Retrospective Analysis of CBCT-Based Repositioning During Prostate Radiotherapy

Abstract

Author(s): Anas Ardouz, Abdelouahab Abarane, Youness Khobbaizi, Mustapha Bougteb, Mounir Mkimel, Redouane El Baydaoui

Objective: To retrospectively evaluate the effectiveness of cone-beam computed tomography (CBCT)-based repositioning during prostate radiotherapy and to assess its impact on treatment accuracy and safety margins. Methods: This retrospective study included a cohort of patients with prostate cancer treated with external beam radiotherapy at Casablanca General Hospital. For each treatment session, a CBCT scan was acquired to quantify interfractional setup deviations along the left-right (LR), anterior-posterior (AP), and superiorinferior (SI) axes. Statistical analyses were performed to determine the mean displacements and the probability of exceeding conventional safety margins. Results: Overall, several hundred CBCT scans were analyzed. The mean displacements were 0.31 cm along the LR axis, 0.21 cm along the SI axis, and less than 0.5 cm along the AP axis. The probability of a displacement greater than 3 mm was 41% for the LR axis, compared with 8% for the SI axis and a negligible value for the AP axis. The LR axis was identified as the most critical direction, with displacement amplitudes reaching up to 1.6 cm. The use of CBCT reduced residual setup errors to less than 3 mm in the majority of cases, thereby improving prostate target coverage and enhancing the protection of organs at risk. Conclusion: CBCT is a reliable and effective tool for daily patient repositioning in prostate cancer radiotherapy. Our findings show that the lateral (LR) axis is the most prone to clinically significant displacements, supporting the need for appropriately adapted treatment margins. The systematic integration of CBCT into daily practice improves treatment precision and may reduce the risk of rectal and bladder toxicity, in agreement with findings reported in the international literature.

Share this article