Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy.
Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy.
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DOI：
10.1118/1.4870980
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发表时间：
2013-07
期刊：
影响因子：
3.8
通讯作者：
N. Kanematsu;Y. Koba;R. Ogata;T. Himukai
中科院分区：
文献类型：
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作者：
N. Kanematsu;Y. Koba;R. Ogata;T. Himukai
最近的一项研究表明，由于核相互作用中的成分差异，聚乙烯（PE）会导致每射程偏移0.45%/cm的额外碳离子衰减。本研究旨在评估PE距离补偿器对碳离子放射治疗中肿瘤剂量的影响。方法碳离子辐射模型由初级碳离子和次级粒子组成，在布拉格峰扩展的中间肿瘤深度处，分别估算初级碳离子和次级碳离子的剂量和相对生物学效应（RBE）。假设这些成分的衰减和产率随深度呈指数行为，计算了临床碳离子束的PE对剂量的影响，并通过实验进行了部分测试。将双组分模型整合到治疗计划系统中，并在两个临床病例中估计PE效应。结果PE的单位距离移动衰减在剂量上为0.1%-0.3%/cm，在RBE加权剂量上为0.2%-0.4%/cm，取决于能量和距离调制宽度。在极端情况下，这意味着RBE加权剂量减少高达3%。然而，在治疗计划研究中，对肿瘤的RBE加权剂量的影响通常在1%的减少范围内。结论PE中初级碳离子的额外衰减部分被肿瘤剂量增加的次级粒子所补偿。在实际情况下，与治疗计划、患者设置、射束输送和临床响应中的固有不确定性相比，PE范围补偿器通常仅会引起边际误差。
PURPOSE A recent study revealed that polyethylene (PE) would cause extra carbon-ion attenuation per range shift by 0.45%/cm due to compositional differences in nuclear interactions. The present study aims to assess the influence of PE range compensators on tumor dose in carbon-ion radiotherapy. METHODS Carbon-ion radiation was modeled to be composed of primary carbon ions and secondary particles, for each of which the dose and the relative biological effectiveness (RBE) were estimated at a tumor depth in the middle of spread-out Bragg peak. Assuming exponential behavior for attenuation and yield of these components with depth, the PE effect on dose was calculated for clinical carbon-ion beams and was partly tested by experiment. The two-component model was integrated into a treatment-planning system and the PE effect was estimated in two clinical cases. RESULTS The attenuation per range shift by PE was 0.1%-0.3%/cm in dose and 0.2%-0.4%/cm in RBE-weighted dose, depending on energy and range-modulation width. This translates into reduction of RBE-weighted dose by up to 3% in extreme cases. In the treatment-planning study, however, the effect on RBE-weighted dose to tumor was typically within 1% reduction. CONCLUSIONS The extra attenuation of primary carbon ions in PE was partly compensated by increased secondary particles for tumor dose. In practical situations, the PE range compensators would normally cause only marginal errors as compared to intrinsic uncertainties in treatment planning, patient setup, beam delivery, and clinical response.