A prospective comparison of three systems of patient immobilization for prostate radiotherapy.
OBJECTIVE
The study compared the setup reliability of 3 patient immobilization systems, a rubber leg cushion, the alpha cradle, and the thermoplastic Hipfix device, in 77 patients with cT1-T3, N0, M0 prostate cancer receiving conformal radiotherapy.


METHODS
Port films were analyzed and compared to simulation films to estimate the setup errors in the three coordinate axes (anterior-posterior, cranial-caudal, medial-lateral). A total vector error was calculated from these shifts.


RESULTS
The Hipfix was found significantly superior to the other two devices 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 axes, whereas the deviation for the other two systems ranged from 2.7 to 3. 4 mm. Errors greater than 10 mm were virtually eliminated with the Hipfix system. There was a reduction in the mean total vector error in the alpha cradle and Hipfix patient cohorts over time, reflecting improved efficacy as a result of experience.


CONCLUSIONS
There was a significant difference in the performance of each immobilization device. The Hipfix was consistently more reliable in reducing setup errors than the other devices.
Malone
S
S
Ottawa Regional Cancer Centre, General Division, Ottawa, Ontario, Canada. smalone@cancercare.on.ca
Szanto
J
J
Perry
G
G
Gerig
L
L
Manion
S
S
Dahrouge
S
S
Crook
J
J
D000704:Analysis of Variance; D006801:Humans; D007103:Immobilization; D008297:Male; D009367:Neoplasm Staging; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000295:instrumentation / Q000379:methods*; D015203:Reproducibility of Results