Effectiveness of radiation protectors to reduce occupational radiation dose of medical staff when performing radioligand therapy with 177Lu

Recently, the radioactive nuclide ¹⁷⁷Lu has been applied to clinical radioligand therapy. The β-rays emitted from ¹⁷⁷Lu are used for radiation therapy. Although this nuclide also emits γ-rays that can be used to image radioactive isotope distributions, it causes an exposure dose risk to medical staff who operate the radioligand therapy. This study investigates the radiation-shielding effectiveness of lead protectors during ¹⁷⁷Lu radioligand therapy, based on γ-ray spectra. Both simulations and experimental measurements were conducted to obtain spectra of γ-rays penetrating lead shields. The corresponding air kerma values were calculated from the obtained γ-ray spectra, and the dose reduction factor (DRF) was evaluated. The study found that a lead thickness of 2.0 mm achieves a DRF of 90 %. However, ¹⁷⁷Lu also contains several low-energy γ-ray components (e.g., 57 keV and 113 keV), suggesting that thinner lead could be effective for shielding them. We then found that even thicknesses in the range of 0.07 mm–0.75 mm, which have been used as actual protectors, were effective. More specifically, a DRF of 50–55 % was obtained with a protector having a lead-equivalent thickness of 0.50 mm. In conclusion, we propose the use of lead protectors for occupational dose reduction when performing radioligand therapy with ¹⁷⁷Lu.