title: A dosimetric comparison of ultra-hypofractionated passively scattered proton radiotherapy and stereotactic body radiotherapy (SBRT) in the definitive treatment of localized prostate cancer.
abstract: BACKGROUND
  We compared target and normal tissue dosimetric indices between ultra-hypofractionated passively scattered proton radiotherapy and stereotactic body radiotherapy (SBRT) in the definitive treatment of localized prostate cancer.
  
  
  METHODS
  Ten patients were treated definitively for localized prostate cancer with SBRT to a dose of 36.25 Gy in 5 fractions prescribed to a volume encompassing the prostate only. Dose-volume constraints were applied to the rectum, bladder, penile bulb, femoral heads, and prostatic and membranous urethra. Three-field passively scattered proton plans were retrospectively generated using target volumes from the same patients. Dosimetric indices were compared between the SBRT and proton plans using the Wilcoxon signed rank test.
  
  
  RESULTS
  All dose constraints were achieved using both ultra-hypofractionated passively scattered proton and SBRT planning. Proton plans demonstrated significant improvement over SBRT in mean dose delivered to the penile bulb (5.2 CGE vs. 11.4 Gy; p=0.002), rectum (6.7 CGE vs. 10.6 Gy; p=0.002), and membranous urethra (32.2 CGE vs. 34.4 Gy; p=0.006) with improved target homogeneity resulting in a significant reduction in hot spots and volumes of tissue exposed to low doses of radiation. Compared to proton planning, SBRT planning resulted in significant improvement in target conformality with a mean index of 1.17 versus 1.72 (p=0.002), resulting in a dose reduction to the volume of bladder receiving more than 90% of the PD (V32.6, 7.5% vs. 15.9%; p=0.01) and mean dose to the left (7.1 Gy vs. 10.4 CGE; p=0.004) and right (4.0 Gy vs. 10.9 CGE; p=0.01) femoral heads.
  
  
  CONCLUSIONS
  Target and normal tissue dose constraints for ultra-hypofractionated definitive radiotherapy of localized prostate cancer are readily achieved using both CK SBRT and passively scattered proton-based therapy suggesting feasibility of either modality.
authors.affiliation: Georgetown University School of Medicine, Department of Radiation Medicine , Washington, DC , USA.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Kole
authors.forename: R Charles
authors.initials: RC
authors.lastname: Nichols
authors.forename: Song
authors.initials: S
authors.lastname: Lei
authors.forename: Binbin
authors.initials: B
authors.lastname: Wu
authors.forename: Soon N
authors.initials: SN
authors.lastname: Huh
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Morris
authors.forename: Sang
authors.initials: S
authors.lastname: Lee
authors.forename: Michael
authors.initials: M
authors.lastname: Tong
authors.forename: Nancy P
authors.initials: NP
authors.lastname: Mendenhall
authors.forename: Anatoly
authors.initials: A
authors.lastname: Dritschilo
authors.forename: Sean P
authors.initials: SP
authors.lastname: Collins
mesh_terms: D005270:Femur Head; D006801:Humans; D008297:Male; D058958:Organs at Risk; D010413:Penis; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D061766:Proton Therapy / Q000379:methods*; D000069473:Radiation Dose Hypofractionation; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum; D014521:Urethra; D001743:Urinary Bladder