Radiation tolerance of the spinal cord.

A series of nine cases of radiation myelopathy seen at the University of California, San Francisco (UCSF) is reviewed, and their treatment data converted into nominal single doses (NSD) and equivalent single doses (ED). The 1% incidence level of myelopathy in the thoracic cord is 1015 rets (ED), and the 50% incidence level is 1476rets (ED). Caution should be used when utilizing a rapid fractionation schedule; it appears that 2000 rads in 5 fractions and 3000 rads in 10 fractions is a safe regimen for the thoracic spinal cord.