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Proton Beam Stability of ProteusPLUS PBS Proton System: Our Initial Clinical Experience

S Rana*, L Coutinho , A Gutierrez , J Bennouna , M Leyva , V Chirinos , W Hsi , Miami Cancer Institute, Miami, FL


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: The purpose of this study is to report our initial experience on the stability of a ProteusPLUS pencil beam scanning (PBS) proton therapy system at our center.

Methods: The beam stability is tested using a single couch top setup with the Sphinx, Lynx, and parallel-plate ion chamber on a daily basis. A PBS proton treatment plan was developed to evaluate variations in dose output, radiation and imaging coincidence, spot parameters (position, size, and skewness) for 4 energies (106 MeV, 145 MeV, 172 MeV & 221 MeV), and energy parameters (distal and proximal ranges, distal fall-off, and width) for the same 4 energies used as in spot parameters.

Results: The results presented are based on 80 sets of measurements from the past ~4 months. Average time for setup, acquisition, and data analysis was 20±5 minutes. The difference (Δ) was calculated by comparing daily measurements against the baseline measurements. The Δ in dose output was within ±1% except in 1 case (Δ=1.5%). The Δ in radiation and imaging coincidence (X and Y directions) was within ±1 mm except in 1 case (Δ=1.3 mm). For spot parameters, the Δ in spots positions (X & Y) was within ±1 mm, whereas the Δ in spots sigma (X & Y) was within ±10% for all energies. The Δ in spots skewness (X & Y) was within ±0.5. For energy parameters, the Δ in distal & proximal ranges (R80) was within ±0.5 mm and the Δ in distal fall-off and width were within ±0.3 mm.

Conclusion: Our initial experience based on 80 daily measurements showed good stability of the ProteusPLUS PBS proton therapy system. The use of the Sphinx in conjunction with the Lynx and a parallel-plate ion chamber was shown to provide a robust and efficient method of evaluating PBS proton beam parameters.


Quality Assurance, Protons, Dosimetry


TH- External Beam- Particle therapy: Proton therapy - quality assurance

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