308 - Patterns of Nodal Failure after Cervical Cancer Chemoradiotherapy: The Role of Geometric Miss and Baseline Nodal Signal
Presenter(s)
S. Su1, W. Sittiwong2, A. Venkatesan3, T. Prasartseree2, Y. Kim1, S. Eleraky4, J. Wang1, L. L. Lin5, A. Jhingran6, L. Colbert6, C. R. Weil6, M. M. Joyner6, N. Taku6, A. Z. Kesaria6, and A. H. Klopp6; 1Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 2Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand, 3Department of Diagnostic Radiology, The University of Texas MD Anderson Cancer Center, Houston, TX, 4Rice University, Houston, TX, 5Department of Radiation Oncology, MD Anderson Cancer Center, Houston, TX, 6Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s): Despite excellent local control with EBRT plus IGABT for cervical cancer, regional nodal recurrences remain a major cause of failure. EMBRACE II found FDG avidity to be predictive of recurrence but reported a mixed association between baseline nodal volume and subsequent nodal failure. Nonetheless, clinically apparent recurrences still occur in boosted nodes. This study aimed to (1) reassess whether baseline nodal volume and metabolic activity predict recurrence treated with sequential nodal boosting, and (2) characterize spatial patterns of relapse relative to delivered dose and target coverage, including in-field and marginal failures, and evaluate whether subtle baseline imaging abnormalities were under-recognized at initial delineation.
Materials/Methods: Thirty-four patients with locally advanced cervical squamous cell carcinoma treated on the COACH or IMMUNOCERV trial were analyzed (FIGO 2018 IB3–IVA; primary =5 cm and/or imaging-positive pelvic/para-aortic nodes). All nodal targets GTVn (n=190; pathological or macroscopic) received definitive chemoradiotherapy with weekly cisplatin and EBRT with sequential boost to 55-65 Gy EQD2; nodes were recontoured on boost CT. Sequential boost CT was registered to primary planning CT, and the volume of GTVn recontoured on boost CT extending outside the PTVn on the primary planning CT was calculated as a surrogate for geometric miss. Nodal recurrence at any time, including initial site of recurrence or recurrence following distant metastasis was tracked for up to 2 years after treatment on 18F FDG PET/CT. These PET/CT were deformably registered to the planning CT to localize recurrences nodes and assess delivered dose. Logistic regression evaluated associations between recurrence and baseline SUVmax, nodal volume, and dose metrics. For recurrent cases, a senior radiologist blinded to dosimetry performed retrospective side-by-side review of baseline and post-treatment imaging.
Results: Thirty-two nodal recurrences were identified in 9 patients: 10 in boosted nodes, 12 in-field with elective coverage (~45 Gy), and 8 marginal (>0 & <45 Gy). Baseline nodal volume and SUVmax were associated with recurrence (p=0.04 and 0.0003, respectively). In multivariable analysis, volume of boost GTVn outside the PTVn on primary CT independently predicted recurrence (OR 11.0, 95% CI 2.5–47, p=0.001). Retrospective review of all 9 patients with recurrence identified 6 patients with non-pathologically enlarged but with subtle nodal findings on diagnostic images that were not incorporated into target volumes but corresponded with sites of subsequent in field recurrences.
Conclusion: Nodal failure appears driven less by baseline size or FDG avidity and more by geometric miss and anatomic change, supporting adaptive strategies. Under-recognized baseline nodal abnormalities suggest a role for decision-support tools, including automated detection/segmentation, or radiomics, to improve nodal identification at planning.