ESTRO 2025 - Abstract Book

S1195

Clinical – Lower GI

ESTRO 2025

2215

Digital Poster Dosimetric and clinical impact of bone marrow-sparing radiotherapy for anal cancer: A systematic review Jasmine Chen 1 , Elizabeth Forde 2,3 , Shao Hui Huang 1,4 , Michelle Leech 2,3 , Ali Hosni 1,4 , Rouhi Fazelzad 5 , Amy Liu 6 , John Kim 1,4 1 Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada. 2 Applied Radiation Therapy Trinity, Discipline of Radiation Therapy, Trinity College Dublin, Dublin, Ireland. 3 Radiation Oncology, Trinity St James’s Cancer Institute, Dublin, Ireland. 4 Department of Radiation Oncology, University of Toronto, Toronto, Canada. 5 Library and Information Services, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada. 6 Department of Biostatistics, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada Purpose/Objective: Concurrent chemoradiation with organ preservation is the standard of care for patients with anal squamous cell carcinoma. An important treatment-related toxicity is myelosuppression, which may lead to chronic infection, and treatment interruption. Treatment-related lymphopenia has been suggested as associated with poor overall survival in anal cancer. Bone marrow (BM)-sparing IMRT has the potential to minimize radiation dose to pelvic BM, thereby reducing the risk of treatment-related toxicity. The purpose of this systematic review was to investigate dosimetric feasibility and clinical benefits of BM-sparing IMRT planning in anal cancer. Material/Methods: This systematic review was registered in PROSPERO (CRD42024427240). Five bibliographic databases were searched from inception to July 2024 to identify studies investigating BM-sparing IMRT techniques and clinical benefits. Eligible studies were screened by two independent reviewers following JBI guidelines and reported based on PRIMSA 2020. The quality of selected studies were appraised using JBI tools. Imaging selection, structural definition, planning constraints of IMRT-relevant BM, and dose reduction in BM-sparing planning were analyzed. Response measurement tools, confounding factors, and evidence of acute and late hematologic toxicity (HT) were evaluated as clinical benefits. Descriptive statistics were used. Results: Thirty-two studies were included. The outer table of the whole pelvic bone was the most frequently used surrogate for BM, followed by ilium, lumbar-sacrum, and lower pelvis. Contouring variation of lumbar sacrum was observed in 15 studies. The differences were primarily located at L4 vertebrae, and the inferior portion of sacrum and coccyx. Ten studies used FDG-PET to define active bone marrow (ABM) and four types of standardized uptake value (SUV) normalization strategies were proposed. Dosimetric findings demonstrated that BM/ABM constraints could lead to reduced BM dose by 0-47%. The greatest reduction was seen in proton therapy. Overall, clinically derived predictors addressed the importance of limiting low-to-intermediate dose sparing to the whole pelvis and lumbar-sacrum. Variation in assessment tools and study endpoints were incorporated in the dosimetric-response modeling (Table 1). A wide range of HT was observed and compared in patients treated with and without BM-sparing IMRT.