Re-irradiation of the human spinal cord

Experimental animal data give evidence of long-term recovery of the spinal cord after irradiation. By extrapolation of these data, re-irradiation regimens were designed for eight patients who required palliative radiotherapy. As a consequence of re-irradiation, their spinal cords were exposed to cumulative doses exceeding the tolerance dose. Radiobiological and clinical data are presented. Eight patients were re-irradiated on the cervical (n = 1), thoracic (n = 5) and lumbar (n = 2) spinal cord. The time interval between the initial and re-treatment ranged from 4 months to 12.7 years (median: 2.5 years). (Re-)treatment schemes were designed and analyzed on basis of the biologically effective dose (BED) according to the linear-quadratic model. The repair capacity (alpha/beta ratio) for the cervico-thoracic and lumbar spinal cord was assumed to be 2 Gy and 4 Gy, with a BEDtolerance of 100 Gy and 84 Gy, respectively. The cumulative irradiation dose applied to the spinal cord varied between 125 and 172% of the BEDtolerance. During follow-up, ranging from 33 days to > 4.5 years (median: 370 days) none of the patients developed neurological complications. Seven patients died from tumor progression, and one patient is still alive. Long-term recovery of the spinal cord from radiation injury, which has been demonstrated in rodents and primates, may also occur in humans