title: Proton beam scattering system optimization for clinical and research applications.
abstract: OBJECTIVE
  To develop and test a method for optimizing and constructing a dual scattering system in passively scattered proton therapy.
  
  
  METHODS
  A beam optics optimization algorithm was developed to optimize the thickness of the first scatterer (S1) and the profile (of both the high-Z material and Lexan) of the second scatterer (S2) to deliver a proton beam matching a given set of parameters, including field diameter, fluence, flatness, and symmetry. A new manufacturing process was also tested that allows the contoured second scattering foil to be created much more economically and quickly using Cerrobend casting. Two application-specific scattering systems were developed and tested using both experimental and Monte Carlo techniques to validate the optimization process described.
  
  
  RESULTS
  A scattering system was optimized and constructed to deliver large uniform irradiations of radiobiology samples at low dose rates. This system was successfully built and tested using film and ionization chambers. The system delivered a uniform radiation field of 50 cm diameter (to a dose of ± 7% of the central axis) while the depth dose profile could be tuned to match the specifications of the particular investigator using modulator wheels and range shifters. A second scattering system for intermediate field size (4 cm < diameter < 10 cm) stereotactic radiosurgery and radiation therapy (SRS and SRT) treatments was also developed and tested using GEANT4. This system improved beam efficiency by over 70% compared with existing scattering systems while maintaining field flatness and depth dose profile. In both cases the proton range uniformity across the radiation field was maintained, further indicating the accuracy of the energy loss formalism in the optimization algorithm.
  
  
  CONCLUSIONS
  The methods described allow for rapid prototyping of scattering foils to meet the demands of both research and clinical beam delivery applications in proton therapy.
authors.affiliation: Loma Linda University Medical Center, Loma Linda, California 92354, USA. awroe@dominion.llumc.edu
authors.forename: A J
authors.initials: AJ
authors.lastname: Wroe
authors.forename: R W
authors.initials: RW
authors.lastname: Schulte
authors.forename: S
authors.initials: S
authors.lastname: Barnes
authors.forename: G
authors.initials: G
authors.lastname: McAuley
authors.forename: J D
authors.initials: JD
authors.lastname: Slater
authors.forename: J M
authors.initials: JM
authors.lastname: Slater
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008962:Models, Theoretical; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation* / Q000379:methods*; D012542:Scattering, Radiation; D011522:Protons
chemical_list: D011522:Protons