Correlation Between CT/MRI and Bremsstrahlung SPECT of 32P After Radioembolization of Hepatic Tumors

Background/Objective: Radioembolization (RE) is a minimally invasive transcatheter therapy through which radioactive microspheres are infused into the hepatic arteries and selectively implanted within the tumor arterioles. Some therapeutic agents are particles incorporating pure β emitter elements (90Y, 32P) and do not have gamma radiation. Bremsstrahlung imaging of these radiotherapeutic agents confirms distribution of the radiotracer in hepatic tumors or probable extrahepatic deposition of radiopharmaceuticals and helps the physician to predict the patient's response to RE therapy. The aim of this study was demonstration of 32P images and its correlation with CT/MRI findings. Patients and Methods: Ten patients with variable types of hepatic tumors treated with intraarterial injection of 32P were included in this study. 24-72 hours after radiotracer administration, bremsstahlung SPECT imaging was performed in all patients with a single head gamma camera equipped with a medium energy collimator. Energy window setting of 100 keV±25% was selected. Reconstructed images were evaluated by two nuclear medicine specialists and one radiologist, and based on compatibility of 32P images with CT/MRI, a grading scale from 1 to 4 was used to express their correlations. Results: By selecting optimized parameters for bremsstrahlung SPECT images of 32P, we could obtain good quality images. In nine patients, 32P distribution in the liver was correlated with anatomical findings of CT/MRI. Conclusion: RE is appropriate to deliver high radiation doses to liver tumors with minimal accumulation in the normal liver tissue. Bremsstrahlung imaging is a useful method to confirm proper distribution of the radiotherapeutic agent, which has good correlation with anatomical findings.