Online adaptive radiotherapy of anal cancer: Normal tissue sparing, target propagation methods, and first clinical experience

• Published in: Radiotherapy and oncology Vol. 176; pp. 92 - 98
• Main Authors: Åström, Lina M., Behrens, Claus P., Storm, Katrine Smedegaard, Sibolt, Patrik, Serup-Hansen, Eva
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01.11.2022
• Subjects: Anal cancer; Anus Neoplasms - radiotherapy; Artificial intelligence; Humans; Image-guided radiotherapy; Normal tissue; Online adaptive radiotherapy; Organs at Risk; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Image-Guided - methods; Radiotherapy, Intensity-Modulated - methods; Re-optimization; Retrospective Studies; Online adaptive radiotherapy; Image-guided radiotherapy; Normal tissue; Artificial intelligence; Anal cancer; Re-optimization
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2022.09.015

•Online adaptive radiotherapy (oART) of anal cancer enabled PTV margin reductions.•oART reduced critical dose-volume parameters of bowel bag and bladder.•Rigid propagation was necessary for an efficient and safe oART workflow.•CBCT-guided oART was feasible for patients with anal cancer. Online adaptive radiotherapy (oART) potentially spares OARs as PTV margins are reduced. This study evaluates dosimetric benefits, compared to standard non-adaptive radiotherapy (non-ART), target propagation methods, and first clinical treatments of CBCT-guided oART of anal cancer. Treatment plans with standard non-ART and reduced oART PTV margins were retrospectively generated for 23 consecutive patients with anal cancer. For five patients randomly selected among the 23 patients, weekly CBCT-guided oART sessions were simulated, where the targets were either deformed or rigidly propagated. Preferred target propagation method and dose to OARs were evaluated. Ten consecutive patients with anal cancer were treated with CBCT-guided oART. Target propagation methods and oART procedure time were evaluated. For the retrospective treatment plans, oART resulted in median reductions in bowel bag V45Gy of 11.4 % and bladder V35Gy of 16.1%. Corresponding values for the simulated sessions were 7.5% and 27.1%. In the simulated sessions, 35% of all targets were deformed while 65% were rigidly propagated. Manual editing and rigid propagation were necessary to obtain acceptable target coverage. In the clinical treatments, the primary and some elective targets were rigidly propagated, while other targets were deformed. The median oART procedure time, measured from CBCT acquisition to completion of plan review and QA, was 23 min. Simulated oART reduced the dose to OARs, indicating potential reduction in toxicity. Rigid propagation of targets was necessary to reduce the need for manual edit. Clinical treatments demonstrated that oART of anal cancer is feasible but time-consuming.