Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Nuclear Science and Technology Research Institute, Tehran, Iran.
Appl Radiat Isot. 2022 Jun;184:110188. doi: 10.1016/j.apradiso.2022.110188. Epub 2022 Mar 16.
Radiotherapy is one of the most common methods for treating malignant diseases, whose ultimate goal is to deliver lethal doses to tumor cells. One of the unwanted consequences of radiotherapy is secondary radiation outside the treatment field, which imposes additional doses to healthy tissues and organs, specifically neutron doses, which we aim to evaluate. Therefore, this study aims to measure the fast neutron equivalent dose and the risk of secondary cancer in the thyroid, chiasm, and lenses in the treatment of the pelvic area. In this study, CR-39 detectors were used to measure the equivalent fast neutron dose in different sections of the RANDO Phantom (thyroid, chiasm, and lenses) and were irradiated by the energy of 18 MV on Varian Clinac 2100 C-D linear accelerator. CR-39 detectors were calibrated with predetermined doses by an Am-Be neutron source. Then, after etching and reading processes, the equivalent dose of fast neutrons was determined. According to the results, the fast neutron doses in the thyroid, right and left eye lenses, and chiasm were 0.613 ± 0.024, 0.835 ± 0.040, 0.866 ± 0.016, and 0.685 ± 0.045 mSv/Gy, respectively. Moreover, the secondary cancer risks in the unshielded organs are 0.004, 0.029, 0.030, and 0.025 for the thyroid, right and left eye lenses, and chiasm, respectively. In conclusion, the contribution of neutrons to the secondary doses in the out-of-field organs is significant and should not be ignored.
放射治疗是治疗恶性疾病最常用的方法之一，其最终目标是向肿瘤细胞输送致死剂量。放射治疗的一个不良后果是治疗场以外的二次辐射，这会对健康组织和器官造成额外的剂量，特别是中子剂量，我们旨在评估这些剂量。因此，本研究旨在测量盆腔区域治疗中甲状腺、视交叉和晶状体的快中子当量剂量和继发癌症风险。在这项研究中，使用 CR-39 探测器测量 RANDO 体模（甲状腺、视交叉和晶状体）不同部位的快中子当量剂量，并在瓦里安 Clinac 2100C-D 线性加速器上用 18MV 的能量进行照射。CR-39 探测器用 Am-Be 中子源进行了预定剂量的校准。然后，经过蚀刻和读数过程，确定了快中子的当量剂量。结果表明，甲状腺、右眼晶状体、左眼晶状体和视交叉的快中子剂量分别为 0.613±0.024、0.835±0.040、0.866±0.016 和 0.685±0.045mSv/Gy。此外，未屏蔽器官的继发癌症风险分别为甲状腺、右眼晶状体、左眼晶状体和视交叉的 0.004、0.029、0.030 和 0.025。总之，中子对场外器官二次剂量的贡献是显著的，不容忽视。
