Limitations of Body Surface Area-Based Activity Calculation for Radioembolization of Hepatic Metastases in Colorectal Cancer

Purpose: To calculate absorbed radiation doses in patients treated with resin microspheres prescribed by the body surface area (BSA) method and to analyze dose-response and toxicity relationships. Materials and Methods: A retrospective review was performed of 45 patients with colorectal carcinoma metastases who received single-session whole-liver resin microsphere radioembolization. Prescribed treatment activity was calculated using the BSA method. Liver volumes and whole-liver absorbed doses (D-WL) were calculated. D-WL was correlated with toxicity and radiographic and biochemical response. Results: The standard BSA-based administered activity (range, 0.85-2.58 GBq) did not correlate with D-WL (mean, 50.4 Gy; range, 29.8-74.7 Gy; r = -0.037; P = .809) because liver weight was highly variable (mean, 1.89 kg; range, 0.94-3.42 kg) and strongly correlated with D-WL (r = -0.724; P < .001) but was not accounted for in the BSA method. Patients with larger livers were relatively underdosed, and patients with smaller livers were relatively overdosed. Patients who received D-WL > 50 Gy experienced more toxicity and adverse events ( > grade 2 liver toxicity, 46% vs 17%; P < .05) but also responded better to the treatment than patients who received Dwi, < 50 Gy (disease control, 88% vs 24%; P < .01). Conclusions: Using the standard BSA formula, the administered activity did not correlate with D-WL. Based on this short-term follow-up after salvage therapy in patients with late stage metastatic colorectal carcinoma, dose-response and dose-toxicity relationships support using a protocol based on liver volume rather than BSA to prescribe the administered activity.