Tamura Mikoto, Komori Masataka, Oguchi Hiroshi, Iwamoto Yasushi, Rachi Toshiya, Ota Kenji, Hemmi Atsushi, Shimozato Tomohiro, Obata Yasunori
Department of Radiological Sciences, Graduate School of Medicine, Nagoya University, 1-1-20 Daiko-Minami, Higashi-ku, Nagoya, Aichi, Japan.
Radiol Phys Technol. 2013 Jul;6(2):415-22. doi: 10.1007/s12194-013-0214-5. Epub 2013 Apr 25.
In carbon-ion radiotherapy, it is important to evaluate the biological dose because the relative biological effectiveness values vary greatly in a patient's body. The microdosimetric kinetic model (MKM) is a method of estimating the biological effect of radiation by use of microdosimetry. The lateral biological dose distributions were estimated with a modified MKM, in which we considered the overkilling effect in the high linear-energy-transfer region. In this study, we used the Monte Carlo calculation of the Geant4 code to simulate a horizontal port at the Heavy Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences. The lateral biological dose distributions calculated by Geant4 were almost flat as the lateral absorbed dose in the flattened area. However, in the penumbra region, the lateral biological dose distributions were sharper than the lateral absorbed dose distributions. Furthermore, the differences between the lateral absorbed dose and biological dose distributions were dependent on the depth for each multi-leaf collimator opening size. We expect that the lateral biological dose distribution presented here will enable high-precision calculations for a treatment-planning system.
在碳离子放射治疗中，评估生物剂量很重要，因为相对生物效能值在患者体内差异很大。微剂量动力学模型（MKM）是一种通过微剂量学来估算辐射生物效应的方法。我们使用改进的MKM估算横向生物剂量分布，其中考虑了高线性能量转移区域的过杀伤效应。在本研究中，我们利用Geant4代码的蒙特卡罗计算来模拟日本国立放射科学研究所千叶重离子医学加速器的水平射野。Geant4计算得到的横向生物剂量分布在平坦区域与横向吸收剂量几乎一样平坦。然而，在半影区，横向生物剂量分布比横向吸收剂量分布更陡峭。此外，横向吸收剂量与生物剂量分布之间的差异取决于每个多叶准直器开口尺寸对应的深度。我们期望这里给出的横向生物剂量分布能够为治疗计划系统实现高精度计算。
