Evaluation on the radiation exposure from activated wedge filter

In the process of photon treatments, linear accelerators with energies higher than 10 MV produce neutrons through the (γ, n) interactions with the composite materials of the linac head md these materials further produce the induced radiations. We investigate the possible risks from these induced radiations especially in the wedge filters to the radiation workers. Wedge filters are used to modify the isodose profiles in the radiation treatment using the linear accelerator and always be handled by the radiation workers. For the background radiation, we measured the radiation in both the waiting room and the outside of the building for two hospitals, S and H. The results of S hospital were 0.11 μSv/hr and 0.10 μSv/hr for waiting room and outside respectively, and in the case of H hospital, they were 0.12 μSv/hr and 0.11 μSv/hr. Using a survey meter, we measured the radiation from wedge filters inserted in 10 MV and 15 MV Siemens linear accelerators. The time series measurements were done in ∼1 minutes after exposure of 5 Gy of monitor units for the field size of 25 x 25 cm2. The starting value of 10 MV machine was about 3.26 μSv/hr, which was three times higher than that of 10 MV. The measured radiation was from 2'8Al and 53Fe with a half life of 3.5 min. If the treatment patients are 20-50 per day and the number of process of wedge filter change per patient is one or two, the annual dose equivalent is 0.08-0.4 mSv for 10 MV, and 0.27-1.36 mSv for 15 MV, which are in the range of dose equivalent limits of radiation workers.