Dosimetry audits in radiotherapy in the Czech Republic

s / Physica Medica 30 (2014) e1ee15 e14 at the national level with IAEA assistance. The national counterparts conduct the TPS audit at local radiotherapy centres through on-site visits. TPS calculated doses are compared with ion chamber measurements performed in an anthropomorphic phantom for eight test cases per algorithm/beam. The set of pre-defined agreement criteria is used to analyze the performance of TPSs. Results: TPS audit was carried out in sixty radiotherapy centers in eight European countries e Estonia, Hungary, Latvia, Lithuania, Serbia, Slovakia, Poland and Portugal. In total, 190 data sets (combination of algorithm and beam quality) have been collected and reviewed. Dosimetry problems requiring interventionswerediscovered in about10%of datasets. In addition, suboptimal beam modelling in TPSs was discovered in a number of cases. Conclusions: The TPS audit project using the IAEA methodology has verified the treatment planning system calculations for 3D conformal radiotherapy in a group of radiotherapy centres in Europe. It contributed to achieving better understanding of the performance of TPSs and helped to resolve issues related to imaging, dosimetry and treatment planning. DOSIMETRY AUDITS IN RADIOTHERAPY IN THE CZECH REPUBLIC Irena Koniarova, Daniela Ekendahl, Ivana Horakova, Michaela Kapucianova, Vladimir Dufek. National Radiation Protection Institute, Prague, Czech Republic Background: The independent audits in radiotherapy are carried out by the National Radiation Protection Institute as a part of the regulatory authority activity since 1996. The system includes TLD postal audits (external radiotherapy) and on-site audits (external radiotherapy and brachytherapy). TLD audit can be performed in several versions differing in the scope and focus of dose measurements. Basic TLD audit consists in beam calibration check. Each clinically used beam must undergo it at least once per two years. During 1997 e 2013, a total of 1435 beams have been thus controlled. Advanced versions of TLD audit focused on more complex conditions of irradiation (non-reference geometries, MLC fields, small IMRT fields, inhomogeneities) have been performed in the case of a request or research studies. On-site audit is performed after the commissioning of each unit. The absorbed dose to water (or RAKR for brachytherapy), beam quality, output and wedge factors, PDD, MLC positioning, MLC transmission, and dosimetric leaf gap (where applicable) are controlled. Mechanical parameters (isocenter stability, radiation field size, table parameters, etc.) are evaluated as well. A number of 535 megavoltage photon and electron external beams,103 kilovoltage external beams, and 32 brachytherapy sources have been controlled since 1996. 2 proton beams were checked in 2013. Checks of non-dosimetric parameters and imaging functions of TPS with QUASAR phantoms can be performed on request. In addition, 19 departments (23 treatment plans) have been checked using a special pelvic phantom in end-to-end audit for IMRT and IMAT prostate treatment in 2013. Delivered doses to PTV and rectum were measured with ionisation chambers in 3 planes. Planar dose distribution has been verified with EBT2 film. Retrospectively, it was possible to make DVHs analysis and compare all IMRT plans for the pelvic phantom showing common planning practice in the Czech Republic for photon IMRT and proton radiotherapy. Conclusion: The audits revealed several significant errors that might potentially lead to an accident. All results can be analysed retrospectively, showing trends related to chosen indicators. DOSIMETRY AUDITS IN RADIOTHERAPY IN GREECE C.J. Hourdakis, A. Boziari, V. Kamenopoulou. Greek Atomic Energy