Results of IAEA supported TPS audit in

Europe

Eduard Gershkevitsh

North Estonia Medical Center

Tallinn, Estonia

• 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

Principles of operation

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

• 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

National TPS audit coordinators

Participants of the TPS Audit

• 8 countries

• 61 centres

• 195 datasets (combination of algorithms and beam quality)

• 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)

CT to RED conversion

• Discrepancies requiring intervention and not related to algorithm limitations were found in approximately 9% of datasets

Reasons for deviations

Calibration39%

Input beam data and model fitting

50%

Mech. problems 11%

Dosimetry problems

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• Use of chamber with outdated calibration factor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

0

5

10

15

20

25

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40

1 2 3 4 5 6 7 8 9 10 11 12

Centres

% o

f m

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4-6MV Varian HE

10-18MV Varian HE

Problems with model beam fitting

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.