Wong C S, Poon J K, Hill R P
Department of Radiation Oncology, Princess Margaret Hospital/Ontario Cancer Institute, Toronto, Canada.
Radiother Oncol. 1993 Feb;26(2):132-8. doi: 10.1016/0167-8140(93)90094-o.
The influence of the level of initial radiation damage on the long term recovery and re-irradiation tolerance in the rat spinal cord was investigated. Rats were irradiated with 0, 10, 20, 30 and 36 daily fractions of 2.15 Gy initially representing 0, 25, 50, 75 and 90% of cord tolerance. After an interval of 20 weeks, retreatments were given using graded single doses of X-ray. The end-point was paralysis of the forelimbs due to white matter necrosis. Latent times to paralysis were inversely proportional to the level of initial injury and retreatment doses. The retreatment ED50S were 19.0, 17.0, 15.7, 14.0 and 11.8 Gy for the control animals and animals irradiated initially with 10, 20, 30 and 36 fractions of 2.15 Gy respectively. Using the extrapolated response dose (ERD) concept, alpha/beta of 3.0 Gy, the retreatment ED50S in % ERD were 81, 70, 58 and 42% after initial doses of 25, 50, 75 and 90% ERD respectively. The level of initial injury appeared to influence the proportion of residual injury. For an initial injury of 25 and 90% of ERD, the respective residual injury was 74 and 65% of the initial damage; for an initial injury of 50 and 75% ERD, the residual injury decreased to 59 and 57% respectively. It is concluded that there was significant long-term recovery in the rat spinal cord, and that the level of initial radiation damage influenced both the retreatment tolerance and the time to expression of injury.
研究了初始辐射损伤水平对大鼠脊髓长期恢复及再照射耐受性的影响。大鼠分别接受0、10、20、30和36次每日剂量为2.15 Gy的照射，初始剂量分别相当于脊髓耐受量的0、25、50、75和90%。间隔20周后，给予分级单次X射线再照射。终点指标为因白质坏死导致的前肢麻痹。麻痹的潜伏时间与初始损伤水平和再照射剂量成反比。对照组动物以及最初分别接受10、20、30和36次2.15 Gy照射的动物，其再照射ED50分别为19.0、17.0、15.7、14.0和11.8 Gy。采用外推反应剂量（ERD）概念，α/β为3.0 Gy，初始剂量分别为25%、50%、75%和90% ERD后，再照射ED50以% ERD计分别为81%、70%、58%和42%。初始损伤水平似乎影响残余损伤的比例。对于初始损伤为25%和90% ERD的情况，相应的残余损伤分别为初始损伤的74%和65%；对于初始损伤为50%和75% ERD的情况，残余损伤分别降至59%和57%。结论是大鼠脊髓存在显著的长期恢复，且初始辐射损伤水平既影响再照射耐受性，也影响损伤表达的时间。
