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 20Â±5 minutes. The difference (Î”) was calculated by comparing daily measurements against the baseline measurements. The Î” in dose output was within Â±1% except in 1 case (Î”=1.5%). The Î” in radiation and imaging coincidence (X and Y directions) was within Â±1 mm except in 1 case (Î”=1.3 mm). For spot parameters, the Î” in spots positions (X & Y) was within Â±1 mm, whereas the Î” in spots sigma (X & Y) was within Â±10% for all energies. The Î” in spots skewness (X & Y) was within Â±0.5. For energy parameters, the Î” in distal & proximal ranges (R80) was within Â±0.5 mm and the Î” in distal fall-off and width were within Â±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.