Ra-223 has recently been introduced to alpha radionuclide therapy. According to the decay scheme of Ra-223, an inert gas, Rn-219 is released from patients during alpha radionuclide therapy and its daughter radionuclides may accumulate around the patient. However, the concentration of these radon daughters during alpha radionuclide therapy was not obvious. Here, we first detected the radon daughters of Rn-219 around patients during alpha radionuclide therapy. While the Ra-223-administered patients were in a room for ~1.5 hours, the radon daughter concentration increased to 4 to 5 times higher than without the patients. When the patients were in the room, the energy spectra of the alpha particles in the air showed the peak of the radon daughter of Rn-219, Bi-211 (6.6 MeV), which was different from that without the patients. We conclude that the daughter radionuclides of Rn-219 are accumulated around the patient, and the concentration was higher than that of the natural radon daughters. However, the increase in levels of alpha emitters, while detectable, is lower than the daily variations and thus is likely not a source of concern for radiation exposure.
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