Patient Specific 3D Image-Based Radiation Dose Estimates for 90Y Microsphere Hepatic Radioembolization in Metastatic Tumors

Abstract

Introduction: Hepatic brachytherapy using either resin or glass 90Y microspheres is an established therapy for unresectable primary and metastatic tumors. Unlike conventional brachytherapy, microsphere brachytherapy has no software currently available for pretreatment evaluation and radiation planning. A non-MIRD radiation dose calculation approach is desired to accurately utilize spatial relationships in the liver and tumor distribution. Materials and methods: A newly developed software tool employing the technetium-99m macro aggregated albumin (99mTc-MAA) SPECT 3-D dataset and CT scan was used to estimate the likely absorbed dose in normal liver and tumor tissue from 90Y microsphere brachytherapy (radioembolization). Monte Carlo algorithms were utilized to maximize true 3D dose estimates for each patient's unique liver and tumor geometry. Clinical correlation was completed regarding toxicity, imaging response, and complications as an independent measure of the software's usefulness in predicting radiation effects. Comparisons were made to MIRD, Body Surface Area method, and physician prescription for 90Y activity. Results: The software performed accurately in estimating absorbed dose in phantom testing. Patient data from 50 consecutive patients with metastatic tumors (26 colon, 24 neuroendocrine) to the liver receiving 59 radioembolization treatments were studied. The software estimate of median normal liver and tumor absorbed doses were 27.6 Gy and 41.2 Gy, respectively. Conclusions: The use of pretreatment 99mTc-MAA SPECT co-registered to a CT scan provides useful and unique data for a newly developed non-MIRD, Monte Carlo-based radiation dosimetry software program in 90Y microsphere brachytherapy. Software estimates of radiation dose preserving critical spatial information in the liver and tumors appeared reasonable based on clinical outcomes. Further testing and refinement of the software interface is ongoing with plans to distribute it to research organizations.