Optimizing multiple acquisition planning CT for prostate cancer IMRT

This study evaluated the feasibility of an optimized multiple acquisition planning computed tomography (MPCT) approach, along with daily cone-beam computed tomography (daily CBCT), for intensity-modulated radiotherapy (IMRT) for prostate cancer. We used MPCT to calculate the three-dimensional (3D) displacement error between the pelvic bone and a matching fiducial marker and grouped these error values by whether they were <= 1, 1-2, or >= 3 mm. The 3D displacement errors of MPCT and daily CBCT images were then compared. Correlations between the 3D displacement error values obtained for MPCT and differences between the errors of MPCT were analyzed. Furthermore, the proportions of 3D displacement error values between MPCT and daily CBCT that exceeded 1, 3, and 5 mm were compared among three groups stratified by MPCT 3D displacement error values of <= 1, 1-2, or >= 3 mm. In a correlation analysis of the 3D displacement error values of MPCT and daily CBCT, a significant difference was observed when MPCT groups with 3D displacement errors >= 3 mm were compared (p < 0.0001). The proportions of 3D displacement errors between MPCT and daily CBCT >= 3 mm were 13.5%, 27.6%, and 74.5% for the < 1 mm, 1-2 mm, and >= 3 mm groups, respectively. Systematic errors during treatment can be attributed to the relationship between the pelvic bone and random shifts in the prostate between each planning MPCT(> 3 mm) image. To avoid these errors, optimal planning CTcan be estimated by selecting CT images with the smallest 3D displacement error.