Ruifrok A C, Kleiboer B J, van der Kogel A J
Institute of Radiotherapy, University of Nijmegen, The Netherlands.
Int J Radiat Oncol Biol Phys. 1992;24(3):505-10. doi: 10.1016/0360-3016(92)91066-v.
To investigate the influence of age at irradiation on single dose radiation tolerance and fractionation sensitivity, the cervical spinal cord of rats was irradiated at the age of 1 week and at 15-18 weeks (adult). While the main histological lesions seem to be comparable after irradiation at the two ages, differences were found in single dose tolerance, latency to paresis due to white matter lesions, and fractionation sensitivity. The 50% effect dose (ED50) for single dose irradiation at one week was 19.5 Gy, which is only 10%, but significantly (p < 0.05), lower than the ED50 of about 21.5 Gy at 3 weeks and above. The latency to paresis was clearly influenced by the age at irradiation. The latency in the rats irradiated at 1 week was about 2 weeks, while for adult rats a latency of about 8 months was observed. The fractionation sensitivity for irradiation at 1 week was lower than the fractionation sensitivity of the adult rats; the alpha/beta value at 1 week was estimated to be 4.5 Gy, while for the adult rats an alpha/beta value of 1.8 Gy was found. As a consequence, the observed small difference in tolerance to single doses between 1 week-old and adult rats is further enhanced after fractionated irradiation. During prolonged irradiation treatments this decreased tolerance may be compensated by a higher proliferation rate in the immature central nervous system. The results of the present experiments indicate that, for a single tissue and endpoint, paresis due to white matter lesions in the rat cervical spinal cord, the latency to expression of damage and the fractionation sensitivity clearly change with age at irradiation.
为研究照射时年龄对单剂量辐射耐受性和分次照射敏感性的影响，对1周龄和15 - 18周龄（成年）大鼠的颈脊髓进行照射。虽然两个年龄组照射后主要组织学损伤似乎相当，但在单剂量耐受性、白质损伤导致轻瘫的潜伏期和分次照射敏感性方面发现了差异。1周龄时单剂量照射的50%效应剂量（ED50）为19.5 Gy，仅为3周龄及以上约21.5 Gy的ED50的10%，但差异具有统计学意义（p < 0.05）。轻瘫潜伏期明显受照射时年龄的影响。1周龄照射的大鼠潜伏期约为2周，而成年大鼠观察到的潜伏期约为8个月。1周龄时照射的分次照射敏感性低于成年大鼠；1周龄时的α/β值估计为4.5 Gy，而成年大鼠的α/β值为1.8 Gy。因此，分次照射后，1周龄和成年大鼠之间观察到的单剂量耐受性的微小差异进一步增大。在延长照射治疗期间，这种降低的耐受性可能通过未成熟中枢神经系统较高的增殖率得到补偿。本实验结果表明，对于单一组织和终点，即大鼠颈脊髓白质损伤导致的轻瘫，损伤表达的潜伏期和分次照射敏感性随照射时年龄明显变化。
