title: Proctitis 1 Week after Stereotactic Body Radiation Therapy for Prostate Cancer: Implications for Clinical Trial Design.
abstract: BACKGROUND
  Proctitis following prostate cancer radiation therapy is a primary determinant of quality of life (QOL). While previous studies have assessed acute rectal morbidity at 1 month after stereotactic body radiotherapy (SBRT), little data exist on the prevalence and severity of rectal morbidity within the first week following treatment. This study reports the acute bowel morbidity 1 week following prostate SBRT.
  
  
  METHODS
  Between May 2013 and August 2014, 103 patients with clinically localized prostate cancer were treated with 35-36.25 Gy in five fractions using robotic SBRT delivered on a prospective clinical trial. Bowel toxicity was graded using the Common Terminology Criteria for Adverse Events version 4.0 (CTCAEv.4). Bowel QOL was assessed using the EPIC-26 questionnaire bowel domain at baseline, 1 week, 1 month, and 3 months. Time-dependent changes in bowel symptoms were statistically compared using the Wilcoxon signed-rank test. Clinically significant change was assessed by the minimally important difference (MID) in EPIC score. This was defined as a change of 1/2 standard deviation (SD) from the baseline score.
  
  
  RESULTS
  One-hundred and three patients with a minimum of 3 months of follow-up were analyzed. The cumulative incidence of acute grade 2 gastrointestinal (GI) toxicity was 23%. There were no acute ≥ grade 3 bowel toxicities. EPIC bowel summary scores maximally declined at 1 week after SBRT (-13.9, p < 0.0001) before returning to baseline at 3 months after SBRT (+0.03, p = 0.94). Prior to treatment, 4.9% of men reported that their bowel bother was a moderate to big problem. This increased to 28.4% (p < 0.0001) 1 week after SBRT and returned to baseline at 3 months after SBRT (0.0%, p = 0.66). Only the bowel summary and bowel bother score declines at 1 week met the MID threshold for clinically significant change.
  
  
  CONCLUSIONS
  The rate and severity of acute proctitis following prostate SBRT peaked at 1 week after treatment and returned to baseline by 3 months. Toxicity assessment at 1 week can therefore minimize recall bias and should aid in the design of future clinical trials focused on accurately capturing and minimizing acute morbidity following SBRT.
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Ima
authors.initials: I
authors.lastname: Paydar
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Robyn A
authors.initials: RA
authors.lastname: Cyr
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Yung
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Siyuan
authors.initials: S
authors.lastname: Lei
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Brian Timothy
authors.initials: BT
authors.lastname: Collins
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Leonard N
authors.initials: LN
authors.lastname: Chen
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Simeng
authors.initials: S
authors.lastname: Suy
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Anatoly
authors.initials: A
authors.lastname: Dritschilo
authors.affiliation: Department of Urology, Georgetown University Hospital , Washington, DC , USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Lynch
authors.affiliation: Department of Radiation Medicine, Georgetown University Hospital , Washington, DC , USA.
authors.forename: Sean P
authors.initials: SP
authors.lastname: Collins
keywords: CyberKnife; EPIC; SBRT; prostate cancer; recall period; symptom management trial; time point