Clinical impact of setup shift application on image registration for hypofractionated prostate cancer treatment

Abstract

Background: Daily cone-beam computed tomography (CBCT) image-guided registration improves prostate radiotherapy accuracy; however, its dosimetric impact in routine practice, particularly in resource-limited settings, remains under-reported. Aim: To evaluate the effect of daily CBCT image-guided couch shifts on delivered planning target volume (PTV) dose during moderately hypofractionated prostate radiotherapy. Setting: The study was conducted at Steve Biko Academic Hospital in Pretoria, South Africa. Methods: This retrospective study included 30 patients treated for localised prostate cancer between 2019 and 2022 with moderately hypofractionated radiotherapy (60 Gy in 20 fractions) delivered using volumetric arc radiotherapy. Daily CBCT-based soft-tissue registrations were used to derive couch shifts. CBCT datasets were incorporated into the treatment planning systems for dose recalculation using original beam parameters, after transferring anatomical information from CBCT to planning computed tomography (CT) images. Planned versus delivered PTV D98% and D2% were compared using analysis of variance (ANOVA), and regression analysis assessed associations between shift magnitude and dose variation. Results: No significant differences were observed between planned and delivered PTV doses (D98%: p = 0.201; D2%: p = 0.135). Inferior shifts were associated with small reductions in D98%, while superior shifts predicted reductions in D2% (p < 0.05). All variations remained within the clinical threshold. Conclusion: Daily CBCT image-guided couch corrections maintain dosimetric accuracy during hypofractionated prostate radiotherapy and support safe implementation of tight PTV margins in resource-constrained public-sector healthcare settings. Contribution: The findings could be used to determine couch-shift baseline protocols for facilities with limited resources.