Assessment of emission data and transmission factors supporting radiation protection in the use of ²²⁵Ac.

Abstract

Purpose²²⁵Ac is the most promising alpha emitter for radiopharmaceutical therapy. Labeling PSMA, it showed to be effective in the treatment of prostate cancer and research is undergoing in order to improve its production capacity. Currently, there are still few data published concerning operational radiation protection in its use, both in clinics and in radiopharmacy, and even some basic data are not readily available. This papers aims to estimate the emission gamma-ray constant of ²²⁵Ac when at equilibrium with its descendants, and the transmission factors for a broad beam of the gamma-rays emitted by ²²⁵Ac and its descendants.Materials & methodsMonte Carlo simulations were performed using FLUKA 4.2, considering firstly the source in air, in absence of any shielding, and secondly by adding an increasing thicknesses of Lead, Concrete or Tungsten. In order to obtain statistically meaningful results, high-statistics simulations were performed by sampling up to 10¹⁰ primary decay events. As the shielding thickness increased, an appropriate variance reduction technique (importance biasing) was applied.ResultsThe specific gamma ray emission constant for ²²⁵Ac at equilibrium with descendants resulted (3.26 ± 0.03) × 10-5 mSv/h per 1 MBq at a distance of 100 cm. The transmission factors are presented in detail and data have been appropriately interpolated and fitting parameters are reported.ConclusionsThe attenuation curves show a clear bi-exponential trend: performing shielding calculations by adopting a simple approach based on a single value of Half Value Layer (HVL) or Tenth Value Layer (TVL) cannot provide adequate results. In conclusion, our results may be useful in the design of shielded hot cells or accessories necessary for operational radiation protection.