Results of IAEA supported TPS audit in Europe Eduard Gershkevitsh North Estonia Medical Center Tallinn, Estonia Principles of operation • TPS audit uses IAEA TECDOC 1583 methodology • IAEA provides CIRS Thorax phantom on loan for 6 month to the Member State • IAEA together with national audit coordinator (Medical Physics group, RT department nominated by the national authorities) organise one day workshop in the country • National audit coordinator’s centre is audited by independent auditor • National audit coordinator is performing audits through on site visits IAEA TECDOC 1583 methodology • Based on anthropomorphic phantom • To verify that logistic chain: CT scanning Treatment planning Data transfer Dose delivery is operational and leads to desired results with sufficient accuracy • Employs ionisation chamber measurements IAEA TECDOC 1583 methodology • Eight test cases with 15 measurement points Single 10x10cm2 field at nominal SSD Tangential field with wedge Corner blocks 4-field “box” Customised blocking Oblique incidence with L-shape block Half fields with wedges Non-coplanar field arrangement • Agreement criteria 2-5% depending on complexity National TPS audit coordinators • B. Petrovic – Institute of Oncology Vojvodina, Sremska Kamenica, Serbia • C. Pesznyak – National Institute of Oncology, Budapest, Hungary • K. Chelminski – M. Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland • J. Grezdo – St. Elizabeth Institute of Oncology, Bratislava, Slovakia • M. do Carmo Lopes – Portuguese Institute of Oncology, Coimbra, Portugal • E. Gershkevitsh – North Estonia Medical Centre, Tallinn, Estonia Participants of the TPS Audit • 8 countries • 61 centres • 195 datasets (combination of algorithms and beam quality) CT to RED conversion • CT to RED conversion curve required adjustment in 2/3 of centres (criteria used adopted from IAEA TRS 430 – for the same electron density the variation should not exceed ± 20HU for all materials except water (± 5HU) Dosimetry problems • Discrepancies requiring intervention and not related to algorithm limitations were found in approximately 9% of datasets Reasons for deviations Mech. problems 11% Input beam data and model fitting 50% Calibration 39% Calibration • Use of chamber with outdated calibration factor • Use of plastic phantom instead of water for calibration • Incorrect value in TPS Input beam data & model fitting • Typographic errors • Use of standard data • Quality of measurement data • Sub-optimal beam fitting % of measurement points exceeding agreement criteria Problems with model beam fitting 4-6MV Varian HE 10-18MV Varian HE 40 35 30 25 20 15 10 5 0 1 2 3 4 5 6 Centres 7 8 9 10 11 12 Problems with treatment unit • New couch top was installed and unaccounted. This lead to 8% underdose from posterior fields • Loose mechanical wedge Accuracy achievable • With corrected data and advanced algorithms the majority of the measurements are within agreement criteria Conclusion • Input beam data and suboptimal beam modelling were the largest contributors to observed deviations • CT to RED conversion is customised in minority of centres • The majority of observed deviations have been corrected • Contribution to better understanding of TPS performance and its limitations Acknowledgement • Stanislav Vatnitsky for drafting a proposal for TPS audit • Joanna Izewska for support and implementation of the TPS audit at IAEA • To national audit coordinators • To medical physicist at audited RT departments Thank you for attention! More details: Gershkevitsh E, Pesznyak C, Petrovic B, Grezdo J, Chelminski K, do Carmo Lopes M, Izewska J, Van Dyk J. Dosimetric inter-institutional comparison in European radiotherapy centres: Results of IAEA supported treatment planning system audit. Acta Oncol. 2014 May;53(5):628-36.