Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba-shi, Chiba 263-8555, Japan.
J Radiat Res. 2011;52(6):789-96. doi: 10.1269/jrr.11044. Epub 2011 Sep 16.
Cerebral radionecrosis is a significant side effect in radiotherapy for brain cancer. The purpose of this study is to calculate the relative biological effectiveness (RBE) of carbon-ion beams on brain cells and to show RBE-weighted dose distributions for cerebral radionecrosis speculation in a carbon-ion treatment planning system. The RBE value of the radionecrosis for the carbon-ion beam is calculated by the modified microdosimetric kinetic model on the assumption of a typical clinical α/β ratio of 2 Gy for cerebral radionecrosis in X-rays. This calculation method for the RBE-weighted dose is built into the treatment planning system for the carbon-ion radiotherapy. The RBE-weighted dose distributions are calculated on computed tomography (CT) images of four patients who had been treated by carbon-ion radiotherapy for astrocytoma (WHO grade 2) and who suffered from necrosis around the target areas. The necrotic areas were detected by brain scans via magnetic resonance imaging (MRI) after the treatment irradiation. The detected necrotic areas are easily found near high RBE-weighted dose regions. The visual comparison between the RBE-weighted dose distribution and the necrosis region indicates that the RBE-weighted dose distribution will be helpful information for the prediction of radionecrosis areas after carbon-ion radiotherapy.
脑放射性坏死是脑癌放射治疗的一个严重副作用。本研究的目的是计算碳离子束对脑细胞的相对生物效应（RBE），并在碳离子治疗计划系统中显示用于推测脑放射性坏死的 RBE 加权剂量分布。假设 X 射线中脑放射性坏死的典型临床 α/β 比为 2 Gy，通过修正的微剂量动力学模型计算碳离子束的放射性坏死的 RBE 值。该 RBE 加权剂量的计算方法被构建到碳离子放射治疗的治疗计划系统中。在已经接受碳离子放射治疗的 4 名星形细胞瘤（WHO 分级 2 级）患者的 CT 图像上计算 RBE 加权剂量分布，这些患者在靶区周围发生了坏死。在治疗照射后，通过磁共振成像（MRI）对脑扫描检测到坏死区域。检测到的坏死区域很容易在高 RBE 加权剂量区域附近找到。RBE 加权剂量分布与坏死区域之间的直观比较表明，RBE 加权剂量分布将有助于预测碳离子放射治疗后的放射性坏死区域。
