Retrospective voxel-based dosimetry for assessing the body surface area model ability to predict delivered dose and radioembolization outcome

International audienceThe aim of this study was to quantitatively evaluate the body surface area (BSA) model ability to predict tumor absorbed dose and treatment outcome through retrospective voxel-based dosimetry. Methods: Data from thirty-five hepatocellular carcinoma patients with a total of forty-two resin microsphere radioembolization treatments were included. Injected activity was planned with the BSA model. Voxel dosimetry based on 99mTc-labeled macroaggregated albumin SPECT and 90Y-microsphere PET was retrospectively performed using a dedicated treatment planning system (PLANET® Dose, DOSIsoft SA, Cachan, France). Average dose and dose-volume histograms (DVHs) of the anatomically-defined tumors were analyzed. The selected dose metrics extracted from DVHs were: minimum dose to 50% and 70% of the tumor volume (D50 and D70 respectively) and percentage of the volume receiving at least 120 Gy (V120). Treatment response was evaluated six months after therapy according to the European Association for the Study of the Liver (EASL) criteria. Results: Six month response was evaluated in 26 treatments: 14 were considered as objective response (OR) and 12 as non-responding (NR). 90Y-microsphere PET based retrospective dosimetry evaluation showed a large inter-patient variability with a median average absorbed dose to the tumor of 60 Gy. In 62% (26/42) of the cases, tumor, non-tumoral liver, and lung doses could have complied with the recommended thresholds by increasing the injected activity calculated by the BSA Methods: Average doses, D50, D70, and V120 were significantly higher in OR than in NR. Conclusion: In our population, tumor average dose and DVH metrics were associated with tumor response. However the activity calculated by the BSA could have been increased to reach the recommended tumor dose threshold. Tumor uptake, target and non-target volumes, and dose distribution heterogeneity should be taken into account for activity planning