc treatments were collected. Different tumor sites and dose scheduling were included, covering the full range of our treatment plans. Statistical distributions of MLC motion error, gantry rotation error and MU delivery error were evaluated. The stochastic and systematic nature of each error was investigated together with their variation in time. Results All the delivery errors are found to be small and more stringent tolerances than those proposed by TG142 are suggested. Unlike MLC positional errors, where a linear relationship with leaf speed holds, other Volumetric Modulated Arc Therapy (VMAT) parameters reveal a random nature and, consequently, a reduced clinical relevance. MLC errors are linearly related only to leaf speed no matter the shape of the MLC apertures. Gantry rotation and MU delivery are as accurate as major competing Linacs. UNIQUE was found to be reliable and accurate throughout the investigation period, regardless of the specific tumor sites and fractionation schemes. Conclusions The accuracy of RapidArc treatments delivered with UNIQUE has been established. The stochastic nature of delivery errors is proven. Long term statistics of the delivery parameter errors do not show significant variations, confirming the reliability of the VMAT delivery system.

The aim of the present work was the validation of the VMC ++ Monte Carlo (MC) engine implemented in the Oncentra Masterplan (OMTPS) and used to calculate the dose distribution produced by the electron beams (energy 5-12 MeV) generated by the linear accelerator (linac) Primus (Siemens), shaped by a digital variable applicator (DEVA). The BEAMnrc/DOSXYZnrc (EGSnrc package) MC model of the linac head was used as a benchmark. Commissioning results for both MC codes were evaluated by means of 1D Gamma Analysis (2%, 2 mm), calculated with a home-made Matlab (The MathWorks) program, comparing the calculations with the measured profiles. The results of the commissioning of OMTPS were good [average gamma index ( γ ) > 97%]; some mismatches were found with large beams (size ≥ 15 cm). The optimization of the BEAMnrc model required to increase the beam exit window to match the calculated and measured profiles (final average γ > 98%). Then OMTPS dose distribution maps were compared with DOSXYZnrc with a 2D Gamma Analysis (3%, 3 mm), in 3 virtual water phantoms: (a) with an air step, (b) with an air insert, and (c) with a bone insert. The OMTPD and EGSnrc dose distributions with the air-water step phantom were in very high agreement (γ ∼ 99%), while for heterogeneous phantoms there were differences of about 9% in the air insert and of about 10–15% in the bone region. This is due to the Masterplan implementation of VMC ++ which reports the dose as “dose to water”, instead of “dose to medium”.

Background: Rapid and user-friendly software tools for individual estimates of organ doses in CT are of the utmost importance to support the professionals in the choice of the appropriate imaging modalities. Most CT-dosimetry tools, like CT Expo [1], CT Dosimetry [2], as well as a new dosimetry tool [3], rely on the assumption that organ doses estimated for one CT scanner can be converted to other CT scanner using the ratio of the Computed Tomography Dose Index (CTDI) between two CT scanners. We tested this assumption for paediatric patients using physical phantom measurements for various protocols and CT scanners. Measurements were compared with dosimetry tools. Materials and methods: Dose to 22 radiosensitive organs were measured using thermoluminescence dosimeters inserted within an anthropomorphic 5-year old phantom. Dose measurements were performed for wholebody scans on 4 scanner models from the 4 major manufacturers (Siemens, GE, Philips and Toshiba); both axial and helical modes were tested with small collimations (below 12 mm). Measured doses were compared with the results of Monte-Carlo simulations [3]. Results: Whereas the measured organ doses showed important variability across the different scanner models, doses normalised to CTDI showed significantly less variation. Higher tube voltage also showed less variation. The simulated organ doses reasonably compared with the measurements. For example, at 120 kV in axial mode with 10 mm collimation, the mean coefficient of variation between the scanner models was below 10%; the relative difference between measured and simulated organ doses was within ±15% for most organs. Discussion: For the tested collimations (below 12 mm), both in axial and helical modes, the CTDI fairly accounts for the difference in CT design across different models. Further measurements are being carried out to test the algorithm against protocols more representative of the clinical practice. This study proved that, for small collimations and paediatric patients, organ doses simulated from one CT scanner can be converted to other CT scanners using CTDI-ratio. Those results are of interest for fast dose assessment and retrospective dosimetry studies. Acknowledgments: These measurements were performed within the framework of the EPI-CT study, supported by the European Community's Seventh Framework Programme (FP7/2007e2013) under grant agreement number 269912-EPI-CT: Epidemiological study to quantify risks for paediatric computerized tomography and to optimise doses.