1. Results of IAEA supported TPS audit in Europe
Eduard Gershkevitsh
North Estonia Medical Center
Tallinn, Estonia

2. 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

3. 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

4. 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

5. 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

6. Participants of the TPS Audit
8 countries
61 centres
195 datasets (combination of algorithms and beam quality)

7. 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)

8. Reasons for deviations
Dosimetry problems
Discrepancies requiring intervention and not related to algorithm limitations were found in approximately 9% of datasets
Reasons for deviations

9. Calibration Use of chamber with outdated calibration factor
Use of plastic phantom instead of water for calibration
Incorrect value in TPS

10. Input beam data & model fitting
Typographic errors
Use of standard data
Quality of measurement data
Sub-optimal beam fitting

11. Problems with model beam fitting

12. Problems with treatment unit
New couch top was installed and unaccounted. This lead to 8% underdose from posterior fields
Loose mechanical wedge

13. Accuracy achievable
With corrected data and advanced algorithms the majority of the measurements are within agreement criteria

14. 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

15. 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

16. 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 May;53(5):