Detecting the optimal patient-specific radiation dosimetry in Yttrium-90 microsphere therapy

Objectives: This study aims to detect the maximum permissible activity (MPA) in patients with unresectable liver metastasis and hepatocellular carcinoma treated with Yttrium-90 (Y-90) microspheres and to evaluate the absorbed radiation doses with patient-specific dosimetry methods. Materials and methods: A total of 31 patients (20 males, 11 females; mean age 47±0.2 years; range, 32 to 62 years) were applied dosimetry. Empiric, body surface area (BSA), Medical Internal Radiation Dose (MIRD) and partition internal dosimetry models were used to calculate the MPA to deliver the maximum absorbable dose to the tumor while reducing the absorbed dose by the critical organs. Results: Mean Y-90 activity was 57483±7.7 megabecquerel (MBq) for empiric model, 1806.04±1.37 MBq for BSA, 1649.60±1.3 MBq for MIRD, and 1658.71 MBq for partition. Mean absorbed dose calculated according to empiric model was 40.14±0.20, 197.62±0.45 and 7.39±0.08 gray (Gy) for normal liver, tumor and lung, respectively. Mean absorbed dose calculated according to BSA was 33.61±0.18, 167.83±0.41, 6.39±0.08 Gy for normal liver, tumor and lung, respectively. Mean absorbed dose calculated according to MIRD was 29.63±0.17, 125.62±0.36 and 5.67±0.07 Gy for normal liver, tumor and lung, respectively. Mean absorbed dose calculated according to partition model was 29.82±0.17, 126.72±0.36 and 5.72±0.07 Gy for normal liver, tumor and lung, respectively. Conclusion: Since the MPAs calculated according to empiric and BSA models will lead to organ toxicity by forming high amounts of absorbed doses at critical organs, these models are not appropriate approaches for dosimetry. On the other hand, MIRD and partition models are the most successful methods for internal dosimetry applications.