title: Technical Note: A treatment plan comparison between dynamic collimation and a fixed aperture during spot scanning proton therapy for brain treatment.
abstract: OBJECTIVE
  To quantitatively assess the advantages of energy-layer specific dynamic collimation system (DCS) versus a per-field fixed aperture for spot scanning proton therapy (SSPT).
  
  
  METHODS
  Five brain cancer patients previously planned and treated with SSPT were replanned using an in-house treatment planning system capable of modeling collimated and uncollimated proton beamlets. The uncollimated plans, which served as a baseline for comparison, reproduced the target coverage and organ-at-risk sparing of the clinically delivered plans. The collimator opening for the fixed aperture-based plans was determined from the combined cross sections of the target in the beam's eye view over all energy layers which included an additional margin equivalent to the maximum beamlet displacement for the respective energy of that energy layer. The DCS-based plans were created by selecting appropriate collimator positions for each row of beam spots during a Raster-style scanning pattern which were optimized to maximize the dose contributions to the target and limited the dose delivered to adjacent normal tissue.
  
  
  RESULTS
  The reduction of mean dose to normal tissue adjacent to the target, as defined by a 10 mm ring surrounding the target, averaged 13.65% (range: 11.8%-16.9%) and 5.18% (2.9%-7.1%) for the DCS and fixed aperture plans, respectively. The conformity index, as defined by the ratio of the volume of the 50% isodose line to the target volume, yielded an average improvement of 21.35% (19.4%-22.6%) and 8.38% (4.7%-12.0%) for the DCS and fixed aperture plans, respectively.
  
  
  CONCLUSIONS
  The ability of the DCS to provide collimation to each energy layer yielded better conformity in comparison to fixed aperture plans.
authors.affiliation: Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
authors.forename: Blake
authors.initials: B
authors.lastname: Smith
authors.affiliation: Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
authors.forename: Edgar
authors.initials: E
authors.lastname: Gelover
authors.affiliation: Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Moignier
authors.affiliation: Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
authors.forename: Dongxu
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
authors.forename: Ryan T
authors.initials: RT
authors.lastname: Flynn
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, TRC 2 West, 3400 Civic Center Boulevard, Philadelphia, Pennsylvania 19104.
authors.forename: Liyong
authors.initials: L
authors.lastname: Lin
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, TRC 2 West, 3400 Civic Center Boulevard, Philadelphia, Pennsylvania 19104.
authors.forename: Maura
authors.initials: M
authors.lastname: Kirk
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, TRC 2 West, 3400 Civic Center Boulevard, Philadelphia, Pennsylvania 19104.
authors.forename: Tim
authors.initials: T
authors.lastname: Solberg
authors.affiliation: Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, Iowa 52242.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Hyer
mesh_terms: D001932:Brain Neoplasms / Q000532:radiotherapy*; D006801:Humans; D061766:Proton Therapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*