A prospective comparison of three systems of patient immobilization for prostate radiotherapy

Purpose: The study compared the setup reliability of 3 patient immobilizati on systems, a rubber leg cushion, the alpha cradle, and the thermoplastic H ipfix device, in 77 patients with cT1-T3, NO, MO prostate cancer receiving conformal radiotherapy. Methods and Materials: Port films were analyzed and compared to simulation films to estimate the setup errors in the three coordinate axes (anterior-p osterior, cranial-caudal, medial-lateral). A total vector error was calcula ted from these shifts. Results: The Hipfix was found significantly superior to the other two devic es in reducing mean setup errors in all axes (p < 0.005). The average field -positioning error with the Hipfix ranged from 1.9 mm to 2.6 mm for all axe s, whereas the deviation for the other two systems ranged from 2.7 to 3.4 m m. Errors greater than 10 mm were virtually eliminated with the Hipfix syst em. There was a reduction in the mean total vector error in the alpha cradl e and Hipfix patient cohorts over time, reflecting improved efficacy as a r esult of experience. Conclusion: There was a significant difference in the performance of each i mmobilization device. The Hipfix was consistently more reliable in reducing setup errors than the other devices. (C) 2000 Elsevier Science Inc.