Development of a radon and radon daughter monitoring systems for detection of Radium-223 daughter radionuclides in air

Objectives: 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 concentrations of these radon daughters in the air were difficult to measure. To solve the problems, we developed the radon and radon daughter monitoring systems to detect Rn-219 around patients during alpha radionuclide therapy.

Methods: For the measurements of radon concentration, we developed a scintillation cell-type detector radon detector. It was made of a sphere chamber 20 cm in diameter the inside of which was painted with ZnS(Ag) scintillator to detect the alpha particles from radon by detecting her daughter radionuclides produced in the chamber. Measurements of daughter radionuclides of radon were conducted by an electrostatic collecting-type detector. It was made of a scintillation detector using a thin plastic scintillator combined with a photomultiplier tube (PMT). Since negative high voltage was supplied to the photocathode of the PMT, the daughter radionuclides of Rn-222 (Po-218 and Po-214) and Rn-219 (Po-215 and Bi-211) accumulated on the plastic scintillator covered with aluminized Mylar because these daughter radionuclides are positively charged by the previous alpha decays.

Results: While the Ra-223-administered patients were in a room, 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.

Conclusions: We could successfully develop radon daughter monitoring systems that could detect the daughter radionuclides of Rn-219 accumulated around the patients.

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