The role of cone beam CT in personalization of bladder cancer radiotherapy

This study aimed to evaluate discrepancies between planned, delivered and adapted doses to target and organs at risk (OARs) during bladder cancer radiotherapy, using deformable image registration from CT to CBCT in view of better treatment personalization. Twenty patients with a total of 165 CBCT images were analysed. Intensity modulated techniques (IMRT and VMAT) were simulated in the Monaco planning system. The initial plans were adapted to each CBCT using the Adapt to shape (ATS) function. A reduction in PTV66 and CTV66 coverage was observed upon calculation of treatment dose on CBCTcalc in comparison with plans on CT. The PTV66 coverage was 86.7% IMRT and 86.4% VMAT, respectively. Meanwhile, the optimized plans on CBCTopt provided PTV66 coverage of 97.1% IMRT and 96.4% VMAT, which was similar to the initial planning on CT (97.4% IMRT and 96.6% VMAT). Furthermore, CTV66 showed a coverage of 94.2% IMRT and 94.0% VMAT on CBCTcalc, in comparison to the values on CT (99.8% IMRT and 99.9% VMAT) and the values on CBCTopt (99.8% IMRT and 99.8% VMAT). For OARs, the rectum, bowel bag, and sigmoid exhibited higher values on CBCTcalc than on CT planning and CBCTopt. This study demonstrates that CBCT- guided adaptive radiotherapy enhances treatment precision and personalization in bladder cancer, improving target coverage and reducing radiation exposure to healthy tissues. Next to highlighting the importance of personalizing bladder cancer radiotherapy, the study substantiates that daily reoptimization with ATS constitutes an efficacious strategy in centers with limited resources.