A Rodrigues*, E Cullom, Y Xie, Y Sheng, J Kowalski, Q Wu, Duke University Medical Center, Durham, NC

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  A Rodrigues

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SU-H430-IePD-F4-2 (Sunday, 7/10/2022) 4:30 PM - 5:00 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 4

Purpose: To present the reproducibility and consistency of commissioning for a standing and recumbent Total Skin Electron Therapy (TSET) technique between a Varian TrueBeam STx (TBSTx) and TrueBeam (TB) linac and provide updated guidance to institutions implementing TSET.

Methods: Acceptance and commissioning data were analyzed for a TBSTx and TB for a standing Stanford technique (2013(TBSTx), 2022(TB)) and for a recumbent technique (2018(TBSTx), 2022(TB)) using 6HDTSE energy. Tasks included acceptance of the basic dosimetry and establishment of technique geometry. Measurements included profiles and PDDs at reference and treatment conditions, relative output factors, photon contamination, and ozone production measurements and calculations. Solid water and phantom measurements (rectangular, cylindrical, anthropomorphic) were taken with parallel-plate and cylindrical ionization chambers, film, and TLDs/OSLDs. End-to-end testing with an anthropomorphic phantom was conducted. Comparison to Monte Carlo simulations was also done.

Results: The same treatment geometry were validated: SSDs (standing: 300 cm, recumbent: 195, 305 cm (vertex, oblique fields)), deflecting angles (standing: ±19°; recumbent: 0°, ±60° (vertex); + or -60° (oblique)). The recumbent technique utilizes a Cu filter. PDDs and profiles at 100 cm SSD agreed well (dmax = 1.3 cm). At treatment condition, PDDs agreed within 1% (standing) and 3% (recumbent). dmax agreed within 0.2 cm (standing, recumbent). R50 (cm) agreed within 0.2 cm (standing, recumbent). Photon contamination at CAX was <1% (standing) and <3% (recumbent). Profiles agreed within 1% (standing) and 2.5% (recumbent). B-factors were 3.44 (TB) vs 3.40 (TBSTx) (standing) and 3.91 (TB) vs 3.64 (TBSTx) (recumbent). Output factor agreed <1% (standing) and <2% (recumbent). End-to-end testing yielded similar
results: CAX was <5% and all sites were <10% except for expected under/overdosing areas. Ozone production was <0.1 ppm and well under the limit.

Conclusion: Good agreement was observed and end-to-end testing resulted in comparable dosimetry for each techniques on both linacs.

Keywords

Total Skin Irradiation, Electron Therapy, Commissioning

Taxonomy

TH- External Beam- Electrons: Development (new technology and techniques)

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