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Patient Specific Quality Assurance of Volumetric Modulated Arc Therapy (VMAT): Portal Dosimetry Compared with ArcCheck Phantom

K Utitsarn*, T Watthanasarn, J Pimthong, K Krongkietlearts, C Pihusut, W Chaloemchawalit, J Jitmon, S Khuanchana, Lopburi Cancer Hospital, Lopburi, Thailand


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: compare the result of Portal Dosimetry system (PDs) with ArcCheck for delivery quality assurance of head and neck and prostate Volumetric Modulated Arc Therapy (VMAT) with various gamma criteria evaluation.

Methods: Varian amorphous silicon (aSi) Portal Imaging Devices and its software was used for portal dosimetry. A 3D array ArcCheck cylindrical was used for phantom studies. Eclipse-TPS with VMAT treatment planning and portal dose prediction software was used for planar dose calculations. The 40 VMAT patient plans of head and neck site and prostate site from department of radiotherapy, Lopburi Cancer Hospital were created for verification plan on two different QA system PDs and ArcCheck. Fourty plans each with 3 arcs were delivered on the EPIDs of the Varian Linac iX and on ArcCheck cylindrical phantom respectively. The measured planar dose matrices were compared with planned dose and were analysed using global gamma evaluation with the criteria of 3% dose difference and 3mm distance to agreement and 3% dose difference and 2mm distance to agreement.

Results: VMAT plans passed the 3%/3mm gamma criteria by more than 95 % on both dosimetry system. The average passing rate for head and neck region is 98.2% and 97.6% for PDs and Arccheck and the average passing rate for prostate region is 99.0% and 98.6%, respectively. The gamma passing rate were decreased when reduce the gamma criteria to 3%/2mm. The average passing rate of 96.7% and 95.1% was found for head and neck region and 96.9 and 97.2 was found for prostate region. Similarly, the mean deviations and SD values are less in portal dosimetry than that of Arccheck.

Conclusion: PDs system and Arccheck can be considered as a QA tools for the verification plan of VMAT. The results of planning verification were comparable.


Not Applicable / None Entered.


TH- Radiation Dose Measurement Devices: EPID/portal dosimetry

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