Yonai Shunsuke, Arai Chinatsu, Shimoyama Kaoru, Fournier-Bidoz Nathalie
Department of Accelerator and Medical Physics, National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology, Anagawa, Inage-ku, Chiba, Japan.
Department of Physics, Toho University, Miyama, Funabashi, Japan.
Radiat Prot Dosimetry. 2018 Aug 1;180(1-4):314-318. doi: 10.1093/rpd/ncy006.
Radiochromic film is a very useful tool for 2D dosimetric measurements in radiotherapy because it is self-developing and has very high-spatial resolution. However, considerable care has to be taken in ion beam radiotherapy owing to the quenching effect of high-linear energy transfer (LET) radiation. In this study, the dose responses of GAFchromic EBT3 and EBT-XD films were experimentally investigated using the clinical carbon ion beam at the Heavy Ion Medical Accelerator in Chiba. Results showed that the relations between absorbed dose and net optical density could be expressed well using an equation proposed by Reinhardt (2015). The quenching effect was evaluated by determining their relative efficiencies for photon irradiation as a function of LET. A correction equation derived in this study allowed the absorbed dose to be determined in the small irradiation field used for carbon ion radiotherapy eye treatments. This study contributes to establishing an absolute dosimetry procedure for heavy ion beams using radiochromic film.
放射变色薄膜是放射治疗中二维剂量测量的一种非常有用的工具，因为它能自行显影且具有非常高的空间分辨率。然而，由于高线性能量转移（LET）辐射的猝灭效应，在离子束放射治疗中必须格外小心。在本研究中，使用千叶重离子医学加速器的临床碳离子束对GAFchromic EBT3和EBT-XD薄膜的剂量响应进行了实验研究。结果表明，吸收剂量与净光密度之间的关系可以用Reinhardt（2015年）提出的方程很好地表示。通过确定它们作为LET函数的光子照射相对效率来评估猝灭效应。本研究推导的校正方程可用于确定碳离子放射治疗眼部时所用小照射野中的吸收剂量。本研究有助于建立使用放射变色薄膜的重离子束绝对剂量测定程序。
