2871 - Exploratory Study on the Correlation between Pelvic Bone Marrow Dose-Volume Effects and Changes in Peripheral Blood Lymphocyte Subpopulations after Whole Pelvic Irradiation

10:45am - 12:00pm PT

Hall F

Screen: 7

Presenter(s)

Yi-Wei Wang, - Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiaotong University, School of Medicine, Shanghai, Shanghai

Y. W. Wang¹, M. Chen², and H. P. Xu³; ¹Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiaotong University, School of Medicine, Shanghai, Shanghai, China, ²Rui Jin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, Shanghai, China, ³Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China

Purpose/Objective(s): This study aims to identify optimal dose-volume constraints for pelvic bone marrow and explore their correlation with changes in peripheral blood lymphocyte subpopulations during whole pelvic radiotherapy. Specifically, we seek to determine dosimetric predictive factors for lymphocyte decline and investigate their potential impact on the prognosis of patients with cervical cancer or endometrial cancer.

Materials/Methods: We retrospectively analyzed the clinical data and radiotherapy dosimetric parameters of 50 patients who underwent whole pelvic irradiation. Pelvic bone (B) and bone marrow (BM) were contoured to include the ilium, lumbosacral spine, lower pelvis, and entire pelvis. Dose-volume histograms (DVHs) were generated to calculate V5, V10, V15, V20, V25, V30, V35, V40, V45, and V50 for both pelvic bone and bone marrow. Hematologic toxicity (HT) was graded using the Common Terminology Criteria for Adverse Events (CTCAE - Version 5.0), and changes in lymphocyte subpopulations were assessed as percentage deviations from baseline. Logistic regression analysis was used to evaluate the associations between HT, changes in lymphocyte subpopulations, and DVH parameters.

Results: V15Gy for the pelvic bone > 95% was positively correlated with Grade 2/3/4 anemia (OR = 5.556, P=0.001) and thrombocytopenia (OR=5.632, P=0.007). No significant relationship was observed between bone or bone marrow dose-volume parameters and neutropenia. V15Gy for the pelvic bone > 95% also showed a borderline positive correlation with neutropenia (OR=3.556, P=0.083). For lymphocytes, V40Gy for the lower pelvic bone > 30% was significantly associated with an 80% reduction in CD4 lymphocyte counts during radiotherapy (OR=18.667, P=0.021). No correlation was found between dose-volume parameters and CD3 or CD8 lymphocytes. Investigating lymphocyte recovery at three months post-radiotherapy, V15Gy for the pelvic bone > 95% was negatively correlated with lymphocyte recovery (OR=0.164, P=0.027). A similar trend was seen for CD4 lymphocyte recovery (OR=0.125, P=0.090), while no significant association was found for CD3 or CD8 lymphocyte recovery, likely due to the small sample size. Additionally, no association was observed between immunotherapy and lymphocyte reduction or recovery.

Conclusion: Limiting the dose to pelvic bone (e.g., V15Gy< 95%) significantly reduced hematologic toxicity and may be associated with improved lymphocyte recovery post-radiotherapy, potentially enhancing immunotherapy efficacy. Restricting V40Gy for the lower pelvic bone to < 30% most effectively spared peripheral blood lymphocyte subpopulations. Future studies with larger sample sizes and longer follow-up are needed to validate the clinical application of these strategies.