title: A tumor control probability model for anal squamous cell carcinoma.
abstract: OBJECTIVE
  A recent update of the RTOG 9811, reported differing relapse rates for early and late anal squamous cell carcinoma following chemoradiotherapy (CRT). There may be a role for dose-individualization, however the dose-response relationship for anal cancer is not currently known. Intensity-modulated radiotherapy (IMRT) has been widely adopted with multiple series published. The aim is to fit a tumor control probability (TCP) model to the published IMRT data.
  
  
  METHODS
  We performed a systematic review of PubMed and Embase databases to identify thirteen appropriate papers, including 625 patients. Predefined data fields were collected. A standard linear quadratic TCP model, which included repopulation, was fit by least squares minimization.
  
  
  RESULTS
  The fitted TCP curve demonstrated a dose-response relationship with α=0.196 Gy(-1). The curve suggests: in early stage tumours, a dose reduction from 50 Gy to 45 Gy reduces 2 year local control from 98% to 95%; in late stage tumours, a dose escalation from 50 Gy to 55 Gy improves the 2 year local control rate from approximately 50% to 80%.
  
  
  CONCLUSIONS
  The published data are broadly consistent with a linear quadratic dose-response model. Dose-individualization in anal cancer should be further investigated in the context of clinical trials.
authors.affiliation: Department of Oncology, CRUK/MRC Oxford Institute for Radiation Oncology, University of Oxford, United Kingdom. Electronic address: rebecca.muirhead@oncology.ox.ac.uk.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Muirhead
authors.affiliation: Department of Oncology, CRUK/MRC Oxford Institute for Radiation Oncology, University of Oxford, United Kingdom.
authors.forename: Mike
authors.initials: M
authors.lastname: Partridge
authors.affiliation: Department of Oncology, CRUK/MRC Oxford Institute for Radiation Oncology, University of Oxford, United Kingdom.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Hawkins
mesh_terms: D001005:Anus Neoplasms / Q000532:radiotherapy*; D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D016018:Least-Squares Analysis; D016014:Linear Models; D009364:Neoplasm Recurrence, Local / Q000532:radiotherapy; D011336:Probability; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods / Q000706:statistics & numerical data*
keywords: Anal cancer; Dose de-escalation; Dose escalation; Modelling; TCP