title: A comparative dosimetric analysis of virtual stereotactic body radiotherapy to high-dose-rate monotherapy for intermediate-risk prostate cancer.
abstract: OBJECTIVE
  Stereotactic body radiotherapy (SBRT) is being used with increasing frequency as definitive treatment of early stage prostate cancer. Much of the justification for its adoption was derived from earlier clinical results using high-dose-rate (HDR) brachytherapy. We determine whether HDR's dosimetry can be achieved by virtual SBRT.
  
  
  METHODS
  Patients with intermediate-risk prostate cancer on a prospective trial evaluating the efficacy of HDR monotherapy treated to dose of 9.5Gy×4 fractions were used for this study. A total of 5 patients were used in this analysis. Virtual SBRT plans were developed to reproduce the planning target volume (PTV) HDR dose distributions. Both normal tissue- and PTV-prioritized plans were generated.
  
  
  RESULTS
  From the normal tissue-prioritized plan, HDR and virtual SBRT achieved similar PTV V100 (93.8% vs. 93.1%, p=0.20) and V150 (40.3% vs. 42.9%, p=0.69) coverage. However, the PTV V200 was not attainable with SBRT (15.2% vs. 0.0%, p<0.001). The rectal Dmax was significantly lower with HDR (94.2% vs. 99.42%, p=0.05). The rectal D2 cc was also lower (60.8% vs. 71.1%, p=0.07). Difference in D1 cc urethral dose was not significantly different (87.7% vs. 75.2%, p=0.33). Comparing the PTV-prioritized plans, the rectal Dmax (94.2% vs. 111.1%, p=0.05) and mean dose (27.1% vs. 33.3%, p=0.03) were significantly higher using SBRT, and the rectal D2 cc was higher using SBRT (60.8% vs. 81.8%, p=0.07).
  
  
  CONCLUSIONS
  HDR achieves significantly higher intraprostatic doses while achieving a lower maximum rectal dose compared with our virtual SBRT treatment planning. Future studies should compare clinical outcomes and toxicity between these modalities.
authors.affiliation: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY. Electronic address: sprattd@mskcc.org.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Spratt
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Scala
authors.forename: Michael
authors.initials: M
authors.lastname: Folkert
authors.forename: Laszlo
authors.initials: L
authors.lastname: Voros
authors.forename: Gil'ad N
authors.initials: GN
authors.lastname: Cohen
authors.forename: Laura
authors.initials: L
authors.lastname: Happersett
authors.forename: Evangelia
authors.initials: E
authors.lastname: Katsoulakis
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Zelefsky
authors.forename: Marisa A
authors.initials: MA
authors.lastname: Kollmeier
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Yamada
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D008297:Male; D009367:Neoplasm Staging; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011874:Radiometry; D011879:Radiotherapy Dosage; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods; D016896:Treatment Outcome
keywords: Brachytherapy; Dosimetry; High-dose rate; Prostate cancer; Stereotactic body radiotherapy