Quantitative measurement of 219Rn radioactivity in exhaled breath from patients with bone metastasis of castration-resistant prostate cancer treated with 223RaCl2.

Background: The α-emitting radionuclide radium-223 (²²³Ra) is widely used for the treatment of bone metastasis in patients with castration-resistant prostate cancer. However, ²²³Ra decays into radon-219 (²¹⁹Rn) which is a noble-gas isotope, and ²¹⁹Rn may escape from patients treated with ²²³Ra via their respiration. In this study, we quantified the amount of ²¹⁹Rn contained in the breath of patients treated with ²²³Ra to estimate its effect on the internal exposure dose of caregivers. Methods: A total of 12 breath samples were collected using a breath collection bag from a total of six patients treated with ²²³RaCl₂. Approximately 300 mL of exhaled breath was collected in a breath bag at 1 min and at 5 min after the start of ²²³RaCl₂ administration. The contents of each bag were measured using an HPGe detector, and the amount of ²¹⁹Rn was quantified based on the detection of the γ peak of ²¹¹Bi, which is a descendant nuclide of ²¹⁹Rn, persisting in the breath bag. The effective dose to caregivers arising from the inhalation of ²¹⁹Rn was estimated by referring to the scenario for the calculation of release criteria established for ¹³¹I therapy in Japan. Results: A small peak for the 351-keV γ ray of ²¹¹Bi originating from the exhalation of ²¹⁹Rn was observed. Using the observed γ peak of ²¹¹Bi, the average amounts of ²¹⁹Rn per unit breath volume at 1 min and 5 min after the start of ²²³RaCl₂ administration were calculated as 90 ± 56 Bq/mL and 28 ± 9 Bq/mL, respectively. The effective dose of ²¹⁹Rn to caregivers was estimated to be 3.5 μSv per injection. Conclusions: The amount of ²¹⁹Rn in the exhaled breath of patients treated with ²²³RaCl₂ was quantitatively calculated using breath collection bags. The internal radiation exposure of caregivers from ²¹⁹Rn in the exhaled breath of patients treated with ²²³RaCl₂ is relatively small. [ABSTRACT FROM AUTHOR]