title: A case study in proton pencil-beam scanning delivery.
abstract: OBJECTIVE
  We completed an implementation of pencil-beam scanning (PBS), a technology whereby a focused beam of protons, of variable intensity and energy, is scanned over a plane perpendicular to the beam axis and in depth. The aim of radiotherapy is to improve the target to healthy tissue dose differential. We illustrate how PBS achieves this aim in a patient with a bulky tumor.
  
  
  METHODS
  Our first deployment of PBS uses "broad" pencil-beams ranging from 20 to 35 mm (full-width-half-maximum) over the range interval from 32 to 7 g/cm(2). Such beam-brushes offer a unique opportunity for treating bulky tumors. We present a case study of a large (4,295 cc clinical target volume) retroperitoneal sarcoma treated to 50.4 Gy relative biological effectiveness (RBE) (presurgery) using a course of photons and protons to the clinical target volume and a course of protons to the gross target volume.
  
  
  RESULTS
  We describe our system and present the dosimetry for all courses and provide an interdosimetric comparison.
  
  
  CONCLUSIONS
  The use of PBS for bulky targets reduces the complexity of treatment planning and delivery compared with collimated proton fields. In addition, PBS obviates, especially for cases as presented here, the significant cost incurred in the construction of field-specific hardware. PBS offers improved dose distributions, reduced treatment time, and reduced cost of treatment.
authors.affiliation: F. H. Burr Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA. hkooy@partners.org
authors.forename: Hanne M
authors.initials: HM
authors.lastname: Kooy
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Clasie
authors.forename: Hsiao-Ming
authors.initials: HM
authors.lastname: Lu
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Madden
authors.forename: Hassan
authors.initials: H
authors.lastname: Bentefour
authors.forename: Nicolas
authors.initials: N
authors.lastname: Depauw
authors.forename: Judy A
authors.initials: JA
authors.lastname: Adams
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Trofimov
authors.forename: Denis
authors.initials: D
authors.lastname: Demaret
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Delaney
authors.forename: Jacob B
authors.initials: JB
authors.lastname: Flanz
mesh_terms: D000465:Algorithms; D006801:Humans; D018208:Liposarcoma, Myxoid / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D061766:Proton Therapy; D020266:Radiotherapy, Conformal / Q000379:methods; D012186:Retroperitoneal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D013679:Technology, Radiologic / Q000379:methods; D013997:Time Factors; D011522:Protons
chemical_list: D011522:Protons