Terry N H, Denekamp J
Br J Radiol. 1984 Jul;57(679):617-29. doi: 10.1259/0007-1285-57-679-617.
Early and late colo-rectal damage in mice have been assessed after 137Cs gamma irradiation and 3 MeV neutrons given as 1,2,5 or 10 fractions. Damage was measured by early changes in body weight, the late production of short faecal pellets and the pattern of lethality after irradiation. The data have been analysed in terms of the time course of expression of damage, fractionation effects and the RBE for neutrons over a wide range of doses per fraction (0.5-12.5 Gy neutrons, 3.5-33.5 Gy gamma rays). An initial epithelial denudation led to an early loss of weight, maximal at 11-17 days after irradiation. A dose-dependent weight reduction persisted over the animals' life-time. Deaths after localised pelvic gamma irradiation were progressive with no sharp demarcation between early or late phases of injury. The time course for lethality was qualitatively similar after neutrons. Beyond six months the rectum became constricted by fibrosis and a higher proportion of small faecal pellets was observed. At 6-15 months relatively shallow dose-response curves were obtained for this change. The sparing effect of fractionation was marked for the gamma-irradiated mice and almost absent after neutrons. A very high repair increment (11 Gy) was seen with two gamma-ray fractions of 20 Gy. At lower doses per fraction the proportion of each gamma-ray fraction recovered was 50-69% for all assays, i.e., similar to that for other normal tissues. There was a slight enhancement in the sparing effect for the late compared with the early assays over the lower dose range. The RBE was strongly dependent on dose per fraction because of the lack of reparable damage after neutrons. The RBE for both early and late effects was 5.0 at a neutron dose per fraction of 1 Gy. Extrapolation of the RBE data to lower doses, using the linear quadratic model, predicts a higher RBE for late (7.4-12.7) than for early damage (5.7-8.5) if gamma-ray doses below 5 Gy are used.
在给予小鼠137Csγ射线和3 MeV中子（以1、2、5或10次分割照射）后，评估了其早期和晚期的结直肠损伤。通过体重的早期变化、短粪便颗粒的晚期产生以及照射后的致死模式来测量损伤。已根据损伤表达的时间进程、分割效应以及在广泛的每次分割剂量范围（0.5 - 12.5 Gy中子，3.5 - 33.5 Gyγ射线）内中子的相对生物效应（RBE）对数据进行了分析。最初的上皮剥脱导致早期体重减轻，在照射后11 - 17天达到最大值。剂量依赖性体重减轻在动物的整个生命周期中持续存在。局部盆腔γ射线照射后的死亡是渐进性的，损伤的早期或晚期之间没有明显的界限。中子照射后致死的时间进程在定性上相似。六个月后，直肠因纤维化而变窄，观察到较高比例的小粪便颗粒。在6 - 15个月时，针对这种变化获得了相对较浅的剂量反应曲线。分割照射对γ射线照射的小鼠具有显著的保护作用，而中子照射后几乎没有。对于20 Gy的两次γ射线分割照射，观察到非常高的修复增量（11 Gy）。在较低的每次分割剂量下，所有检测中每个γ射线分割的恢复比例为50 - 69%，即与其他正常组织相似。在较低剂量范围内，与早期检测相比，晚期检测的保护作用略有增强。由于中子照射后缺乏可修复的损伤，RBE强烈依赖于每次分割剂量。在每次分割中子剂量为1 Gy时，早期和晚期效应的RBE均为5.0。如果使用低于5 Gy的γ射线剂量，使用线性二次模型将RBE数据外推至较低剂量时，预测晚期损伤的RBE（7.4 - 12.7）高于早期损伤（5.7 - 8.5）。
