Radiation Sub-Segmentectomy in 90y Radioembolization: Post-Therapy Dosimetry, Treatment Response, and Pathological Necrosis 📝

Author: Guilherme Rosa Ferreira, Dan Giardina, John Karageorgiou, Chris Malone, Allan Thomas 👨‍🔬

Affiliation: Washington University School of Medicine, Mallinckrodt Institute of Radiology, Washington University School of Medicine 🌍

Abstract:

Purpose: Radiation segmentectomy has become a primary strategy in 90Y radioembolization, with localized treated volumes that can include up to two liver segments. The goal is complete pathological necrosis (CPN) via high mean dose (≥400 Gy) to treated volumes. Here, a modified strategy is explored where treated volumes are smaller than a full liver segment: radiation sub-segmentectomy.
Methods: A total of 27 HCC tumors from 26 glass 90Y cases were segmented from diagnostic MRI while perfused volumes (PV) were segmented from contrast-enhanced cone-beam CT (CBCT) performed during the planning procedure. Tumor and PV contours were registered and transferred to 90Y-SPECT/CT to perform absorbed dose estimates. Post-therapy, voxelized dosimetry was computed from 90Y-SPECT/CT imaging using the local deposition method and activity normalization to the PV. Imaging (mRECIST) and pathological response (liver explant) were tracked for available cases. Treatment parameters and volume and dose metrics for PVs and tumors were compared with response.
Results: Median (range) for PV volume, tumor volume, and tumor size were 47.6 (24.5–206) mL, 7.3 (1.4–51.7) mL, and 2.4 (1.4–4.6) cm, respectively. Mean PV and tumor doses had medians of 854 (304–2232) Gy and 1269 (463–3686) Gy, respectively. All tumors showed objective imaging response: 21 complete-response (CR) and 6 partial-response (PR). Ten of 12 tumors with pathology data showed ≥85% necrosis (all CR). Treatment parameters and volumes showed no significant distinctions between CR and PR (p≥0.07). The % tumor volume receiving ≥400 Gy (V400) aligned strongly with response – all 19 tumors with V400≥95% showed CR while 6/8 with V400<95% had PR. Response in tumors with V400<95% was dictated by V200: <100% aligned with PR (6/6).
Conclusion: Very high tumor doses with excellent response rates are achievable in radiation sub-segmentectomy. However, ensuring complete response still requires ≥95% tumor volume receiving established dose thresholds.