²²³Ra-dichloride spectrometric characterization: Searching for the presence of long-lived isotopes with radiological...

²²³Ra-dichloride was approved with the commercial name of Xofigo in 2014 for treatment of metastatic castration-resistant prostate cancer. ²²³Ra is obtained by neutron irradiation of ²²⁶Ra yielding ²²⁷Ac, which decays to ²²⁷Th and ²²³Fr, both decaying to ²²³Ra. Since ²²³Ra is predominantly (95.3%) an alpha emitter with a 11.42days long half-life, the radiopharmaceutical, its remnants, the patient, and waste material can be managed and disposed with low radiation protection requirements. ²²⁷Ac is a long-lived (T_1/2=21.77years) beta emitter that demands strong radiation protection measures. In particular waste disposal has to follow the International Atomic Energy Agency (IAEA) and European Commission (EC) regulations. Since ²²⁷Ac is involved in the production of ²²³Ra, an impurity analysis of each batch is required after production. Due to time restrictions, the manufacturer's detection limit (<0.001%) exceeds the one required to assure that ²²⁷Ac concentrations are below direct disposal levels. To improve the detection limit, long-term accurate spectroscopy is required. Alpha and gamma spectroscopy measurements were carried out at the Complutense University Nuclear Physics Laboratory. After twelve months follow up of a sample, ²²⁷Ac concentration was found to be smaller than 10^-9. This allows for direct waste disposal and no additional radiation protection restrictions than those required for ²²³Ra. The presence of contamination by other radioisotopes was also ruled out by this experiment. Specifically ²²⁶Ra, involved in ²²³Ra production as the original parent and with a very long-lived (T_1/2=1577years) alpha emitter, was also below the experimental detection limit.