Guidelines for Complications of Cancer Treatment Vol VIII Part B

Dose Incidence Comments Author>30 Gy 0.18% in 1112 Head & Marcuss andNeck Patients Millon 2045 to 50 Gy 0.42 %56 to 65 Gy 0.7% Only 1 in 144 Patients McCuniffHead & Neck Patients and Liang 21treated by parallelopposed bilateralbeams.The present dose response estimates are:DoseProbable Incidence ofDelayed RadiationMyelopathy45 Gy in 1.8 to 2 Gy/# < 0.2%50 Gy in 1.8 to 2 Gy/# < 1% 1257 – 67 Gy in 1.8 to 2 Gy/# 5% 12,2168 – 73 Gy in 1.8 to 2 Gy/# 50% 17,22Dose per fraction relationship: Dosed higher than conventionaldoses may be associated with higher incidence, howeverexperimental and clinical studies have not shown benefit ofreducing dose per fraction. 23Dose length (volume) relationship: The evidence is conflicting.While some studies show that incidence increases 24,25 withthe length irradiated, many do not. 25,26Segment of Cord: Although assumed classically that dorsalcord has lower tolerance than cervical, this holds true no more.All segments are supposed to carry equal risk.Reirradiation: In most of the animal experiments includingprimates, much of the recovery takes place within 2 years,thus reirradiation if required can be done if 2 years have elapsed333