Early breast cancer irradiation after conservative surgery: quality control by portal localization films

A review of geometrical errors on portal localization films in 20 patients undergoing breast irradiation after conservative surgery is presented. Patients were immobilized using a cellulose acetate individual cast. Good precision in daily set-up has been noted with a mean ventrodorsal shift of 2.7 mm on medial films and 3.0 mm on lateral films; a mean craniocaudal shift of 1.8 mm on medial films and of 2.0 mm on lateral films have been also observed. The mean half-beam block rotation error has been minimal, ranging 0.8 degrees on medial and 1.1 degrees on lateral films. A new cast was made in 3/20 (15%) patients depending on variation of breast morphology during treatment and on geometrical errors noted by portal localization film check.