Target registration errors with surface imaging system in conformal radiotherapy for prostate cancer: study on 19 patients.

PURPOSE: Accurate patient setup is a prerequisite for conformal radiotherapy (3D-CRT) and is based on various methods, including surface imaging systems. To evaluate the validity of a surface imaging system (AlignRT), we analysed setup reproducibility of a cohort of patients. MATERIALS AND METHODS: Nineteen patients affected by prostate adenocarcinoma were enrolled in this study. We acquired 653 surface images and 99 digital portal images (DPI). Setup errors were found by matching surface images with computed tomography (CT) and DPI images. RESULTS: The setup errors from the threshold of 5 mm detected by AlignRT along the Y, Z and X axes occurred in 47.4%, 42.1% and 5.3% of patients, respectively. For the threshold of 3 mm, shifts along the Y, Z and X axes were observed in 68%, 69% and 10%, respectively. Comparing AlignRT and DPI, we found a statistically significant difference in the detection of shifts along the Y and Z axes. For a threshold ≥5 mm, the two systems provided corresponding setup errors along the Y and Z axes, whereas along the X axis, the threshold was not necessary. CONCLUSIONS: AlignRT is an accurate technique for setup in 3D-CRT prostate cancer patients, especially along the lateral direction.