Dependence between the size of the treatment room and the fluence of neutrons undesirable in radiotherapy for the high-energy therapeutic X-Rays generated by the linear medical accelerator

Abstract

The medical linear accelerator is a very commonly used therapeutic equipment in modern radiotherapy. The high-energy X-ray beams generated by such accelerators induce neutrons undesirable in the radiotherapy treatment. The neutron radiation is produced mainly in (,n) and (,2n) reactions. The problem of induced neutron radiation during emission of high-energy X-ray beams is known but it is still unsolved. The undesirable neutrons induce radioactivity inside the treatment room as well as they are the factor of the additional total body dose to patients. The induced radioactivity gives its contribution to the dose to staff operating an accelerator. The influence of sizes of the treatment room on the neutron fluence in the vicinity of the accelerator was investigated in the presented studies. Two methods were applied. The main one was the Monte Carlo computer simulations based on the Geant4 code. These Monte Carlo calculations were verified by means of the neutron activation method with the use of the indium foil and cadmium in the range of thermal and resonance energies. The performed studies are indicative that there is a sensitive dependence between the treatment room size and the neutron level. The greater neutron fluence was observed for a less treatment room.