3:27 PM Abstract No. 124 MIRD-based activity calculation may improve outcomes over body surface area for resin microsphere radioembolization of metastatic colorectal carcinoma

Abstract

To compare clinical outcomes of resin microsphere Y90 radioembolization (RE) using standard Body Surface Area (BSA) activity prescription versus Medical Internal Radiation Dose (MIRD) prescription for treatment of metastatic colorectal carcinoma (mCRC). Patients with mCRC treated with resin microsphere RE between 2004-2015 were retrospectively reviewed. Standard BSA activity prescription was used from 2004-2012. Starting 2013, MIRD-based activity prescription was substituted, with treated region absorbed doses ranging from 40-65 Gy depending on performance status, liver function, volume of treatment, hypervascularity, and previous treatment history. Radiographic, biochemical, and clinical outcomes were compared. 109 patients (61 M/48 F), median age 60, underwent 118 treatment sessions (96 BSA/ 22 MIRD). 77 underwent whole liver treatment, either single session (72) or staged (5). In the MIRD group, 7 (36%) patients had activity prescribed >10% greater and 3 (15%) had activity >10% lower than what would have been prescribed by BSA. Disease control rate (DCR) by RECIST 1.1 showed a trend favoring MIRD over BSA (71% vs 53%, p = 0.1). MIRD patients showed more mild laboratory toxicity changes at 90 days (CTCAE 4.03, ≤ 2 grade change from baseline) (28% vs 18%, p = NS), but slightly less moderate and severe toxicity changes than BSA patients (>2 grade change from baseline) (0% vs 3%, p = NS). Median changes in serum carcinoembryonic antigen (CEA) in MIRD and BSA groups at 8 weeks after RE were -16% and -8%, (p = NS). Differences in median hepatic progression-free survival did not reach statistical significance (MIRD 150 days vs BSA 90 days, p = 0.5). Likewise, the study was underpowered to show a difference in overall survival (210 vs 321 days, p = 0.4). Using MIRD rather than BSA for activity calculation for resin microsphere Y90 RE of mCRC resulted in increase in dose in 36% and decrease in 15% of patients. Although additional statistical power is needed, consideration of the target liver volume rather than body surface area is a promising approach to increase the efficacy and decrease the toxicity of resin microsphere RE.