Room: Exhibit Hall
Purpose: To determine the spatial deviation of different bladder volume for prostate cancer patients with PLN. The purpose of this study is to quantify the interfraction spatial consistency of bladder wall in prostate cancer with bladder scanner.
Methods: A total of 23 prostate patients (bladder volume range in 150 - 500 cc) were enrolled in this study. Bladder scanner volume was recorded before every CBCT. The threshold of percentage differences between CBCT and simulation CT was 10%. 8 CBCTs were obtained for every patient during each treatment. A rigid registration for each of the cone beam CT was performed to the pelvic bones, using bony landmarks to the original planning CT. Bladder during the treatment was contoured in each CBCT scan. Interfraction spatial variation of bladder was evaluated by ratio of bladder volume (RBV, CBCT/CT), Hausdorff distance (HD) and dice coefficient.
Results: 11 patients (88 CBCTs) have been analyzed to date. The average translational shift with bony match was 0.78 Â± 1.0, 2.1 Â± 1.4, 1.4 Â± 1.0 mm for vertical, longitudinal, lateral shifts, respectively. RBV decreased from 17.6% to 10.3% with bladder volume increased. Mean Hausdorff Distance (MHD) of bladder decreased from 0.63 cm to 0.32 cm with bladder volume increased. Dice coefficient increased from 0.73 to 0.89.
Conclusion: In our preliminary study, we focused on the spatial deviation of the bladder wall for different bladder volume. The spatial variation of bladder wall was larger than couch shift. Compared with small bladder volume, patients with larger bladder volume achieved better spatial consistency with higher RBV, Dice coefficient and lower MHD. Significant interfractional variations occur in bladder size and position during prostate RT. Large bladder volume and consistent bladder filling should be taken into account and standard routine for pelvic patients to ensure accurate daily RT delivery.