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Selection of gamma analysis acceptance criteria in IMRT QA using Gafchromic EBT3 film dosimetry

  • Muhammad Isa Khan (a1), Muhammad Shakil (a1), Muhammad Bilal Tahir (a1), Muhammad Rafique (a1), Tahir Iqbal (a1), Aliza Zahoor (a1) (a2), Jalil ur Rehman (a3), Khalid Iqbal (a2) and James C. L. Chow (a4) (a5)...


Background and purpose

This study reported the justification and selection of acceptable γ criteria with respect to low (6 MV) and high (15 MV) photon beams for intensity-modulated radiation therapy quality assurance (IMRT QA) using the Gafchromic external beam therapy 3 (EBT3) film.

Materials and methods

Five-field step-and-shoot IMRT was used to treat 16 brain IMRT patients using the dual-energy DHX-S linear accelerator (Varian Medical System, Palo Alto, CA, USA). Dose comparisons between computed values of the treatment planning system (TPS) and Gafchromic EBT3 film were evaluated based on γ analysis using the Film QA Pro software. The dose distribution was analysed with gamma area histograms (GAHs) generated using different γ criteria (3%/2 mm, 3%/3 mm and 5%/3 mm) for the 6 and 15 MV photon beams, to optimise the best distance-to-agreement (DTA) criteria with respect to the beam energy.


From the comparison between the dose distributions acquired from the TPS and EBT3 film, a DTA criterion of 3%/2 mm showed less dose differences (DDs) with passing rates up to 93% for the 6 MV photon beams, while for the 15 MV a relaxed DTA criterion of 5%/3 mm was consistent with the DD acceptability criteria with a 95% passing rate.


Our results suggested that high-energy photon beams required relaxed DTA criteria for the brain IMRT QA, while low-energy photon beams showed better results even with tight DTA criteria.


Corresponding author

Author for correspondence: James Chow, Radiation Medicine Program, UHN, 700 University Avenue, ON, Toronto, Canada M5G 1Z5. Tel: 416 946 4501. Fax: 416 946 6566. E-mail:


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Cite this article: Isa Khan M, Shakil M, Tahir MB, Rafique M, Iqbal T, Zahoor A, Rehman Ju, Iqbal K, Chow JCL. (2019) Selection of gamma analysis acceptance criteria in IMRT QA using Gafchromic EBT3 film dosimetry. Journal of Radiotherapy in Practice18: 127–131. doi: 10.1017/S1460396918000602



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