First demonstration of portable Compton camera to visualize 223-Ra concentration for radionuclide therapy

Radionuclide therapy (RNT) is an internal radiation therapy that can selectively damage cancer cells. Recently, the use of alpha-emitting radionuclides was initiated in RNT owing to its dose concentration and short range. In particular, 223 Ra is widely used for bone metastasis of prostate cancer. Despite its potential for clinical applications, it is difficult to determine whether a drug has been properly delivered to the target lesion. As such, we propose a new method of monitoring nuclear gamma rays promptly and simultaneously emitted from 223 Ra as alpha decay using a high-sensitivity Compton camera. We first observed a small bottle of 223 Ra solution with a total radioactivity of 0.56 MBq. The reconstructed image converged at the correct position with a position resolution of ∼ 20 mm at a plane 10 cm in front of the camera. Next, we observed a phantom consisting of three spheres with diameters ranging from 13 to 37 mm filled with 223 Ra solution (9 kBq/mL) and then surrounded by a ∼ 20-cm layer of water. A three-dimensional (3D) image was constructed by rotating the Compton camera around the phantom. Images were then acquired from eight directions at 30-min intervals, respectively. Although the image resolution remained limited at 351 keV, three spheres were resolved at the correct position in the 3D image with their relative intensities. Thirdly, we observed the body of a patient for 10 min and reconstructed almost the same accumulation as the image acquired by a single-photon emission computed tomography (SPECT) system for 30 min. While the spatial resolution of the Compton camera was worse, DOI-CC obtained a wider image in a shorter time. Finally, we discuss current problems and plans for improving sensitivity and angular resolution for future clinical applications.