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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• Use of chamber with outdated calibration factor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
30
35
40
1 2 3 4 5 6 7 8 9 10 11 12
Centres
% o
f m
ea
sure
me
nt
po
ints
exc
ee
din
g
ag
ree
me
nt
crite
ria
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.