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Session: Advancing Science to Expand Access to State-of-the-Art Applications in Medical Physics: II [Return to Session]

Practical Consideration of Single-Energy Bragg Peak FLASH-RT for Lung Tumor Treatment Planning

M Kang*, S Wei, JI Choi, CB Simone, II, H Lin, New York Proton Center, New York, NY

Presentations

TU-F115-IePD-F5-5 (Tuesday, 7/12/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 5

Purpose: To investigate practical aspects of a novel Bragg peak FLASH-RT technique, including spot dose-rate evolution, dose and dose-rate calculation accuracy, and plan robustness, for clinical application in lung cancer treatment.

Methods: The inverse treatment optimization synergy with proton range pull-back and compensation can achieve tumor distal tracking using single-energy Bragg peak while still preserving FLASH dose-rate delivery. The multiple Coulomb scattering (MCS) between protons and universal range shifter (URS) and range compensator (RC) can enlarge beam divergence causing the spot-peak-dose-rate to decrease significantly. A fast Monte Carlo (MC) tool, MCsquare, was also commissioned to compare the proton convolution superposition(PCS) dose and dose-rate calculation. A clinical robustness evaluation method (±5mm setup errors and ± 3.5% range uncertainties) was performed to assess the dosimetric impact of setup errors and CT calibration uncertainties for Bragg peak planning.

Results: Spot dose-rate decreased when the air gap increased, and the central axis dose-rate at the Bragg peak was reduced by a factor of ~2 between 5cm and 25cm air gaps. The largest dose-rate difference between PCS and MC occurred at the distal part of the proton beam traveling through air-soft tissue interfaces and the field edge area or penumbra region. The dose-rate-volume-histogram(DRVH) decreased using the MC method but still maintained acceptable V40Gy/s coverage for all OARs. The D95 second worst-case scenario for iCTV decreased from 95% to 92.7%(±2.7%), and median D95 was 96.3%(±1.9%) when range and setup uncertainties were present.

Conclusion: Minimizing the air gap is essential in maintaining proton fluence intensity and a smaller penumbra, which is crucial for OAR sparing. MC is recommended for FLASH dose and dose-rate calculation in lung tumor treatment planning. The robustness analysis demonstrated that novel Bragg peak planning can maintain excellent coverage when incorporating clinical setup and range uncertainties.

Keywords

Protons, Pencil Beam Algorithms, Monte Carlo

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – Development (new technology and techniques)

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