Quantitative measurement of (219)Rn radioactivity in exhaled breath from patients with bone metastasis of castration-resistant prostate cancer treated with (223)RaCl(2)

BACKGROUND: The α-emitting radionuclide radium-223 ((223)Ra) is widely used for the treatment of bone metastasis in patients with castration-resistant prostate cancer. However, (223)Ra decays into radon-219 ((219)Rn) which is a noble-gas isotope, and (219)Rn may escape from patients treated with (223)Ra via their respiration. In this study, we quantified the amount of (219)Rn contained in the breath of patients treated with (223)Ra 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 (223)RaCl(2). Approximately 300 mL of exhaled breath was collected in a breath bag at 1 min and at 5 min after the start of (223)RaCl(2) administration. The contents of each bag were measured using an HPGe detector, and the amount of (219)Rn was quantified based on the detection of the γ peak of (211)Bi, which is a descendant nuclide of (219)Rn, persisting in the breath bag. The effective dose to caregivers arising from the inhalation of (219)Rn was estimated by referring to the scenario for the calculation of release criteria established for (131)I therapy in Japan. RESULTS: A small peak for the 351-keV γ ray of (211)Bi originating from the exhalation of (219)Rn was observed. Using the observed γ peak of (211)Bi, the average amounts of (219)Rn per unit breath volume at 1 min and 5 min after the start of (223)RaCl(2) administration were calculated as 90 ± 56 Bq/mL and 28 ± 9 Bq/mL, respectively. The effective dose of (219)Rn to caregivers was estimated to be 3.5 μSv per injection. CONCLUSIONS: The amount of (219)Rn in the exhaled breath of patients treated with (223)RaCl(2) was quantitatively calculated using breath collection bags. The internal radiation exposure of caregivers from (219)Rn in the exhaled breath of patients treated with (223)RaCl(2) is relatively small.