Comparative analysis ofapplication value and setup error between two setup methods in proton and carbon ion therapy for prostate cancer

Abstract

Objective To compare the application values and setup errors between vacuum bag plus body mask and customized alpha cradle duringproton and carbon therapy using Siemens 6D robotic couch in prostate cancer patients. Methods Nineteen patients received vacuum bag plus body mask setup were allocated into the vacuum bag group and19 patients with alpha cradle were assigned into the alpha cradle group. Orthogonal X-ray portals were performed to verify the treatment position before beam delivery in every fraction. The couch correction between the portal and reference DRR through manual image registration was recorded as setup errors in 6 directions including the lateral, supine-inferior, anterior-posterior, yaws, roll and pitch, respectively. Two-tail t-test was used to analyze the setup error data from each direction between two groups. Results In total, 452 and 436 sets of data errors were collected from the vacuum bag and alpha cradle groups. The average setup errors and standard deviation in the vacuum bag and alpha cradle groups in the lateral, supine-inferior, anterior-posterior, yaws, roll and pitch directions were (0.63±0.48) cm vs. (0.33±0.24) cm (P=0.000), (0.40±0.3) cm vs. (0.31±0.25) cm (P=0.000), (0.69±0.61) cm vs. (0.82±0.69) cm (P=0.006), 0.65°±0.47°vs 0.32°±0.25°(P=0.000), 1.05°±0.95°vs 1.16°±0.94°(P=0.100) and 0.67°±0.56°vs 0.40°±0.36°(P=0.000), respectively. The maximum setup errors were detected in the pitch direction for both groups. Conclusions During the proton and carbon therapy using Siemens 6D robotic couch, two setup methods using vacuum bag plus body mask and customized alpha cradle should be selected according to the individual conditions of patients. A customized foot fixer should be utilized to reduce the uncertainty in the femoral head region. Key words: Prostatic neoplasms/proton heavy ion therapy; Radiotherapy planning, computer-assisted; Setup error