The Physics and Dosimetry of Fast Neutrons for Radiotherapy.

摘要

The practical methods for generating fast-neutron beams for cancer radiotherapy are compared (DT versus D on Be). A general effort is made to compare and contrast the interactions and depth-dose patterns for gamma ray beams with those for the NRL fast-neutron beam of app. 14-MeV average energy (35-MeV D+ on Be). Typical instrumentation for dosimetry and monitoring are described, and the procedure for absolute dose calibration of non-tissue-equivalent ionization chambers is outlined, based on application of the Bragg-Gray relation. The buildup of the dose by the secondary proton field in TE first few millimeters of tissue (which gives rise to 'skin-sparing' in radiotherapy) has been measured in TE plastic, and the compromise of skin sparing by superposition of various materials is also shown, along with restoration of skin sparing by interposing lead foils to filter out the recoil protons. Narrow-broad-beam attenuation coefficients for 60 Co gamma rays vs the NRL neutron beam are shown for a variety of materials, and some semi-broad-beam data for Benelex (pressed wood), Pb, and Fe are also included. (Author)