ESTRO 2020 Abstract book

S1044 ESTRO 2020

Purpose or Objective The purpose of this study is to check the implementation status of the quality control of high energy linear accelerators used in the Korean radiation therapy center at the national level and to prepare institutional improvements based on the results. Material and Methods We conducted remote quality audits at the national level (KOLAS, Korea Laboratory Accreditation Scheme) over 2017 and 2018 for the total photon energy of LINAC used in radiotherapy by 91 Korean institutions. For this, RPL dosimetry system and film dosimetry system were established. The output dose using RPL Glass dosimeters was measured and for the measurements of geometric accuracy (field size agreement and gantry, collimator, and couch rotational isocentric verification) using Gafchromic film (RTQA2) each water equivalent phantom was used. (Fig. 1, Fig. 2) All external audits were performed according to the respective procedures.

Results The output dose was measured for 321 photon beam energies (3 for 4 MV, 161 for 6 MV, 98 for 10 MV, 59 for 15 MV) generated from 164 LINACs. It was evaluated to be within the tolerance level (ICRU recommendation, within ± 5%) for all energies. (Fig. 3 to Fig. 6, and Table 1) In order to confirm the mechanical accuracy of the photon beam, the radiation field size (tolerance level within a 2mm discrepancy) and the couch, collimator, and gantry rotational isocentric verification (tolerance level within a tangential diameter of ± 2 mm) were evaluated respectively. All analyzes were performed using DOSELAB, a film dosimetric software. As a result, the field size and the couch rotational isocentric verification was evaluated to be within the acceptable level in all LINACs. However, in the case of the gantry and collimator rotational isocentric verification of the 161 units, two units out of the permissible level were obtained. (Fig. 7 and 8)

Conclusion These results confirm the quality management status of LINACs used in radiation therapy in Korea. It can help to establish a national quality control system for radiotherapy according to the proposed quality control standard procedures. The results of this study are expected to be applied to independent quality audits of radiation therapy devices such as Tomotherapy, CyberKnife, Proton, Carbon, Brachytherapy, and etc. Finally, through the independent national quality audits at the SSDL level, stable use of high- energy radiation for radiation therapy can be achieved. PO-1781 Development and implementation of an End- to-End test for small animals radiation research I. Silvestre Patallo 1 , A. Subiel 2 , A. Westhorpe 3 , C. Gouldstone 4 , A. Tulk 5 , R.A. Sharma 3 , G. Schettino 6 1 National Physical Laboratory, Medical Radiation Physics, Teddington, United Kingdom ; 2 National Physical Laboratory, Medical Radiation Sciences, Teddington, United Kingdom ; 3 University College London, Translational Radiation Oncology- Cancer Institute, London, United Kingdom ; 4 National Physical Laboratory, Medical Radiation Science, Teddington, United Kingdom ; 5 Xstrahl, Development Department, Camberley, United Kingdom ; 6 National Physical Laboratory and University of Surrey, Medical Radiation Science and Faculty of Engineering and Physical Sciences Department of Physics, Teddington, United Kingdom Purpose or Objective Part of the efforts from the Clinical and Translational Radiotherapy working group (CTRad) are concentrated to improve accuracy for preclinical irradiations with small animal radiation research platforms (SARRP). This work aimed to design and implement an End-to-End test that would allow for a better understanding of the achievable levels for absolute dosimetry in relevant irradiation conditions for SARRP, by comparing the results among five participant UK institutions. Material and Methods