RADIATION MYELOPATHY FOLLOWING SINGLE COURSES OF RADIOTHERAPY AND RETREATMENT

Purpose: To assess the latent time, survival and dose-fractionation fa ctors associated with permanent radiation myelopathy following single and multiple courses of radiotherapy to the spinal cord. Methods and M aterials: A retrospective analysis was undertaken of all patients who were registered at the Princess Margaret Hospital between 1955 and 198 5, and who developed permanent radiation myelopathy. There were 22 mal es and 13 females with ages ranging from 30 to 72 years. Twenty-four p atients developed permanent myelopathy after one course of radiation t herapy and 11 patients following retreatment. Seven patients had histo logical confirmation of radiation myelopathy at autopsy. Results: The actuarial survival was 14% at 5 years (median: 8.3 months) from the da te of diagnosis of radiation myelopathy. Latent times for myelopathy f ollowing a single course of treatment (mean: 18.5 months, 7-57 months) , were significantly longer than those after reirradiation (mean: 11.4 months, 4-25 months), p = 0.03. There was not a single incident of my elopathy in patients who received fractionated radiotherapy given once daily to an extrapolated response dose (ERD) of I 100 Gy, (equivalent to 50 Gy in 25 daily fractions). Four patients who developed myelopat hy after an ERD of < 100 Gy, were all treated on accelerated fractiona tion protocols with multiple fractions given per day. Patients who wer e reirradiated received significantly higher doses (mean ERD of 148 Gy (2)) than those who had a single course of treatment (mean ERD of 121 Gy(2)), p = 0.001. Conclusion: We conclude that the risk of radiation myelopathy following conventionally fractionated radiotherapy to the s pinal cord is extremely small; giving multiple fractions per day reduc es the spinal cord tolerance; latent time to myelopathy decreases foll owing retreatment; and there is possible long-term recovery of radiati on damage in the human spinal cord.