Abstract
Targeted alpha therapy is attracting significant attention for the treatment of intractable tumors and the development of efficient gamma cameras to evaluate the biodistribution of alpha emitters is expected. 211At, which is a commonly used alpha emitter in Japan, emits characteristic X-rays whose energy is distributed between 77 and 92 keV. We evaluated the biodistribution of this alpha emitter by effectively acquiring these photons. Because the performance of a gamma camera strongly depends on that of collimators, we designed and manufactured high-performance collimators by processing pure tungsten, which can shield radiation more effectively than lead, using state-of-the-art three-dimensional (3D) printing technology. We successfully fabricated a parallel-hole collimator with a honeycomb structure with a hole size of 1.0 mm and septal thickness as thin as 0.07 mm. When a point source of 133Ba that emits photons with the energy of 81 keV, similar to that of characteristic X-rays emitted from 211At, was imaged using this collimator, spatial resolution of this collimator was as short as 5.7 mm and its efficiency was as good as 1.42×10−4; these results are superior to those of commercially available clinical scanners. We also demonstrated that our collimator could successfully depict a shape of the object by imaging a mouse thyroid gland after the injection of the 211At solution. These results suggest that excellent collimators made of pure tungsten could be used to monitor targeted alpha therapy using 211At.
