3747 - Pelvic Bone Marrow Dosimetry and Peripheral T-Cell Subset Dynamics After Cervical Cancer Radiotherapy
Presenter(s)
W. He1,2, Y. Wang1,2, M. Chen1,2, J. Chen1,2, and H. Xu1,2; 1Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China, 2Shanghai Key Laboratory of Proton-therapy, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
Purpose/Objective(s): Radiation-induced lymphopenia is common after pelvic radiotherapy and is associated with inferior outcomes in cervical cancer. While pelvic bone marrow irradiation is recognized as a contributor, the relative importance of specific marrow subregions and dose ranges for long-term T-cell recovery remains unclear. We hypothesized that dose–volume exposure of distinct pelvic bone marrow compartments is differentially associated with sustained peripheral T-cell subset suppression following radiotherapy.
Materials/Methods: Peripheral blood T-cell subsets were prospectively assessed at baseline and at 6 and 12 months after pelvic radiotherapy. Pelvic bone marrow was anatomically segmented into lumbosacral, iliac, and lower pelvic subregions. For each subregion, dose–volume histogram parameters including mean dose and V15–V50 were extracted. Associations between dosimetric parameters and longitudinal changes in T-cell subsets were evaluated using Pearson correlation with false discovery rate adjustment, univariate linear regression, and elastic-net regression with stability selection. Multivariable linear regression was used to assess associations between candidate marrow dose metrics and 6-month CD4? T-cell counts, adjusting for baseline immune status.
Results: Across the cohort, peripheral CD3?, CD4?, and CD8? T-cell populations showed significant post-treatment reductions, with recovery remaining incomplete one year after radiotherapy. Among pelvic marrow compartments, lumbosacral bone marrow dose demonstrated the strongest and most consistent associations with impaired T-cell recovery. Low-to-intermediate dose exposure of the lumbosacral marrow (V15–V30) correlated negatively with multiple T-cell subsets, whereas higher-dose metrics and non-lumbosacral regions showed weaker or inconsistent relationships. Stability selection identified lumbosacral V15–V30 as the most reproducible predictors of sustained T-cell suppression across models. Among these parameters, lumbosacral V30 showed sufficient inter-patient variability and was independently associated with reduced 6-month CD4? T-cell counts after adjustment for baseline values.
Conclusion: Low-to-intermediate dose irradiation of the lumbosacral bone marrow is a key determinant of prolonged peripheral T-cell suppression after pelvic radiotherapy for cervical cancer. Lumbosacral V30 represents a clinically tractable dosimetric parameter within an immune-relevant dose range and may serve as a target for immune-conscious treatment planning. These findings support regional marrow–sparing strategies to mitigate long-term immune toxicity and inform future prospective validation.