Effectiveness of couch height–based patient set-up and an off-line correction protocol in prostate cancer radiotherapy

Abstract

Purpose: To investigate set-up improvement caused by applying a couch height–based patient set-up method in combination with a technologist-driven off-line correction protocol in nonimmobilized radiotherapy of prostate patients. Methods and Materials: A three-dimensional shrinking action level correction protocol is applied in two consecutive patient cohorts with different set-up methods: the traditional “laser set-up” group ( n = 43) and the “couch height set-up” group ( n = 112). For all directions, left-right, ventro-dorsal, and cranio-caudal, random and systematic set-up deviations were measured. Results: The couch height set-up method improves the patient positioning compared to the laser set-up method. Without application of the correction protocol, both systematic and random errors reduced to 2.2–2.4 mm (1 SD) and 1.7–2.2 mm (1 SD), respectively. By using the correction protocol, systematic errors reduced further to 1.3–1.6 mm (1 SD). One-dimensional deviations were within 5 mm for >90% of the measured fractions. The required number of corrections per patient in the off-line correction protocol was reduced significantly during the course of treatment from 1.1 to 0.6 by the couch height set-up method. The treatment time was not prolonged by application of the correction protocol. Conclusions: The couch height set-up method improves the set-up significantly, especially in the ventro-dorsal direction. Combination of this set-up method with an off-line correction strategy, executed by technologists, reduces the number of set-up corrections required.