Evaluation of the radiation protection at the new radiotherapy treatment department at the University Hospital of Umeå

Abstract: At the University Hospital of Umeå, NUS, a new radiation treatment department is being built. The purpose of this master thesis is to evaluate the actual radiation protection outside three out of five treatment rooms in the building, including two Varian and one Siemens accelerator, and to verify that the radiation limits for the staff and the general public, stated by the Swedish Radiation Safety Authority, are obeyed. The evaluation of the radiation protection shielding is made through measurements. The nominal photon beam energies 6 and 15 MV (dose rates up to 500 MU/min) can be used, which means that both photons and neutrons will contribute to the effective dose. For the photon measurements, two different GM counters have been used and for the neutron measurements a Neutron detector with a polyethylene moderator and a 3He recoil proton counter tube was applied. The thesis also includes a literature study of the photon and neutron energy spectra outside the treatment rooms in order to check that the measurement equipments are suitable to use. The measured doses of the radiation shielding are below the radiation limits per week and year but the measurements indicate too high values per hour, i.e. momentary dose rate, at the height of isocenter of the primary walls and at the gap under the door for all three accelerators. The rooms with the Varian accelerators also show too high values per hour at the secondary wall where the door is attached. However, the limiting value per hour is only a recommendation and no extra reinforcement in therefore required. Nevertheless, one should avoid placing a workplace, for example a writing desk, close to the secondary and primary walls.