Measurement and radiation control of α-emitting radium-223 in radionuclide therapy for prostate cancer with bone metastases

Learning Objectives Radium-223 dichloride (Ra-223), an α-emitting radionuclide therapy agent currently called Xofigo (formerly Alpharadin), was developed for the treatment of multiple bone metastases and approved in USA and Europe in 2013 for castration-resistant prostate cancer with symptomatic multiple bone metastases. In recent multi-center clinical trials, Ra-223 improved the outcomes of overall survival, skeletal-related events, pain relief, and quality of life. Considering the impact of Ra-223 therapy in clinical practices, issues concerning measurement and radiation control for Ra-223 still require investigation including daughter nuclides. Here we focus on basic standards in handling Ra-223 in clinical sites.

A property of Ra-223 and its daughters of Rn-219, Po-215, At-215, Pb-211, Bi-211, Po-211, Tl-207, and stable Pb-207. is that, in addition to emission of α and β particles, it emits γ-photons and characteristic X-rays that are detected by conventional GM detectors and NaI(Tl) scintillator detectors, and can be handled even without a dedicated α detector. We therefore propose standard procedures for measuring Ra-223 emission, and demonstrate our spectrum analysis findings determined using High Purity Germanium detectors (HP-Ge), as well as findings with GM and NaI(Tl) scintillator detectors. The key issues are as follows: 1) a rationale for Ra-223 in radionuclide therapy for multiple bone metastases; 2) HP-Ge spectrum analysis; 3) GM and NaI(Tl) scintillator detector counting, considering parameters such as time constants, surveys, and speed; 4) key issues for Ra-223 use in clinical sites, such as facility prerequisites and precautions; 5) dose calibrator and quality control for radionuclide settings. In conclusion, Ra-223 should adequately be handled according to standard procedures in association with seamless care for patients with symptoms caused by multiple bone metastases.

Research Support This work was supported by JSPS KAKENHI Grant Number 25461854 and MHLW Grant Number 201232024.