Positioning of port films for radiation: variability is present.

Purpose: Pelvic radiation treatment demands precision and consistency in patient setup for efficacy of therapy and to limit radiation dosage to normal tissue. Despite the use of immobilization devices and positioning techniques, there is still concern for variation in daily setup. The purpose of this retrospective study was to determine the presence and degree of variation in sacral slope in 20 subjects receiving radiation therapy for pelvic malignancies.