Out‐of‐field organs are not commonly designated as dose calculation targets during radiation therapy treatment planning, but they might entail risks of second cancer. Risk components include specific internal body scatter, which is a dominant source of out‐of‐field doses, and head leakage, which can be reduced by external shielding. Our simulation study quantifies out‐of‐field organ doses and estimates second cancer risks attributable to internal body scatter in whole‐breast radiotherapy (WBRT) with or without additional regional nodal radiotherapy (RNRT), respectively, for right and left breast cancer using Monte Carlo code PHITS. Simulations were conducted using a complete whole‐body female model. Second cancer risk was estimated using the calculated doses with a concept of excess absolute risk. Simulation results revealed marked differences between WBRT alone and WBRT plus RNRT in out‐of‐field organ doses. The ratios of mean doses between them were as large as 3.5–8.0 for the head and neck region and about 1.5–6.6 for the lower abdominal region. Potentially, most out‐of‐field organs had excess absolute risks of less than 1 per 10,000 persons‐year. Our study surveyed the respective contributions of internal body scatter to out‐of‐field organ doses and second cancer risks in breast radiotherapy on this intact female model.

中文翻译：

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对于每个场外器官，使用蒙特卡罗代码结合体内散射，计算和估算乳腺癌放疗的第二次癌症风险

在放射治疗治疗计划中，通常不将野外​​器官指定为剂量计算目标，但它们可能会引发第二次癌症。危险因素包括特定的内部身体散射（是场外剂量的主要来源）和头部泄漏（可通过外部屏蔽来减少）。我们的模拟研究量化了野外器官剂量，并估计了使用Monte疗法对右乳腺癌和左乳腺癌分别进行全乳放疗（WBRT）和有或无局部淋巴结放疗（RNRT）时由体内散布引起的第二种癌症风险卡洛代码PHITS。使用完整的全身女性模型进行了模拟。使用计算的剂量和绝对绝对风险的概念来估计第二次癌症风险。模拟结果表明，单独的WBRT和WBRT加RNRT在野外器官剂量方面存在显着差异。头颈部区域的平均剂量比例高达3.5–8.0，下腹部区域的平均剂量比例约为1.5–6.6。潜在的是，大多数野外器官的绝对绝对风险都超过每10,000人每年1次。我们的研究调查了在这种完好无损的女性模型上，体内散布对野外器官剂量和继发乳腺癌风险的各自贡献。