Sasicha Manupipatpong, MD
Integrated Diagnostic and Interventional Radiology Resident
Johns Hopkins University
Rebecca Krimins, DVM
Assistant Professor of Radiology and Radiological Science
Johns Hopkins University School of Medicine
Clifford Weiss, MD, FSIR, FCIRSE
Professor of Radiology and Biomedical Engineering
Johns Hopkins Univeristy School of Medicine
This study evaluated histopathology and compared the use of PET/CT and MicroCT dosimetry during yttrium-90 (90Y) radioembolization (RE) in canine models with astrocytic gliomas.
Materials and Methods:
Five clinically stable patient dogs (P1-P5) with unilateral, intra-cranial brain masses >1cm in size underwent ipsilateral internal carotid artery RE with 90Y glass microspheres (TheraSphere) 1-3 months after first seizure. Patient dogs received PET/CT 24-hours post-treatment, MRI at 1-, 3-, and 6-month intervals, and serial neurological exams by a veterinary neurologist. At time of natural death or euthanization, MicroCT dosimetry and histopathologic analyses were performed.
P5 had neurologic defects on presentation and a subsequent seizure 5 hours post-treatment leading to ventilatory arrest and expiration at 15 hours post-treatment. P1-P4 had a mean survival time of 565 days with mean time from treatment to return of seizure activity of 301 days. Post-treatment PET/CT reported an average dose to masses in P2-P4 of 46.9, 40.7, and 62.1 Gy while the dose to uninvolved brain tissue was 54.1, 33.9, and 57.3 Gy, respectively. Post-mortem MicroCT dosimetry demonstrated an average dose to masses in P2–P4 of 52.5, 48.2, and 68.1 Gy while the dose to uninvolved brain tissue was 28.2, 14.5, and 42.3 Gy, respectively. Follow-up MRI demonstrated decreased tumor size at 1 month (P1-P4) and 6mo (P1, P3, P4). Histopathology for P2-P5 confirmed the presence of high-grade astrocytic gliomas with rare mitotic figures and absence of glomeruloid vascularization.
90Y RE is feasible in the canine model, delivering 2-3x higher dose to mass compared to normal parenchyma based on microdosimetry. Patient dog mean survival time (565 days) was 9x that of medical symptom management alone (63 days – Moirano et al.). Compared to PET/CT, MicroCT reported higher 90Y dose to tumors but lower dose to uninvolved cortex. Due to the small mass size, sphere concentration over time as the tumor shrank, and limited imaging resolution, PET/CT likely underestimated the tumor doses. Conversely, PET/CT has been shown to overestimate dose at low activity concentrations seen in normal brain tissue and thus reported higher doses in uninvolved cortex (Willowson et al.). MicroCT dosimetry is a more appropriate method to compare 90Y RE dose delivery in canine brain masses.