An evaluation of the recommendations of the TG-25 protocol for determination of depth dose curves for electron beams using ionization chambers.

AAPM Radiation Therapy Committee Task Group 25 has recently outlined a protocol for the determination of relative dose curves for electron beams [Med. Phys. 18, 73-109 (1991)]. We have performed an evaluation of this protocol by comparing the central axis depth dose curves determined from measurements using two different ionization chambers and three different phantom materials. Measurements were made with a Farmer-type PTW and Capintec ionization chamber in solid water, PMMA, and clear polystyrene phantoms irradiated by 6- and 15-MeV electron beams. Central axis depth dose curves were generated from the measured depth-ionization data using the new protocol. For both the chambers and energies investigated in this study, excellent agreement was observed among all the depth doses in water obtained from measurements in all of the three phantoms studied.