Biokinetic modelling of the exhalation of 219Rn gas and its airborne progeny from patients undergoing treatment with 223Ra-dichloride and effective dose estimation for caregivers.

The radiopharmaceutical 223Ra-dichloride (Xofigo®) has been approved for palliative treatment of metastatic castration-resistant prostate cancer. During the treatment and caregiving, patients who received 223Ra-dichloride can exhale the progeny 219Rn, a radioactive gas. This causes a potential risk for medical staff and caregivers who might inhale the 219Rn gas and its airborne decay products. As an addition to the strategies of developing devices for measuring 219Rn gas and its daughter nuclides in treatment rooms, this work tried to estimate the amount of exhaled 219Rn and of its airborne progeny using biokinetic modelling. The biokinetic models and parameters for 223Ra and its progeny 219Rn, as published by the International Commission of Radiological Protection, were adopted for this analysis. Without consideration of room ventilation, the model predicted that the amount of 219Rn gas in the room air can reach a maximum activity of 5.8∙10− 2 Bq at approximately 1.5 min after infusion of one Bq of 223RaCl2. The summed activities of 219Rn and its airborne progeny do not exceed 1.2∙10− 1 Bq per infused Bq of 223RaCl2. In the breathing air of the patients, the activities at 1 and 5 min after the infusion were estimated to be approximately 2∙10− 2 Bq and 1.8∙10− 2 Bq per Bq of 223RaCl2, respectively. The values at 1 min are comparable to the measured results reported in the literature. The effective dose from inhalation of 219Rn gas and its airborne progeny due to a treatment of 4015 kBq of 223RaCl2, was estimated to be 232.6 nSv for medical staff and 7.5 µSv for caregivers.