title: Dose-response relations for anal sphincter regarding fecal leakage and blood or phlegm in stools after radiotherapy for prostate cancer. Radiobiological study of 65 consecutive patients.
abstract: BACKGROUND
  The estimation of the parameters that describe the dose-response relations of anal sphincter regarding the clinical endpoints of fecal leakage and blood or phlegm in stools is important in the optimization of prostate cancer radiotherapy. Also, the validity of the relative seriality model for this clinical case needs to be examined by associating the clinical follow-up results with the predicted complication rates.
  
  
  METHODS
  In this study, 65 patients who received radiation therapy for clinically localized prostate adenocarcinoma are analyzed. The clinical treatment outcome and the three-dimensional dose distribution delivered to anal sphincter were available for each patient. A questionnaire was used for assessing the clinical bowel and urinary symptoms. A maximum likelihood fitting was performed to calculate the best estimates of the parameters used by the relative seriality model. The clinical utilization of the calculated parameters in predicting anal sphincter complication probabilities was illustrated by applying the best estimate of the parameters to a subset of the patient population.
  
  
  RESULTS
  The estimated values of the parameters for the two clinical endpoints are D (50) = 70.2 Gy, gamma = 1.22, s = 0.35 for fecal leakage and D (50) = 74.0 Gy, gamma = 0.75, s approximately 0 for blood or phlegm in stools. The standard deviations of the parameters were also calculated together with the confidence intervals of the dose-response curves. The analysis proved that the treatment outcome pattern of the patient material can suitably be reproduced by the relative seriality model (probability of finding a worse fit = 60.2%, the area under the receiver operating characteristic curve = 0.72 and 0.69 and chi(2)-test = 0.97 and 0.86, respectively).
  
  
  CONCLUSIONS
  Fecal leakage is characterized by a medium relative seriality whereas blood or phlegm in stools was found to have strong volume dependence (low relative seriality). Diminishing the biologically effective uniform dose to anal sphincter < 40-45 Gy may significantly reduce the risk of fecal leakage or blood or phlegm in stools for patients irradiated for prostate cancer.
authors.affiliation: Department of Medical Radiation Physics, Karolinska Institutet and Stockholm University, Sweden. panayiotis.mavroidis@radfys.ki.se
authors.forename: Panayiotis
authors.initials: P
authors.lastname: Mavroidis
authors.forename: Massoud
authors.initials: M
authors.lastname: al-Abany
authors.forename: Asgeir R
authors.initials: AR
authors.lastname: Helgason
authors.forename: Anna-Karin
authors.initials: AK
authors.lastname: Agren Cronqvist
authors.forename: Peter
authors.initials: P
authors.lastname: Wersäll
authors.forename: Helena
authors.initials: H
authors.lastname: Lind
authors.forename: Eva
authors.initials: E
authors.lastname: Qvanta
authors.forename: Kyriaki
authors.initials: K
authors.lastname: Theodorou
authors.forename: Constantin
authors.initials: C
authors.lastname: Kappas
authors.forename: Bengt K
authors.initials: BK
authors.lastname: Lind
authors.forename: Gunnar
authors.initials: G
authors.lastname: Steineck
authors.forename: Anders
authors.initials: A
authors.lastname: Brahme
mesh_terms: D000368:Aged; D001003:Anal Canal / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005242:Fecal Incontinence / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009780:Occult Blood; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011877:Radionuclide Imaging; D011878:Radiotherapy / Q000009:adverse effects* / Q000379:methods