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INTRODUCTION: Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) are the main radiotherapy techniques for treating and managing rectal cancer. Collimator rotation is one of the crucial parameters in radiotherapy planning, and its alteration can cause dosimetric variations. This study assessed the effect of collimator rotation on the dosimetric results of various IMRT and VMAT plans for rectal cancer. MATERIALS AND METHODS: Computed tomography (CT) images of 20 male patients with rectal cancer were utilized for IMRT and VMAT treatment planning with various collimator angles. Nine different IMRT techniques (5, 7, and 9 coplanar fields with collimator angles of 0°, 45°, and 90°) and six different VMAT techniques (1 and 2 full coplanar arcs with collimator angles of 0°, 45°, and 90°) were planned for each patient. The dosimetric results of various treatment techniques for target tissue (conformity index [CI] and homogeneity index [HI]) and organs at risk (OARs) sparing (parameters obtained from OARs dose–volume histograms [DVH]) as well as radiobiological findings were analyzed and compared. RESULTS: The 7-fields IMRT technique demonstrated lower bladder doses (V40Gy, V45Gy), unaffected by collimator rotation. The 9-fields IMRT and 2-arcs VMAT (excluding the 90-degree collimator) had the lowest V35Gy and V45Gy. A 90-degree collimator rotation in 2-arcs VMAT significantly increased small bowel and bladder V45Gy, femoral head doses, and HI values. Radiobiologically, the 90-degree rotation had adverse effects on small bowel NTCP (normal tissue complication probability). No superiority was found for a 45-degree collimator rotation over 0 or 30 degrees in VMAT techniques. CONCLUSION: Collimator rotation had minimal impact on dosimetric parameters in IMRT planning but is significant in VMAT techniques. A 90-degree rotation in VMAT, particularly in a 2-full arc technique, adversely affects PTV homogeneity index, bladder dose, and small bowel NTCP. Other evaluated collimator angles did not significantly affect VMAT dosimetrical or radiobiological outcomes. [ABSTRACT FROM AUTHOR]

Introduction: Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) are primary techniques for rectal cancer treatment. In radiotherapy planning, collimator rotation is a crucial parameter, and its adjustments can lead to dosimetric variations. This study examined the influence of collimator rotation on dosimetric outcomes for different IMRT and VMAT plans for rectal cancer. Methods: CT images from 20 male rectal cancer patients were used for IMRT and VMAT treatment planning with varying collimator angles. Nine IMRT techniques (5, 7, and 9 coplanar fields with collimator angles of 0°, 45°, and 90°) and six VMAT techniques (1 and 2 full coplanar arcs with collimator angles of 0°, 45°, and 90°) were planned for each patient. Dosimetric results for target tissue (conformity index [CI] and homogeneity index [HI]) and sparing of organs at risk (OARs) (parameters from OARs dose - volume histograms [DVH]) were analyzed and compared, along with radiobiological findings. Results: The 7-fields IMRT technique showed lower bladder doses (V40Gy, V45Gy) unaffected by collimator rotation. The 9 - fields IMRT and 2 - arcs VMAT (excluding the 90 - degree collimator) exhibited the lowest V35Gy and V45Gy. A 90 - degree collimator rotation in 2 - arcs VMAT significantly increased small bowel and bladder V45Gy, femoral head doses, and HI values. Radiobiologically, the 90 - degree rotation adversely affected small bowel NTCP (normal tissue complication probability). No superiority was observed for a 45 - degree collimator rotation over 0 or 30 degrees in VMAT techniques. Conclusions: Collimator rotation minimally impacted dosimetric parameters in IMRT planning but significantly affected VMAT techniques. A 90 - degree rotation in VMAT, especially in a 2 - full arc technique, negatively impacted PTV homogeneity index, bladder dose, and small bowel NTCP. Other evaluated collimator angles did not significantly affect VMAT dosimetrical or radiobiological outcomes. [ABSTRACT FROM AUTHOR]

Introduction: Radioactive iodine finds widespread application in both diagnostic and therapeutic contexts. I - 123 and I - 125 serve diagnostic purposes, whereas I - 125 and I - 131 are employed for treating conditions such as hyperthyroidism and thyroid tumors, either through targeted radionuclide therapy or brachytherapy. The deterministic impact of the dose received by cells, especially within the cell nucleus, plays a crucial role in predicting radiation complications. This study aims to compare the received dose in cellular human thyroid models resulting from exposure to I - 123, I - 125, and I - 131 radionuclides. Methods: The Gate Monte Carlo software (version 9.3) was used for simulation and dosimetric calculations. The energies of electrons resulting from decay were chosen based on the corresponding decay spectrum of each radionuclide, as provided by MIRD (medical internal radiation dose). The cells were simulated considering cubic geometries with the dimensions of 6, 10, and 17.5 micrometers, and the nucleus was modeled as a spherical shape with diameters of 5, 7, and 9 micrometers. The s - value (dose per decay) values were calculated for different source - target configurations, including nucleus (as source) - nucleus (as target volume), cell membrane - nucleus, and cytoplasm - nucleus. In all cases, the S - values in the extracellular medium, were also calculated. Results: Across all scenarios, the highest S - value was related to the nuclear self - absorption (nucleus - nucleus configuration). I131 had the highest S - value in the nucleus - nucleus situation and the lowest value was for I123. In the case of cytoplasm - nucleus and cellmembrane - nucleus, the highest S value was related to I131. In all cases, the contribution of internal radiation electrons in S - value was higher than Auger and beta electrons. S - value decreased with the increase of cell size and nucleus. This difference was greater in the cytoplasm - nucleus and cell - nucleus membrane than in the nucleus - nucleus situation. It is worth mentioning that I123 delivered a lower dose to the extracellular environment compared to other radionuclides. Conclusions: Distinct radiations of radioactive iodine demonstrated significant differences in their contributions to S - values. The dimensions of the cell exerted a more substantial effect than the source - nucleus location on the delivered dose to the cell nucleus. I123, notably, resulted in a lower dose to the cell nucleus and the extracellular environment, suggesting potentially reduced damage to the thyroid cell DNA. [ABSTRACT FROM AUTHOR]

Aim: To evaluate the dosimetric parameters of level II lymph nodes in chest wall three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) of mastectomy patients using dual-isocentric (DIT) and mono-isocentric techniques (MIT). Materials and methods: Computed tomography (CT) images of 20 mastectomy patients undergoing chest wall external radiotherapy were used as the input data for the abovementioned techniques. Selected dosimetric parameters were calculated for the axillary level I–III lymph nodes, chest wall, heart and lung. Paired t-test statistical analysis was used for comparing the results of MIT and DIT in both 3D-CRT and IMRT methods. Results: There were significant differences in Dmin (minimum dose), Dmax (maximum dose) and maximum–minimum dose between MIT and DIT techniques (13, −8·6, −52·2% differences for Dmin, Dmax and maximum–minimum, respectively) in IMRT. There were also significant differences for Dmean (mean dose), Dmax and maximum–minimum dose (7·8, −11·4, −44·6% differences in Dmean, Dmax and maximum–minimum, respectively) in 3D-CRT (p < 0·05). In addition, there were not any differences in the dosimetric parameters for heart, lung and level I and III lymph nodes. Conclusion: In both 3D-CRT and IMRT methods, level II lymph node dose distribution in MIT was closer to the prescribed dose compared with DIT due to the position of these nodes in the field junction area. To achieve a better dose homogeneity, it could be recommended to use MIT instead of DIT in 3D-CRT and IMRT for mastectomy patients. [ABSTRACT FROM AUTHOR]

Gafchromic films are utilized for two-dimensional dose distribution measurements, especially in radiotherapy. In this study, we investigated a close connection between energy and dose rate of Gafchromic EBT3 films irradiating with 6 MV and Co-60 photon beams over a broad dose range. EBT3 films were exposed to 6 MV and Co-60 photon beams using 4 and 2 Gy/min dose rates over a 10–400 cGy dose range. The films were scanned in red, green, and blue channels to obtain the optical density (OD)–dose curves. The OD–dose curves resulted from three-color scans for different photon energies and dose rates were compared by statistical independent t-test. For the radiations of Co-60 and 6 MV photon beams, the highest correlation was obtained between the 2 and 4 Gy/min dose rates with red and green channels, respectively. Moreover, the red channel had a greater OD response per dose value, following the green and blue channels. There was no significant difference between different photon energies' (Co-60 and 6 MV) and dose rates' (2 and 4 Gy/min) dependence on OD-dose response of EBT3 films over a broad domain of radiation dose, except for different photon energies in the blue channel. Our results revealed that the OD-dose response of EBT3 films is independent on photon energies (Co-60 and 6 MV) and dose rate (2 and 4 Gy/min) in the evaluated dose range (10–400 cGy). Therefore, the EBT3 films are suitable, consistent, and reliable instruments for dose measurements in radiotherapy. [ABSTRACT FROM AUTHOR]

Background: Epidemiological studies show that computed tomography (CT) is one of the main sources of ionizing radiations. Shielding of radiosensitive organs is one of the dose reduction methods. This study aimed to assess the eye lens dose reduction and image quality resulting from the use of radio-protective bismuth shield in brain CT imaging. Methods: Bismuth shields were constructed with two different thicknesses (0.02 and 0.06 cm) and two different geometries including: direct contact with eye (contact setup) and 4 cm above the eye (distant setup). The lens dose was determined using thermo luminescent dosimeter (TLD)-207A chips inside an anthropomorphic head phantom during the CT examinations. Noise, SNR (signal to noise ratio), and CNR (contrast to noise ratio) were calculated to evaluate the image quality. Results: The lens dose reduction was higher using the shield with 0.06 cm thickness and in 'contact setup'. On the other hand, the bismuth shield with the thickness of 0.02 cm and in 'distant setup' had lower dose reduction and better image quality. Conclusions: Bismuth shield with the thickness of 0.02 cm and in 'distant setup' could decrease the lens dose to the acceptable levels, while providing a better image quality in comparison with the contact shield setup and with 0.06 cm thickness. Using the bismuth shield is a simple and low cost method for protecting the eye lens in brain CT scans with conventional scanners especially in low income or developing countries. [ABSTRACT FROM AUTHOR]

Introduction: Idiopathic generalised epilepsy (IGE) refers to a group of epilepsies resulting from the activation of neurons in the whole brain. This study aimed to evaluate the metabolite changes in thalamus as diagnostic biomarkers in IGE patients compared to healthy individuals using magnetic resonance spectroscopy (MRS) technique. Methods: The MRS was performed on 35 IGE patients (26 women and 11 men) with average age of 32 (ranged from 18 to 43) and 35 healthy individuals (13 women and 22 men) with average age of 31 (ranged from 21 to 50) as the control group. The levels of N-acetylaspartate (NAA), creatine (Cr) and choline (Cho) were measured using MRS. The NAA/Cr and NAA/Cho ratios were calculated for all participants. These values were statistically compared using t-test between the groups. Results: The NAA had significant lower values in IGE patients, 9.6 (SD = 0.8) and 9.9 (SD = 0.7) for right and left thalamus, respectively, compared to 10.9 (SD = 0.9) and 10.7 (SD = 0.9) in control group. The Cr values in the left side of thalamus were significantly higher in IGE patients (6.7 [SD = 0.8] versus 5.8 [SD = 0.5]); however, there was no difference in right thalamus. Measurements showed no difference for amounts of Cho between the groups in both sides of thalamus. The NAA/Cr ratio was 1.48 (SD = 0.14) and 1.48 (SD = 0.16) for right and left thalamus, respectively, in IGE patients in comparison with 1.83 (SD = 0.2) and 1.86 (SD = 0.26) in controls. There was no meaningful variation between the NAA/Cho ratio of the right and left thalamus among the groups. Conclusion: Thalamic NAA, Cr and NAA/Cr ratio values in IGE patients showed statistical differences compared to healthy individuals. Evaluating metabolites variations in thalamus using MRS is suggested for differentiating IGE patients from healthy individuals. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to compare the skin dose calculated by treatment planning system (TPS) and measured with thermoluminescent dosimeters (TLDs) in brachytherapy of prostatic cancer to show the skin TLD dosimetry as an appropriate quality assurance procedure for TPS dose calculations., Methods: The skin dose of 15 patients with prostatic cancer treated by high dose rate brachytherapy technique was assessed by two types of TLD dosimeters (GR-200 and TLD-100). The TLDs were placed on the patient's skin at three different points (anterior, left, and right) using five TLDs for each point. The dose values of TLDs and TPS were compared using paired t-test and the percentages of difference were reported., Results: There was a good agreement between TPS calculations and TLDs measurements for both of the GR-200 and TLD-100 dosimeters. The mean skin dose values for anterior, left, and right points were 65.06±21.88, 13.88±4.1, and 10.05±4.39 cGy, respectively, for TPS. These values were 65.70±23.2, 14.51±4.3, and 10.54±5 cGy for GR-200, and 64.22±23.5, 13.43±4.4, and 9.99±4.1 cGy for TLD-100, respectively., Conclusion: The TPS skin dose calculations in brachytherapy of prostatic cancer had a good agreement with the TLD-100 and GR-200 measurements at the three different points on patients' skin. TLD-100 had lower differences with TPS calculations compared to GR-200., Relevance for Patients: The outcome of this research shows that for people with prostatic cancer, TPS can estimate accurately the skin dose of different points including anterior, left, and right in brachytherapy technique., Competing Interests: The authors declare no conflicts of interest., (Copyright: © Whioce Publishing Pte. Ltd.)