title: Parameters for the Lyman Kutcher Burman (LKB) model of Normal Tissue Complication Probability (NTCP) for specific rectal complications observed in clinical practise.
abstract: OBJECTIVE
  The Normal Tissue Complication Probability (NTCP) for rectum is usually defined for late rectal bleeding. This study calculates NTCP parameter values for additional rectal toxicity endpoints observed in clinical practise.
  
  
  METHODS
  388 patients from the multicentre MRC-RT01 prostate conformal radiotherapy trial (ISRCTN 47772397) were used to derive independent Lyman Kutcher Burman model (LKB) parameters for five late rectal toxicity endpoints: rectal bleeding, proctitis, stool frequency, loose stools and rectal urgency. The parameters were derived using maximum likelihood estimation. Bootstrap and leave-one-out methods were employed to test the generalisability of the results for use in a general population.
  
  
  RESULTS
  A consistent pattern of increasing value of TD50(1) for Grade 2 toxicity only compared to Grades 1 and 2 toxicity was observed for all endpoints. Parameter values varied between endpoints (particularly for the volume parameter n). TD50(1), m and n were 68.5 Gy (95% CI)(66.8-70.8), 0.15 (0.13-0.17) and 0.13 (0.10-0.17), respectively, for G2 rectal bleeding. Bootstrap and leave-one-out results showed that the rectal bleeding and proctitis parameter fits were extremely robust.
  
  
  CONCLUSIONS
  The variation between the values derived for different endpoints may indicate different patho-physiological responses of the rectum to radiation. Therefore different parameter sets would be required to predict specific rectal toxicity endpoints.
authors: Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, UK. Sarah.Gulliford@icr.ac.uk
authors: Sarah L
authors: SL
authors: Gulliford
authors: Mike
authors: M
authors: Partridge
authors: Matthew R
authors: MR
authors: Sydes
authors: Steve
authors: S
authors: Webb
authors: Philip M
authors: PM
authors: Evans
authors: David P
authors: DP
authors: Dearnaley
mesh_terms: D023381:Endpoint Determination; D006471:Gastrointestinal Hemorrhage / Q000209:etiology*; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D011336:Probability; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal / Q000009:adverse effects*; D012007:Rectum / Q000528:radiation effects*