Study on Radioactivity Induced by Various Patient-specific Devices in Proton Therapy

Abstract

It is important to estimate the radioactivities induced by the patient-specific devices installed near the patient skin because it was directly expose the patient during the treatment. This study evaluated the radioactivities induced by the brass collimator and PMMA range compensator in the proton beam, and identified the radionuclide produced by the nuclear interactions of the proton beam with the patient-specific devices. When the radiation dose was evaluated at the highest energy region, the exposure of patients by the radioactivities in the patient-specific devices was usually very low when compared to the dose limit in Korea. PMMA, which is mainly composed of oxygen and carbon, is used to fabricate the range compensators. The aperture of the used brass, which is mainly composed of zinc and copper, determines the boundary between the tumor and normal tissue in the body of the patient. Furthermore, these materials are widely used for phantoms and apertures. The radioactivities induced in brass and PMMA after the irradiation of proton beam was evaluated. The radionuclides in brass and PMMA produced by protons and neutrons were the major cause of radiation exposure for patients in proton therapy. In both case of PMMA and brass, 1 hour later their activities reach about 2% of the initial values. The amount of radiation dose is small due to the short treatment time, and the radiation exposure of patients is negligible when compared to the total dose to the patient.