Abstract No. 154 Using Post–Yttrium-90 PET/CT To Identify Tumors More Likely to have Complete Pathologic Necrosis After Radiation Segmentectomy for Hepatocellular Carcinoma

To evaluate complete pathologic necrosis (CPN) following 90Y radiation segmentectomy using resin microspheres for hepatocellular carcinoma (HCC), and the post 90Y PET/CT characteristics associated with CPN. All HCC patients receiving 90Y radioembolization from 2014 to June 2023 (n=176) were assessed in this retrospective, institutional review board–approved study. Patients undergoing radiation segmentectomy (1-2 segments treated using single compartment MIRD model) followed by resection or transplant were included (n=13). 90Y procedure characteristics and histology results were collected. Microsphere distribution per cc were calculated based on a previously described formula. Minimum absorbed dose to 50% of the tumor (D50) and volume of tumor receiving < 100 Gy (V0-100) were calculated on post-90Y PET/CT. Median age was 69 years (59–70), 92% were male, and median tumor size was 2.5 cm (1.9–4.5). 9/13 (69%) were BCLC-A, and 4/13 (31%) were BCLC-C due to portal vein tumor thrombus. The median target perfused volume was 290 cc (268–516). Median prescribed average absorbed dose in the perfused volume was 250 Gy (200–300), with a median prescribed activity of 1.8 GBq (1.1–2.4) resulting in delivered dose of 235 Gy (156–281). The majority (8/13 [62%]) underwent resection, with the remaining 5/13 (38%) undergoing transplantation. Post-surgical pathologic examination demonstrated CPN in 8/13 (62%) of patients. Patients who achieved CPN had a lower tumor volume (20 cc [9-33] vs. 80 cc [43–118), p = 0.01), but no statistical difference in prescribed dose (300 Gy [238–300] vs. 200 Gy [200–250], p = 0.13) or prescribed tumor spheres per cc (85,931 [54,717–92,670] vs. 46,609 [40,507–58,108], p = 0.16). Post-treatment PET/CT analysis showed the D50 was similar in tumors with and without CPN (218 Gy [184–340] vs. 303 Gy [195–508], p = 0.92). Tumor volume with < 100 Gy was also similar between these groups [CPN: 0.33 cc (0.005–1.6) vs. Not CPN: 8.6 cc (5.3–11.6), p = 0.16]. The microsphere distribution per cc was 54933 (47727–82887) in tumors with CPN compared to 45244 (34986–55887) in tumors without CPN (p=0.41). CPN was achieved in 6/7 (86%) patients with V0-100 of < 2 cc, compared to 1/4 (25%) of patients with V0-100 of >2 cc (p = 0.04). Additionally, CPN was achieved in 4/6 (66%) patients with a D50 > 215 Gy and 6/8 (75%) patients with tumoral microsphere distribution per cc of >45,000. HCC treated with 90Y resin-based radiation segmentectomy results in a high CPN rate. Undertreated tumor volume (V0-100Gy of >2 cc) can be identified on post-treatment PET/CT and predicts CPN.