Shielding Design Basis and its Calculation of High Energy Medical Linac Installed in Bangladesh Atomic Energy Commission, Bangladesh

Abstract

High energy medical linac from Varian Medical Systems of model Clinac iX is installed in Bangladesh Atomic Energy Commission with dual photon energies (15 MV and 6 MV) and five electron energies upto 18 MeV. This machine is used to treat cancer patients either in electron or photon mode depending on the position of the malignant tissue. As the particles energies are in MeV range, special measures are taken into account for designing linac bunker. In this study, maximum photon energy is considered for shielding design. Other two particles i.e., electron and neutron are not considered due to their low penetration depth. As physicists the aim for us is to consider and calculate the shielding so that to protect the people and the stuff. Protection is required against three types of radiation such as, primary radiation (from the patient), scattered radiation (from the patient) and leakage radiation (from the linac head). To save the radiation worker from these three types of radiations, primary wall and secondary wall thickness, primary wall width and roof thickness are calculated. These calculations are done by empirical equations known as NCRP calculations using data in tabular form. These empirical equations are similar to those developed by Mutscheller. The primary and secondary barrier thickness for 15 MV and 6 MV photons are 2.84 m, 2.31 m and 0.93 m, 0.83 m respectively. Radiation survey reports are found to be below 10 µSvhr-1 at six different locations for different gantry positions. This paper reveals what measures have been taken to protect the occupational workers and public from linac radiation hazards.