Evaluating Safety and Dosimetry of SBRT following 90Y for Hepatocellular Carcinoma

Abstract

Liver directed therapy is fundamental in the treatment of HCC. SBRT is the only non-invasive local therapy characterized by precise target delineation and accurate, quantifiable dosimetry. Often, SBRT is utilized following interventional therapy; however, there is a lack of data reporting safety and outcomes of patients receiving liver SBRT after yttrium-90 (90Y). We performed a safety and dosimetric evaluation in our series of HCC patients who received SBRT after 90Y by compiling post 90Y PET imaging fusions with SBRT treatment plans for accurate quantification of liver exposed to both SBRT and 90Y. An institutional review board-approved liver SBRT registry of 197 patients was used for data collection. All patients had post-90Y PET (measuring Bremsstrahlung component of 90Y) fused to SBRT treatment planning CT creating composite plans for dosimetric analysis. Volume of ablated liver was estimated using the sharp gradient edge of post-90Y PET, and the 30 Gy isodose line for SBRT (V30). Clinical and laboratory follow up 3 months post SBRT were used to evaluate safety. Changes in chemistry and hematology related to hepatic function, using CTCAE v4.0, were analyzed. Sixteen patients with non-metastatic HCC and prior 90Y were treated with SBRT to 18 intrahepatic sites. Patients received 23 prior 90Y administrations; six patients were treated twice and one patient treated three times. Child-Pugh (CP) category at SBRT was A in 12, and two each of B and C. SBRT dose was 35-50 Gy in 3-5 fractions (median 50 Gy/5). Median time between 90Y and SBRT was 4.6 months (range 1.3-34.8). Mean follow up was 14 months, and 11 patients were alive at analysis. Treatment intent was definitive for 13 patients and downstaging in 3. Mean total liver volume was 2,000 cc (range 986-3304), SBRT PTV 209 cc (range 26-494), and individual 90Y treatment volume 308 cc (range 36-1477). Liver ablative results summarized in Table 1.Abstract SU_13_2123; Table 1Mean valueMean %RangeV30 liver (SBRT)273 cc13.7%36-739 cc (3-34.8%)90Y volume (sum)436 cc22.6%95-1512 cc (3.5-52.6%)V30 volume within prior 90Y93 cc33.2%0-306 cc (0-75%) Open table in a new tab Laboratory data was available for 75% of patients. At 3 months post SBRT there were no new grade ≥2 changes from baseline in bilirubin, hemoglobin, INR, AST, ALT, and albumin in CP-A/B patients. The two CP-C patients, who had higher 90Y volumes and more overlap of 90Y with V30, demonstrated clinically significant hepatic decompensation. Although toxicity was noted, both patients were successfully down-staged within Milan then rescued with transplant 10 and 15 weeks post SBRT. This is the first series to incorporate PET delineation of 90Y ablation distribution in a composite plan with SBRT. Our experience of CP-A /B patients demonstrates minimal toxicity, but notable decompensation in CP-C patients. SBRT can be an effective tool to downstage within Milan but extra caution is warranted in this group, such that risk matches treatment intent, especially in patients that may not be rescued with transplant.