title: Spot-scanned pancreatic stereotactic body proton therapy: A dosimetric feasibility and robustness study.
abstract: OBJECTIVE
  We explored the dosimetric potential of spot-scanned stereotactic body proton therapy (SBPT) for pancreatic cancer.
  
  
  METHODS
  We compared SBPT to stereotactic body intensity-modulated radiotherapy (SB-IMRT) in 10 patients. We evaluated 3 variables in SBPT planning: (1) 4 and 6 mm spot size; (2) single vs. multi-field optimization (SFO vs. MFO); and (3) optimization target volume (OTV) expansion. Robustness analysis was performed with unidirectional isocenter shifts of ±3 mm in x, y, and z and ±3% stopping power uncertainties.
  
  
  RESULTS
  SBPT plans had lower V10Gy for the stomach and small and large bowels. Under static robustness, a 5 mm OTV and SFO-6 mm spot size represented the best compromise between target and normal structure. A 4-mm spot-size and 3 mm OTV resulted in significant target underdosing with deformable dose accumulation analysis.
  
  
  CONCLUSIONS
  This study provides a critical basis for clinical translation of spot size, optimization technique, and OTV expansion for pancreatic SBPT.
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, 200 First St. SW, Rochester, MN 55901, USA; Department of Radiation Oncology, Mayo Clinic Hospital, 5777 E. Mayo Blvd., Phoenix, AZ 85054, USA.
authors.forename: Terence T
authors.initials: TT
authors.lastname: Sio
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, 200 First St. SW, Rochester, MN 55901, USA.
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Merrell
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, 200 First St. SW, Rochester, MN 55901, USA.
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Beltran
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Hospital, 5777 E. Mayo Blvd., Phoenix, AZ 85054, USA.
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Ashman
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, 200 First St. SW, Rochester, MN 55901, USA.
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Hoeft
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Hospital, 5777 E. Mayo Blvd., Phoenix, AZ 85054, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Miller
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, 200 First St. SW, Rochester, MN 55901, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Whitaker
authors.affiliation: Department of Radiation Oncology, Mayo Clinic, 200 First St. SW, Rochester, MN 55901, USA.
authors.forename: Stephanie K
authors.initials: SK
authors.lastname: Wurgler
authors.affiliation: Department of Radiation Oncology, Mayo Clinic Hospital, 5777 E. Mayo Blvd., Phoenix, AZ 85054, USA. Electronic address: Tryggestad.Erik@mayo.edu.
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Tryggestad
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D008113:Liver Neoplasms / Q000532:radiotherapy; D010190:Pancreatic Neoplasms / Q000532:radiotherapy*; D061766:Proton Therapy / Q000379:methods*; D011874:Radiometry; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted
keywords: Intensity-modulated radiation therapy; Pancreatic cancer; Proton plan robustness; Spot-scanned proton therapy; Stereotactic body proton therapy; Stereotactic body radiation therapy