Shigematsu N, Ito H, Kubo A, Dokiya T
Department of Radiology, Keio University School of Medicine.
Nihon Igaku Hoshasen Gakkai Zasshi. 1996 Jul;56(8):599-604.
The need of radiation therapy in cancer treatment is increasing, however, the dose of radiation is limited by its late effects on normal tissues. Hyperfractionated radiotherapy was applied to patients with various kinds of carcinomas in the 1980s, expecting to improve tumor control rates. Some reports showed that the total radiation dose could be increased without increasing late radiation damage by using hyperfractionated radiotherapy. We calculated the early and late biologically effective doses (BED) for conventional and hyperfractionated radiotherapy to predict the early and late radiation damage based on the linear-quadratic model (L-Q model). Setting the values of the alpha/beta ratio and t1/2 (half time repair) in the L-Q model is still controversial, and few reports deal with t1/2. Assuming t1/2 = 0.5 hour, the total radiation dose can be up to 71 Gy by hyperfractionated schedule (1.2Gy/fr. 2 times/day) without increasing the late BED of conventional schedule (2Gy/day, total 60Gy). However, the late BED should be increased in tissues with a larger t1/2 value, even if applying the same hyperfractionated schedule. Thus, it is not recommended to apply the same hyperfractionated protocol to all organs.
放射治疗在癌症治疗中的需求日益增加，然而，辐射剂量受到其对正常组织的晚期效应的限制。20世纪80年代，超分割放疗被应用于各类癌症患者，期望提高肿瘤控制率。一些报告表明，通过使用超分割放疗，可以在不增加晚期辐射损伤的情况下增加总辐射剂量。我们基于线性二次模型（L-Q模型）计算了常规放疗和超分割放疗的早期和晚期生物等效剂量（BED），以预测早期和晚期辐射损伤。在L-Q模型中设置α/β比值和t1/2（半修复时间）的值仍存在争议，且很少有报告涉及t1/2。假设t1/2 = 0.5小时，通过超分割方案（1.2Gy/次，每天2次），总辐射剂量可高达71Gy，而不会增加常规方案（2Gy/天，共60Gy）的晚期BED。然而，即使应用相同的超分割方案，t1/2值较大的组织中的晚期BED也会增加。因此，不建议对所有器官应用相同的超分割方案。
