Highlights
- •Validation of EPID pre-treatment & transit dose using 2D and 3D detectors.
- •Direct comparison between EPID pre-treatment, transit, 2D/3D detectors.
- •Validation indicates achievable gamma index under ideal conditions.
- •In-house gamma methodology ensures consistency for 2D and 3D modalities.
Abstract
Purpose
To provide a 3D dosimetric evaluation of a commercial portal dosimetry system using
2D/3D detectors under ideal conditions using VMAT.
Methods
A 2D ion chamber array, radiochromic film and gel dosimeter were utilised to provide
a dosimetric evaluation of transit phantom and pre-treatment ‘fluence’ EPID back-projected
dose distributions for a standard VMAT plan. In-house 2D and 3D gamma methods compared
pass statistics relative to each dosimeter and TPS dose distributions.
Results
Fluence mode and transit EPID dose distributions back-projected onto phantom geometry
produced 2D gamma pass rates in excess of 97% relative to other tested detectors and
exported TPS dose planes when a 3%, 3 mm global gamma criterion was applied. Use of
a gel dosimeter within a glass vial allowed comparison of measured 3D dose distributions
versus EPID 3D dose and TPS calculated distributions. 3D gamma comparisons between
modalities at 3%, 3 mm gave pass rates in excess of 92%. Use of fluence mode was indicative
of transit results under ideal conditions with slightly reduced dose definition.
Conclusions
3D EPID back projected dose distributions were validated against detectors in both
2D and 3D. Cross validation of transit dose delivered to a patient is limited due
to reasons of practicality and the tests presented are recommended as a guideline
for 3D EPID dosimetry commissioning; allowing direct comparison between detector,
TPS, fluence and transit modes. The results indicate achievable gamma scores for a
complex VMAT plan in a homogenous phantom geometry and contributes to growing experience
of 3D EPID dosimetry.
Keywords
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References
- 3D EPID-based in vivo dosimetry for IMRT and VMAT.J Phys Conf Ser. 2013; 444: 012011
- A literature review of electronic portal imaging for radiotherapy dosimetry.Radiother Oncol. 2008; 88: 289-309
- Comparison of ghosting effects for three commercial a-Si EPIDs.Med Phys. 2006; 33: 2448-2451
- Electronic portal imaging devices: a review and historical perspective of contemporary technologies and research.Phys Med Biol. 2002; 47: R31-R65
- A real-time, flatpanel, amorphous silicon, digital X-ray imager.Radiographics. 1995; 15: 993-1000
- Dosimetric properties of an amorphous silicon electronic portal imaging device for verification of dynamic intensity modulated radiation therapy.Med Phys. 2003; 30: 1618-1627
- The use of an aSi-based EPID for routine absolute dosimetric pre-treatment verification of dynamic IMRT fields.Radiother Oncol. 2004; 71: 223-234
- Verification of treatment parameter transfer by means of electronic portal dosimetry.Med Phys. 2004; 31: 341-347
- A dose delivery verification method for conventional and intensity-modulated radiation therapy using measured field fluence distributions.Med Phys. 2003; 30: 2996-3005
- 3D dose reconstruction to ensure correct external beam treatment of patients.Med Dosim. 2007; 32: 157-165
- A simple backprojection algorithm for 3D in vivo EPID dosimetry of IMRT treatments.Med Phys. 2009; 36: 3310-3321
- A method for deconvolution of integrated electronic portal images to obtain incident fluence for dose reconstruction.J Appl Clin Med Phys. 2005; 6: 22-39
- 3D EPID-based in vivo dosimetry: a major step forward towards optimal quality and safety in radiation oncology practice.Med Phys. 2014; 41: 457
- Current status of 3D EPID-based in vivo dosimetry in The Netherlands Cancer Institute.J Phys Conf Ser. 2015; 573: 012014
- Quasi 3D dosimetry (EPID, conventional 2D/3D detector matrices).J Phys: Conf Ser. 2015; 573
- Implementation and evaluation of a transit dosimetry system for treatment verification.Phys Med. 2016; 32: 671-680
- On using 3D γ-analysis for IMRT and VMAT pretreatment plan QA.Med Phys. 2012; 39: 3051-3059
- Evaluation of Dosimetry Check software for IMRT patient-specific quality assurance.J Appl Clin Med Phys. 2015; 16: 5427
- Is a quasi-3D dosimeter better than a 2D dosimeter for Tomotherapy delivery quality assurance?.J Phys Conf Ser. 2015; 573: 012077
- Correlation analysis between 2D and quasi-3D gamma evaluations for both intensity-modulated radiation therapy and volumetric modulated arc therapy.Oncotarget. 2017; 8: 5449-5459
- Commissioning and initial experience with a commercial software for in vivo volumetric dosimetry.Physica Med. 2014; 30: 954-959
Alber M, Broggi S, De Wagter C et al. Guidelines for the verification of IMRT. ESTRO Booklet no. 9. 1st ed. Brussels, Belgium, ESTRO; 2008.
- Dosimetric IMRT verification with a flat-panel EPID.Med Phys. 2003; 30: 3143-3155
- Dosimetric characterization and use of GAFCHROMIC EBT3 film for IMRT dose verification.J Appl Clin Med Phys. 2013; 14
- Evaluation of a 2D detector array for patient-specific VMAT QA with different setups.Phys Med Biol. 2011; 56: 7163-7177
- Angular dose dependence of Matrixx TM and its calibration.J Appl Clin Med Phys. 2010; 11: 3057
- Radiochromic film dosimetry: recommendations of AAPM radiation therapy committee task group 55.Med Phys. 1998; 25: 2093-2115
- Multichannel film dosimetry with non-uniformity correction.Med Phys. 2011; 38: 2523-2534
- Evaluation of a novel triple-channel radiochromic film analysis procedure using EBT2.Phys Med Biol. 2012; 57: 4353-4368
- Influence of preparation and calibration method of PAGAT dosimeter on TSE MR readout results.J Phys Conf Ser. 2013; 444: 012093
- Validation of MR-based polymer gel dosimetry as a preclinical three-dimensional verification tool in conformal radiotherapy.J Magn Reson Imaging. 2000; 43: 116-125
- Challenges in calculation of the gamma index in radiotherapy – Towards good practice.Physica Med. 2017; 36: 1-11
- A technique for the quantitative evaluation of dose distributions.Med Phys. 1998; 25
- Comparison of 2D and 3D gamma analyses.Med Phys. 2014; 41: 021710
- Comparison of 2D and 3D Gamma calculations for an IMRT QA phantom.J Phys: Conf Ser. 2015; 573 (012055)
- In vivo dosimetry in UK external beam radiotherapy: current and future usage.Br J Radiol. 2017; 90: 20160915
Article info
Publication history
Accepted:
November 19,
2017
Received in revised form:
October 5,
2017
Received:
May 3,
2017
Identification
Copyright
© 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
