title: Monte Carlo study of the potential reduction in out-of-field dose using a patient-specific aperture in pencil beam scanning proton therapy.
abstract: This study is aimed at identifying the potential benefits of using a patient-specific aperture in proton beam scanning. For this purpose, an accurate Monte Carlo model of the pencil beam scanning (PBS) proton therapy (PT) treatment head at Massachusetts General Hospital (MGH) was developed based on an existing model of the passive double-scattering (DS) system. The Monte Carlo code specifies the treatment head at MGH with sub-millimeter accuracy. The code was configured based on the results of experimental measurements performed at MGH. This model was then used to compare out-of-field doses in simulated DS treatments and PBS treatments. For the conditions explored, the penumbra in PBS is wider than in DS, leading to higher absorbed doses and equivalent doses adjacent to the primary field edge. For lateral distances greater than 10 cm from the field edge, the doses in PBS appear to be lower than those observed for DS. We found that placing a patient-specific aperture at nozzle exit during PBS treatments can potentially reduce doses lateral to the primary radiation field by over an order of magnitude. In conclusion, using a patient-specific aperture has the potential to further improve the normal tissue sparing capabilities of PBS.
authors.affiliation: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia. dowdell@partners.org
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Dowdell
authors.forename: Benjamin
authors.initials: B
authors.lastname: Clasie
authors.forename: Nicolas
authors.initials: N
authors.lastname: Depauw
authors.forename: Peter
authors.initials: P
authors.lastname: Metcalfe
authors.forename: Anatoly B
authors.initials: AB
authors.lastname: Rosenfeld
authors.forename: Hanne M
authors.initials: HM
authors.lastname: Kooy
authors.forename: Jacob B
authors.initials: JB
authors.lastname: Flanz
authors.forename: Harald
authors.initials: H
authors.lastname: Paganetti
mesh_terms: D006801:Humans; D008297:Male; D009010:Monte Carlo Method; D057285:Precision Medicine / Q000379:methods*; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D061766:Proton Therapy; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D011522:Protons
chemical_list: D011522:Protons