Offline adaptive radiotherapy for hypofractionated prostate therapy

The study was conducted retrospectively at the Radiation Oncology, Steve Biko Academic Hospital. Data from 30 patients who underwent localised prostate cancer treatment were analysed, with a primary focus on the CBCT images obtained after applying treatment couch shifts to verify the treatment setup. These CBCT images were used to create new plans, which were then compared to reference plans based on the initial CT images. The 3-dimensional couch shift coordinates were evaluated against different absorbed dose constraints on the Planning Target Volume (PTV), specifically D2% (maximum absorbed dose) and D99%≥57 Gy (minimum absorbed dose). After applying couch shifts, the average results showed no significant difference between the planned and treated absorbed doses for D98% (F = 1.570, p = 0.201 > 0.05) and D2% (F = 1.841, p = 0.135 > 0.05). However, linear regression analysis revealed that inferior couch shifts significantly predicted D98% during treatment, while superior (SUP) couch shifts significantly predicted D2% during treatment. Notably, each unit of superior couch shift led to a 1.797 Gy decrease in D2% during treatment (t = -3.036, p < 0.05), with a negative beta value (β = -1.797). Despite these findings, the overall dose to the PTV did not significantly differ from the planning objectives. The differences in mean shifts and dosimetric plans/re-plans were compared using the ANOVA analysis.