M Chen, J Tan, G Gibbard, Y Park, T Zhuang, M Lin, K Wang, X Jia, B Cai, W Lu*, University of Texas Southwestern Medical Center, Dallas, TX

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  M Chen

TU-D1030-IePD-F7-4 (Tuesday, 7/12/2022) 10:30 AM - 11:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: The RefleXion® X1 is a novel radiotherapy system with a 6 MV LINAC and onboard CT and PET imaging, which may one day be used for biology-guided radiation therapy. Accurate and independent modeling of X1 LINAC radiation beam is essential for its quality assurance. We propose an independent beam model for the X1 using parameters derived from measurements.

Methods: We decomposed beam modeling into two independent components, fluence map and energy spectrum, and utilized two sets of parameters to model the fluence map: the open field and individual T&G leaf filters. Both the fluence map and energy spectrum were tuned to minimize difference between dose calculated by an in-house general-purpose Monte Carlo (MC) dose engine and measurements based on a set of water tank beam scanning data acquired at SSD=85cm setup. For each jaw width (1cm-2cm), we measured the depth dose, crossline, and inline profiles at multiple depths (1.5cm-10cm-20cm) for central-leaf openings (2-4-8-16-32-64). We used the small fields (2.5cm×1cm-2.5cm×2cm) to tune the energy spectrum and the largest fields (40cm×1cm-40cm×2cm) to tune the fluence map. The in-air crossline profiles of 2cm jaw width for single and dual leaf openings were also acquired to tune the leaf filters that account for sequential T&G effects. All other measurements were used for verification.

Results: MC-dose of the tuned beam model matched well with measurements in terms of beam quality index (PDD10 of 10cm×1cm field, calculation-vs-measurements, 54.66%-vs-54.56%), inline-FWHM of 10cm×1cm (1.13cm-vs-1.10cm), crossline-FWHM of both 10cm×1cm and 10cm×2cm (11.01cm-vs-11.03cm), difference of FWHM for all fields (inline: 0.02cm±0.04cm; crossline: 0.03cm±0.00cm), and output factors (1.25cm×1cm: 0.8542-vs-0.8577; 40cm×2cm: 1.0134-vs-1.0138) normalized (OF=1) by 10cm×2cm at 10cm depth.

Conclusion: The proposed beam modeling was derived purely from measurements without assumptions for the LINAC head configuration or phase-space generation and can be used to provide independent verification for X1 LINAC beam.

Funding Support, Disclosures, and Conflict of Interest: RefleXion Master Research Agreement

Keywords

Dose

Taxonomy

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

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