#8. Radium-223 treated primary patient bone biopsy analysis: Macro to microscale analyses and dosimetry

531 Objectives: In nuclear medicine and radiation oncology, dosimetry has an important role in guiding clinical trial design in order to maximize the likelihood of a successful, minimally toxic intervention. For alpha particle-emitting radiopharmaceuticals, personalized dosimetry is challenging because of local activity distribution heterogeneity, the short range of alpha particles and challenges in noninvasive imaging. Existing small-scale dosimetry methods predominately rely on standardized anatomical models of healthy tissues. Moreover, the fundamental assumption in their approach is of a uniform distribution of emitters in the source volume and a calculation that gives the average absorbed dose to the target volume. To overcome these problems, we investigated the microscopic distribution of 223Ra in bone biopsies from patients with metastatic castration-resistant prostate cancer (mCRPC). Materials & Methods: Bone biopsies were obtained from four mCRPC patients under fluoroscopic guidance following a bone scan, 24h after injection of 223Ra. Blood samples were also collected at the same time. The 223Ra activity in each biopsy and blood sample was measured with a gamma-counter and evaluated with a high purity Germanium detector (Figure, a and c). Microsctructure images of the tissue was performed for each biopsy by µCT (20 µm resolution) (Figure, b). The samples were then cryosectioned and autoradiography was performed on the sections using a Cyclone PhosphorImager. The same sections were stained with hematoxylin and eosin (HE with other investigational alpha particle emitting therapies; to guide clinical application with adapted dosing; and ultimately for more effective application.