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On-Site Beam Matching of An Elekta Infinity with Agility MLC with An Elekta Versa HD

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C Nelson

C Nelson*, M Garcia , B Mason , S Kirsner , UT M.D. Anderson Cancer Center, Houston, TX


SU-F-T-487 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:Historically, beam matching of similar Linear Accelerators has been accomplished by sending beam data to the manufacturer to match at their factory. The purpose of this work is to demonstrate that fine beam matching can be carried out on-site as part of the acceptance test, with similar or better results.

Methods: Initial scans of a 10 x 10 Percent depth dose (PDD) and a 40 x 40 beam profile at the depth of Dmax, for 6MV and 10 MV were taken to compare with the standard beam data from the Versa. The energy was then adjusted and the beam steered to achieve agreement between the depth dose and the horns of the beam profile. This process was repeated until the best agreement between PDD and profiles was achieved. Upon completion, all other clinical data were measured to verify match. This included PDD, beam profiles, output factors and Wedge factors. For electron beams PDD’s were matched and the beam profiles verified for the final beam energy. Confirmatory PDD and beam profiles for clinical field sizes, as well as Output Factors were measured.

Results:The average difference in PDD’s for 6MV and 10MV were within 0.4% for both wedged and open fields. Beam profile comparisons over the central 80% of the field, at multiple depths, show agreement of 0.8% or less for both wedged and open fields. Average output factor agreement over all field sizes was 0.4% for 6MV and 0.2 % for 10MV. Wedge factors agreement was less than 0.6% for both photon energies over all field sizes. Electron PDD agreed to 0.5mm. Cone ratios agreed to 1% or less.

Conclusion:This work indicates that beam matching can be carried out on-site simply and quickly. The results of this beam matching can achieve similar or better results than factory matching.

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