Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
J Radiat Res. 2011;52(1):59-68. doi: 10.1269/jrr.10062. Epub 2010 Dec 13.
The RBE-weighted absorbed dose, called "biological dose," has been routinely used for carbon-ion treatment planning in Japan to formulate dose prescriptions for treatment protocols. This paper presents a microdosimetric approach to measuring the biological dose, which was redefined to be derived from microdosimetric quantities measured by a tissue-equivalent proportional counter (TEPC). The TEPC was calibrated in (60)Co gamma rays to assure a traceability of the TEPC measurement to Japanese standards and to eliminate the discrepancies among matching counters. The absorbed doses measured by the TEPC were reasonably coincident with those measured by a reference ionization chamber. The RBE value was calculated from the microdosimetric spectrum on the basis of the microdosimetric kinetic model. The biological doses obtained by the TEPC were compared with those prescribed in the carbon-ion treatment planning system. We found that it was reasonable for the measured biological doses to decrease with depth around the rear SOBP region because of beam divergence, scattering effect, and fragmentation reaction. These results demonstrate that the TEPC can be an effective tool to assure the radiation quality in carbon-ion radiotherapy.
RBE 加权吸收剂量，称为“生物剂量”，已在日本常规用于碳离子治疗计划，以制定治疗方案的剂量处方。本文提出了一种微观剂量学方法来测量生物剂量，该剂量被重新定义为源自组织等效比例计数器 (TEPC) 测量的微观剂量学数量。TEPC 在 (60)Co 伽马射线下进行校准，以确保 TEPC 测量与日本标准的可追溯性，并消除匹配计数器之间的差异。TEPC 测量的吸收剂量与参考电离室测量的吸收剂量相当吻合。根据微剂量动力学模型，从微剂量谱计算出 RBE 值。TEPC 获得的生物剂量与碳离子治疗计划系统中规定的剂量进行了比较。我们发现，由于束发散、散射效应和碎裂反应，后 SOBP 区域周围的测量生物剂量随深度降低是合理的。这些结果表明，TEPC 可以成为确保碳离子放射治疗中辐射质量的有效工具。
