USE OF PORTAL RADIOGRAPHY TO INCREASE ACCURACY OF DOSE DELIVERY IN RADIATION-THERAPY

Port films were acquired for all radiation therapy patients (n = 132) treated over a thirteen month period to 1] assist in initial treatment field set-up on Day 1, 2] for quality assurance with a second port fi lm taken on Day 7 of radiation therapy, and 3] as a means to document the radiation treatment field as a part of the patients permanent medi cal record. Port films were used for both patients treated with a defi nitive course of radiation (n = 97 patients), and those treated pallia tively (n = 35 patients). The portal radiographs were valuable in term s of the initial set-up, and to correct for any positioning or other e rrors at the time of the one week recheck. Changes were made, based on the initial port film on Day 1, in 53% and 57% of treatment fields fo r palliative and definitive radiation patients, respectively. The chan ges made in both definitively and palliatively irradiated patients wer e usually in field position, an increase in field size to include all of the tumor, or a decrease in field size to spare normal tissue. Fewe r changes were necessary based on the Day 7 recheck port films, but th ese day-7 rechecks are recommended for quality control. Based on the h igh frequency of changes introduced because of the initial port film f indings, it is recommended that port films be incorporated on a routin e basis in veterinary radiation therapy.