Application of an automated dose accumulation workflow in high-risk prostate cancer - validation and dose-volume analysis between planned and delivered dose

Inter-fraction organ variations cause deviations between planned and delivered doses in patients receiving radiotherapy for prostate cancer. This study compared planned (DP) vs accumulated doses (DA) obtained from daily cone-beam computed tomography (CBCT) scans in high-risk- prostate cancer with pelvic lymph nodes irradiation. An intensity-based deformable image registration algorithm used to estimate contours for DA was validated using geometrical agreement between radiation oncologist's and deformable image registration algorithm propagated contours. Spearman rank correlations (rs) between geometric measures and changes in organ volumes were evaluated for 20 cases. Dose-volume (DV) differences between DA and DP were compared (Wilcoxon rank test, p < 0.05). A novel region-of-interest (ROI) method was developed and mean doses were analyzed. Geometrical measures for the prostate and organ-at-risk contours were within clinically acceptable criteria. Inter-group mean (± SD) CBCT volumes for the rectum were larger compared to planning CT (pCT) (51.1 ± 11.3 cm3vs 46.6 ± 16.1 cm3), and were moderately correlated with variations in pCT volumes, rs = 0.663, p < 0.01. Mean rectum DV for DA was higher at V30-40 Gy and lower at V70-75 Gy, p < 0.05. Mean bladder CBCT volumes were smaller compared to pCT (198.8 ± 55 cm3vs 211.5 ± 89.1 cm3), and was moderately correlated with pCT volumes, rs = 0.789, p < 0.01. Bladder DA was higher at V30-65 Gy and lower at V70-75 Gy (p < 0.05). For the ROI method, rectum and bladder DA were lower at 5 to 10 mm (p < 0.01) as compared to DP, whilst bladder DA was higher than DP at 20 to 50 mm (p < 0.01). Generated DA demonstrated significant differences in organ-at-risk doses as compared to DP. A well-constructed workflow incorporating a ROI DV-extraction method has been validated in terms of efficiency and accuracy designed for seamless integration in the clinic to guide future plan adaptation.