Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
School of Paramedicine, Bushehr University of Medical Sciences, Bushehr, Iran.
PLoS One. 2022 Jul 29;17(7):e0271028. doi: 10.1371/journal.pone.0271028. eCollection 2022.
Neutron contamination as a source of out-of-field dose in radiotherapy is still of concern. High-energy treatment photons have the potential to overcome the binding energy of neutrons inside the nuclei. Fast neutrons emitting from the accelerator head can directly reach the patient's bed. Considering that modern radiotherapy techniques can increase patient survival, concerns about unwanted doses and the lifetime risk of fatal cancer remain strong or even more prominent, especially in young adult patients. The current study addressed these concerns by quantifying the dose and risk of fatal cancer due to photo-neutrons for glioma patients undergoing 18-MV radiotherapy. In this study, an NRD model rem-meter detector was used to measure neutron ambient dose equivalent, H*(10), at the patient table. Then, the neutron equivalent dose received by each organ was estimated concerning the depth of each organ and by applying depth dose corrections to the measured H*(10). Finally, the effective dose and risk of secondary cancer were determined using NCRP 116 coefficients. Evidence revealed that among all organs, the breast (0.62 mSv/Gy) and gonads (0.58 mSv/Gy) are at risk of photoneutrons more than the other organs in such treatments. The neutron effective dose in the 18-MV conventional radiotherapy of the brain was 13.36 mSv. Among all organs, gonads (6.96 mSv), thyroid (1.86 mSv), and breasts (1.86 mSv) had more contribution to the effective dose, respectively. The total secondary cancer risk was estimated as 281.4 cases (per 1 million persons). The highest risk was related to the breast and gonads with 74.4 and, 34.8 cases per 1 million persons, respectively. Therefore, it is recommended that to prevent late complications (secondary cancer and genetic effects), these organs should be shielded from photoneutrons. This procedure not only improves the quality of the patient's personal life but also the healthy childbearing in the community.
中子污染作为放射治疗中的场外剂量源仍然令人担忧。高能治疗光子有潜力克服原子核内中子的结合能。从加速器头发出的快中子可以直接到达患者的病床。考虑到现代放射治疗技术可以提高患者的生存率，对不必要剂量和致命癌症的终生风险的担忧仍然强烈，甚至更加突出，尤其是在年轻成年患者中。本研究通过量化接受 18-MV 放射治疗的胶质瘤患者因光中子引起的致命癌症的剂量和风险来解决这些问题。在这项研究中，使用 NRD 模型 rem-meter 探测器测量患者治疗台上的环境中子剂量当量 H*(10)。然后，根据每个器官的深度和对测量的 H*(10)进行的深度剂量修正，估计每个器官接收到的中子等效剂量。最后，使用 NCRP 116 系数确定有效剂量和继发癌症的风险。证据表明，在所有器官中，在这种治疗中，乳房（0.62 mSv/Gy）和性腺（0.58 mSv/Gy）比其他器官更容易受到光中子的影响。在 18-MV 常规脑部放射治疗中，中子的有效剂量为 13.36 mSv。在所有器官中，性腺（6.96 mSv）、甲状腺（1.86 mSv）和乳房（1.86 mSv）对有效剂量的贡献最大。总继发癌症风险估计为 281.4 例（每 100 万人）。最高风险与乳房和性腺有关，分别为每 100 万人 74.4 例和 34.8 例。因此，建议为了防止晚期并发症（继发癌症和遗传效应），应将这些器官屏蔽免受光中子的影响。这一程序不仅提高了患者个人生活的质量，还有助于社区中健康的生育。
