Abstract Background The precise application of stereotactic body radiation therapy (SBRT) for prostate cancer is challenged by prostate motion and anatomical variations in surrounding organs such as the bladder and rectum. Online adaptive radiotherapy (oART) using cone beam computed tomography (CBCT) has been shown to improve target coverage while limiting doses to organs-at-risk (OARs). Methods We retrospectively analyzed data from 30 prostate cancer patients who were treated with CBCT-based oART simultaneous integrated boost SBRT in five fractions, divided into two dose groups: lower dose group (LDG) receiving 30 Gy to seminal vesicles and prostate, and 35 Gy to prostate, and higher dose group (HDG) receiving 30 Gy to the vesicles and prostate, and 37.5 Gy boost to the prostate. Target volumes and OARs were contoured and evaluated per fraction. For each fraction, SCH (Scheduled plan) and ADP (Adaptive plan) plans were generated. Eight target volumes and fifteen OAR DVH (Dose Volume Histogram) parameters were collected and analyzed. Statistical comparisons were performed between differences in target coverages and doses to OARs in SCH and ADP plans, and between the LDG and HDG groups. Results Target coverages were significantly improved in ADP plans in both cohorts and across the entire cohort ( p < 0.001). SCH plans often failed to achieve the goal for PTV prostate. The median differences between target volume parameters of SCH and ADP plans were consistent, the adaptive plans were always superior regardless of the prescribed dose. Significant deterioration in ADP was found across the entire cohort in 7 OAR volumes. Dose reductions in OARs due to adaptation were less consistent. Significant differences were observed in bladder, rectum, sigmoid, femur, and penile bulb parameters in the sub-group analysis. The LDG-ADP plans resulted in slightly higher values of rectum D0.04cm3 and rectum D50% than LDG-SCH, whereas in the HDG-ADP plans significantly lower doses for the rectum D0.04cm3 , rectum D1cm3 , bladder wall V18.3 Gy , bladder D40% and higher value for bladder V37Gy , bladder wall D15cm3 , penile bulb D5 cm3 , penile bulb D3cm3 , penile bulb D5cm3 , sigmoid colon D20cm3 were achieved compared to the HDG-SCH plans. The magnitude of target coverage improvement was similar in the LDG and HDG groups, although higher prescribed doses were related to increased OAR doses in both SCH and ADP plans, particularly in the HDG group. Conclusions CBCT-based online adaptive SBRT for prostate cancer significantly improves target coverage compared to the scheduled plans. Although the benefits of OARs dose vary, adaptive planning offers significant dosimetric advantages, especially at higher prescribed doses. These findings support the integration of oART into prostate SBRT to optimize the treatment’s efficacy and safety.
Gáldi et al. (Tue,) studied this question.