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Validation of Vendor-Provided Beam Model for a Novel Flattening Filter Free (FFF) Straight Through Linac with Prototype Fast Jawless MLC Collimation

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S Anamalayil

S Anamalayil*, R Scheuermann , C Kennedy , D Mihailidis , L Dong , J Metz , University of Pennsylvania, Philadelphia, PA


SU-I-GPD-T-429 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To compare and validate the vendor-provided model of a novel flattening filter-free (FFF) straight-through Linac with prototype fast jawless MLC collimation. This study outlines the comparison and validation of the beam model provided by the vendor for this prototype system.

Methods: Beam data acquisitions were performed based on TG-106 guidelines, for a 6X-FFF photon beam with a prototype jawless MLC collimation system. Percentage depth doses, in-plane & cross-plane profiles and output factors were acquired for many square field sizes varying from 2x2cm to 28x28cm at different depths. IBA Blue phantom, IBA CC04, CC13 chambers and Scanditronix Diode detectors were used to accommodate measurements for small and large filed sizes and penumbra region. MLC transmission values and dosimetric leaf gap (DLG) values were measured. As a part of the validation process TG-119 ion chamber measurements in solid water for all five recommended plans for both IMRT and VMAT techniques, were performed. Arc-check was used for IMRT/VMAT QA validation measurements.

Results: The measured profiles and the percentage depth doses were in agreement except the PDDs for small field sizes up to 6x6cm, which showed shallower PDDs with a difference of less than 1% from the vendor-provided data. The output measurements were less than 0.5% from the vendor-provided values. Measured MLC transmission values and DLG values were also less than 0.5% from the vendor provided values. TG-119 measurements were within 2% for all plans except easy/hard shaped targets which simulated spine SBRT. The easy/hard shaped plan measurements varied between -4.3% and +2.0%. The calculated confidence interval for VMAT was above the average value reported in TG-119 whereas that of IMRT was below. IMRT/VMAT measurements also showed very good results.

Conclusion: Overall the vendor-provided beam data agreed very well with our standard validation measurements.

Funding Support, Disclosures, and Conflict of Interest: This work was performed as part of a research agreement with Varian Medical Systems.

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