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Beam Data Comparison for 20 Linear Accelerators in One Network

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T LoSasso

T LoSasso*, S Lim , G Tang , M Chan , J Li , C Obcemea , Y Song , R Ma , G Yang , W Xiong , D Huang , C Burman , J Mechalakos , M Hunt , Memorial Sloan-Kettering Cancer Center, New York, NY


SU-E-T-52 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To compare photon beam data for the 20 Varian linear accelerators (TrueBeam, iX, and EX models) in use at five centers in the same network with the intent to model with one set of beam data in Eclipse.

Methods: Varian linear accelerators, TrueBeam (3), 21 EX, iX, and Trilogy (14), and 6 EX (3), installed between 1999 and 2014 have their 6 MV and 15 MV x-ray beams reevaluated. Full commissioning, including output factors (St), percent depth doses (PDD), and off-axis profiles, was recently performed for a TrueBeam with a cc04 ion chamber in an IBA Blue phantom. Similarly, a subset of beam data for each of the other accelerators was measured recently as follows: for 3x3, 10x10, and 30x30 cm² field sizes, flatness and penumbra (80-20%) were measured at dmax and 10 cm depths, PDD were measured at 10 and 20 cm depths, and St were measured at 5 cm depth. Measurement results for all machines were compared.

Results: For 15 high-energy (6 and 15 MV) and 3 low-energy machines (6MV only): 1) PDD agreed within 1.4% at 10 and 20 cm depths; 2) penumbra agreed within 1.0 mm at dmax and 10 cm depths; 3) flatness was within 1.3% at dmax and 10 cm depths; and 4) with exception of the three low energy machines, output factors were within 1.1% and 0.5% for 3x3 and 30x30 cm², respectively. Measurement uncertainty, not quantified here, accounts for some of these differences.

Conclusion: Measured beam data from 15 high-energy Varian linacs are consistent enough that they can be classified using one beam data set in Eclipse. Two additional high-energy machines are removed from this group until their data are further confirmed. Three low-energy machines will be in a separate class based upon differences in output factors (St).

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