Development of an X-ray imaging camera for targeted radionuclide therapy with astatine-211

The alpha-particle targeted radionuclide therapy (TRT) has been actively investigated for cancer treatment, and astatine-211 (211At) is one of the promising alpha-particle emitters. To evaluate the efficacy of radioactive pharmaceuticals, it is necessary to understand the 211At distribution in a body to accurately assess radiation dose in the targeted cells. In this study, an X-ray imaging camera was developed to investigate an in vivo 211At imaging technique for the alpha-particle TRT, especially to apply for small animal investigations. The design of the X-ray imaging camera was optimized to measure Po K X-rays (77-92 keV) emitted during 211At decay. It comprised a monolithic NaI(Tl) scintillator, a position-sensitive photomultiplier, and a tungsten pinhole collimator. The intrinsic performance evaluation of the position-sensitive X-ray detector exhibited good energy resolution, spatial resolution, and response uniformity. Using point-like 211At sources, the 211At distribution was successfully obtained by the X-ray camera with a useful field-of-view of 20.4 x 20.4 mm2, a system spatial resolution of 1.6 mm, and a sensitivity of 2.4 x 10-4, equivalent to 101 cps/MBq, on the collimator axis at a 12.5 mm distance. This study demonstrated the imaging capability of 211At with high sensitivity and spatial resolution by the X-ray imaging camera with a pinhole collimator.