[Radiation tolerance of the human spinal cord]

Chronic myelopathy is among the most serious sequelae of high dose radiation treatment. Therefore medical and forensic reasons warrant detailed knowledge of the radiation tolerance of the human spinal cord.

This paper reviews published data on the incidence of radiation myelopathy in patients treated with megavoltage radiation.

Two years after completion of radiation treatment with daily fractions of approximately 2 Gy development of radiation myelopathy is expected in 1% of the patients at 50 to 55 Gy. An incidence of 5% is estimated to occur at approximately 55 to 60 Gy. At higher doses the risk of spinal cord damage increases steeply. Interpretation of these data has to consider that the incidence of radiation myelopathy increases with increasing time of follow-up. Even after two years no clearcut plateau is observed. High doses per fraction are poorly tolerated by the spinal cord, the alpha/beta-ratio appears to be approximately 1 Gy. Accelerated schedules with < or = 2 Gy per fraction but daily doses greatly exceeding 2 Gy may result in a higher risk of radiation myelopathy than conventionally fractionated treatments. This observation seems, at least in part, to be due to a slow component of repair of sublethal radiation damage in the spinal cord.