ESTIMATES OF WHOLE-BODY DOSE-EQUIVALENT PRODUCED BY BEAM INTENSITY-MODULATED CONFORMAL THERAPY

Purpose: To estimate the dose delivered to patients by photons and neu trons outside the radiation fields when beam intensity modulation conf ormal radiotherapy is given, These estimates are then used to compute the risk of secondary cancers as a sequela of the radiation therapy, M aterials and Methods: The x-ray and neutron leakage accompanying two b eam-intensity modulation techniques delivered by currently available l inear accelerators were estimated for 6-MV, 18-MV, and 25-MV x-ray ene rgies, Estimates of whole-body dose equivalents were determined using leakage measurements reported in the literature and treatment paramete rs derived for two modulated beam-intensity conformal therapy techniqu es, Risk values recommended by the National Council on Radiation Prote ction and Measurements(NCRP) were used to estimate the resulting risk of fatal radiation-induced cancer for 70.00 Gy prescribed tumor doses. Results: The computed worst-case risks of secondary cancers increased in the range from 1.00% for 6-MV x-rays to 24.4% for 25-MV x-rays. Co nclusions: Careful consideration should be made of the risks associate d with secondary whole-body radiation before implementation of beam in tensity modulated conformal therapy at x-ray energies greater than 10 MV. (C) 1997 Elsevier Science Inc.