Assessment of exposure to X - rays during patient positioning at the proton eye radiotherapy facility at IFJ PAN, Kraków

At the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN, Kraków, Poland) the proton eye radiotherapy facility has recently been developed and is now fully operational. A set of two X-ay RAD-14 Varian medical systems tubes are used to obtain orthogonal images of the patient’s eyeball undergoing radiotherapy with tantalum clips already attached to its surface to delineate the tumour volume. We assessed the dose received by the patient from multiple X-ray exposures during the patient positioning procedure. Measurements of Kair were performed using various types of ionization chambers and MCP-N thermoluminescent (TL) detectors and calculated using the PCXMC code. Good agreement between measurements and calculations was found. The mean absorbed dose to the brain was measured using TL detectors placed inside the head of a Rando anthropomorphic phantom used in simulation of the patient positioning procedure. The measured maximum incident air kerma absorbed during the entire procedure of patient positioning was found not to exceed 7 mGy, while the mean absorbed dose to the brain did not exceed 2 mSv.