AN ESTIMATE OF TIIE RISK IN PUlDIATION TTiERAPY

The integral dose of accelerator-produced leakage neutrons to patients undergoing high-energy photon therapy is estimated and compared to other sources of integral dose. The leakage neutron component contributes about 5 g rad for a typical treatment course of 5000 rad. When averaged over a 70-kg tissue volume, the corresponding dose amounts to only 0.36 rad. From this, the risk of inducing fatal malignancies by leakage neutrons is estimated to be about 50 x 10 -6 per year following treatment. This is compared to other risks to which the patient is unavoidably exposed, and it is argued that the unwanted neutrons pose such small additional risk that regulatory intervention is not warranted. This assessment is performed without reference to neutron RBE or quality factor. Submitted to Medical Physics * Based in part on presentation for panel discussion at the NBS-BRH Conference on Neutrons from Electron Medical Accelerators, held at the National Bureau of Standards, Gaithersburg, MD, April 9-10, 1979. Work supported by the Department of Energy under Contract Number DE-AC03-76SF00515.