title: Volumetric-modulated arc stereotactic body radiotherapy for prostate cancer: dosimetric impact of an increased near-maximum target dose and of a rectal spacer.
abstract: OBJECTIVE
  In volumetric-modulated arc therapy (VMAT) prostate stereotactic body radiotherapy (SBRT), dose coverage of the planning target volume (PTV) becomes challenging when the sparing of rectum, bladder and urethra is strictly pursued. Our current 35-Gy-in-five-fraction plans only assure 33.2 Gy to ≥95% PTV ([Formula: see text] ≥ 95%). Looking for an improved [Formula: see text], increased near-maximum target dose (D2%) and prostate-rectum spacer insertion were tested.
  
  
  METHODS
  For 11 patients, two VMAT plans, with D2% ≤ 37.5 Gy (Hom) or D2% ≤ 40.2 Gy (Het), on each of two CT studies, before or after spacer insertion, were computed. All plans assured [Formula: see text] ≥95%, and <1 cm(3) of rectum, bladder and urethra receiving ≥35 Gy. By hypothesis testing, several dose-volume metrics for target coverage and rectal sparing were compared across the four groups of plans. The impact of spacer insertion on the fractions of rectum receiving more than 18, 28 and 32 Gy ([Formula: see text]) was further tested by linear correlation analysis.
  
  
  RESULTS
  By hypothesis testing, the increased D2% was associated with improvements in target coverage, whereas spacer insertion was associated with improvements in both target coverage and rectal [Formula: see text]. By linear correlation analysis, spacer insertion was related to the reductions in rectal [Formula: see text] for X ≥ 28 Gy.
  
  
  CONCLUSIONS
  A slightly increased D2% or the use of spacer insertion was each able to improve [Formula: see text]. Their combined use assured [Formula: see text] ≥ 98% to all our patients. Spacer insertion was further causative for improvements in rectal sparing.
  
  
  CONCLUSIONS
  For VMAT plans in prostate SBRT, the distinct dosimetric usefulness of increased D2% and of the use of spacer insertion were validated in terms of target coverage and rectal sparing.
authors.affiliation: 1 Radiation Oncology, Ospedale Sacro Cuore Don Calabria, Verona, Italy.
authors.forename: Ruggero
authors.initials: R
authors.lastname: Ruggieri
authors.affiliation: 1 Radiation Oncology, Ospedale Sacro Cuore Don Calabria, Verona, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Naccarato
authors.affiliation: 1 Radiation Oncology, Ospedale Sacro Cuore Don Calabria, Verona, Italy.
authors.forename: Pavel
authors.initials: P
authors.lastname: Stavrev
authors.affiliation: 1 Radiation Oncology, Ospedale Sacro Cuore Don Calabria, Verona, Italy.
authors.forename: Nadejda
authors.initials: N
authors.lastname: Stavreva
authors.affiliation: 1 Radiation Oncology, Ospedale Sacro Cuore Don Calabria, Verona, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Fersino
authors.affiliation: 1 Radiation Oncology, Ospedale Sacro Cuore Don Calabria, Verona, Italy.
authors.forename: Niccolò
authors.initials: N
authors.lastname: Giaj Levra
authors.affiliation: 1 Radiation Oncology, Ospedale Sacro Cuore Don Calabria, Verona, Italy.
authors.forename: Rosario
authors.initials: R
authors.lastname: Mazzola
authors.affiliation: 2 Radiotherapy and Radiosurgery Department, IRCCS Istituto Clinico Humanitas, Milan, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Mancosu
authors.affiliation: 2 Radiotherapy and Radiosurgery Department, IRCCS Istituto Clinico Humanitas, Milan, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Scorsetti
authors.affiliation: 1 Radiation Oncology, Ospedale Sacro Cuore Don Calabria, Verona, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: Alongi
mesh_terms: D000368:Aged; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D059351:Organ Sparing Treatments / Q000379:methods; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D016634:Radiosurgery / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate