S Bhagroo*, K Hopfensperger, R Price, J Kunz, F Su, G Nelson, A Paxton, University of Utah, Salt Lake City, UT

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  S Bhagroo

PO-GePV-T-326 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Varian TrueBeam (Varian Medical Systems, Palo Alto, CA) linacs are commonly employed at clinics worldwide. Currently, there is no standard set of reference beam data for 18 MV photons. In this work, we have assembled 18 MV beam data from the commissioning of 6 linacs across our institution for use as a comparative resource.

Methods: A sample of 18 MV beam data from the commissioning of 5 Varian TrueBeam and 1 Varian Edge linacs is provided, mirroring those presented by Glide-Hurst et al. (2013). Profiles and PDDs were obtained with an SNC (Sun Nuclear Corporation, Melbourne, FL) 3D Scanner water tank and an SNC125c ion chamber. Output factors were obtained with an IBA (IBA Dosimetry, Herndon, VA) cc13 ion chamber at 90 cm SSD at 10 cm depth in solid water. Ppol and Pion values were obtained from TG-51 measurements during commissioning for each linac. MLC transmission values were obtained for 10x20 cm² and 10x10 cm² fields for standard (SD) MLCs (4 TrueBeams) and HD MLCs (1 Edge and 1 TrueBeam), respectively.

Results: Mean values for Ppol and Pion were 0.9978+0.0012, and 1.0035+0.0005, respectively. PDDs at 5/10/20 cm depths varied by less than 0.12% across all 6 linacs for a 10x10 cm² field. Mean penumbra (cross-plane) for a 10x10 cm² field at 10 cm depth was 8.13+0.33 mm (range: 0.74-0.838 mm) for all linacs, and output factors at field sizes of 5/20/30/40 cm² varied by less than 0.74% across 4 linacs. Mean transmission was 1.62+0.03% (SD MLCs) and 1.20+0.02% (HD MLCs).

Conclusion: Institutional commissioning data for 18 MV photon beams for all 6 of our Varian TrueBeam and Edge linacs demonstrates good agreement for output, profiles, and MLC transmission. These data could be used as a reference for those wishing to match other 18 MV data to these values.

Keywords

Commissioning, Linear Accelerator, Radiation Therapy

Taxonomy

TH- External Beam- Photons: General (most aspects)

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