Optimal radiation shielding for beta and bremsstrahlung radiation emitted by ⁸⁹Sr and ⁹⁰Y: Validation by empirical approach and Monte Carlo simulations

Objective: High-energy beta emitters such as Strontium-89 (⁸⁹Sr) and Yttrium-90 (⁹⁰Y) are becoming increasingly popular nuclear therapy sources in Japan for treating cancer. Various characteristics of materials must be considered when designing radiation protection device for high-energy beta emitters. We empirically measured and simulated dose equivalents of beta and bremsstrahlung radiation arising from ⁸⁹Sr and ⁹⁰Y radiation shielded with various materials and determined optimal shielding materials against these sources. Methods: The dose equivalents of ⁸⁹Sr and ⁹⁰Y determined experimentally using an ionization chamber survey meter were compared with those of Monte Carlo simulations. The relative dose equivalents of beta and bremsstrahlung radiation separately transmitted by changing the thickness of acrylic, aluminum, iron, lead and tungsten shielding materials were simulated. Results: Dose equivalents were consistent between the empirical measurements and the simulation to within ±5 %. Shielding ability was more effective in the order of tungsten, lead, iron, aluminum and acrylic against both ⁸⁹Sr and ⁹⁰Y. The amount of beta and bremsstrahlung radiation transmitted through tungsten and lead was relatively small. Although such high-density material generates much bremsstrahlung radiation, it absorbs the bremsstrahlung radiations. Conclusions: Tungsten was the optimal material for efficient shielding against ⁸⁹Sr and ⁹⁰Y radiation and preferable among operators. The present findings provide useful information about how to define an appropriate shielding strategy for high-energy beta emitters.