The incidence of myelitis after irradiation of the cervical spinal cord.

To further define the tolerance of the cervical spinal cord, the dose of radiation to the cervical spinal cord was calculated for all 2901 patients with malignancies of the upper respiratory tract treated at the University of Florida between October 1964 and December 1987. To further define the population evaluated, certain criteria were used: (a) a minimum of 3000 cGy to at least 2 cm of cervical spinal cord and (b) a minimum of 1 year of follow-up, unless a neurological complication occurred before 1 year. A total of 1112 patients were evaluable, of which 2 (0.18%) developed radiation myelitis. One received 4658 cGy to the cervical cord at 172.5 cGy per day, and the other patient received 4907 cGy to the cord at 169.2 cGy per day. The risk of myelitis at each dose level was 0/124 at 3000-3999 cGy, 0/442 at 4000-4499 cGy, 2/471 at 4500-4999 cGy, and 0/75 at a cord dose of 5000 cGy or greater.