title: Evaluation of image-guided radiation therapy (IGRT) technologies and their impact on the outcomes of hypofractionated prostate cancer treatments: a radiobiologic analysis.
abstract: OBJECTIVE
  To quantify the mitigation of geometric uncertainties achieved with the application of various patient setup techniques during the delivery of hypofractionated prostate cancer treatments, using tumor control probability (TCP) and normal tissue complication probability.
  
  
  METHODS
  Five prostate cancer patients with approximately 16 treatment CT studies, taken during the course of their radiation therapy (77 total), were analyzed. All patients were planned twice with an 18 MV six-field conformal technique, with 10- and 5-mm margin sizes, with various hypofractionation schedules (5 to 35 fractions). Subsequently, four clinically relevant patient setup techniques (laser guided and image guided) were simulated to deliver such schedules.
  
  
  RESULTS
  As hypothesized, the impact of geometric uncertainties on clinical outcomes increased with more hypofractionated schedules. However, the absolute gain in TCP due to hypofractionation (up to 21.8% increase) was significantly higher compared with the losses due to geometric uncertainties (up to 8.6% decrease).
  
  
  CONCLUSIONS
  The results of this study suggest that, although the impact of geometric uncertainties on the treatment outcomes increases as the number of fractions decrease, the reduction in TCP due to the uncertainties does not significantly offset the expected theoretical gain in TCP by hypofractionation.
authors.affiliation: Radiation Treatment Program, London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada.
authors.forename: William Y
authors.initials: WY
authors.lastname: Song
authors.forename: Bryan
authors.initials: B
authors.lastname: Schaly
authors.forename: Glenn
authors.initials: G
authors.lastname: Bauman
authors.forename: Jerry J
authors.initials: JJ
authors.lastname: Battista
authors.forename: Jake
authors.initials: J
authors.lastname: Van Dyk
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D007834:Lasers; D008297:Male; D011336:Probability; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011853:Radiobiology; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods / Q000592:standards*; D020266:Radiotherapy, Conformal / Q000379:methods / Q000592:standards*; D014057:Tomography, X-Ray Computed