title: Nomogram predicting response after chemoradiotherapy in rectal cancer using sequential PETCT imaging: a multicentric prospective study with external validation.
abstract: OBJECTIVE
  To develop and externally validate a predictive model for pathologic complete response (pCR) for locally advanced rectal cancer (LARC) based on clinical features and early sequential (18)F-FDG PETCT imaging.
  
  
  METHODS
  Prospective data (i.a. THUNDER trial) were used to train (N=112, MAASTRO Clinic) and validate (N=78, Università Cattolica del S. Cuore) the model for pCR (ypT0N0). All patients received long-course chemoradiotherapy (CRT) and surgery. Clinical parameters were age, gender, clinical tumour (cT) stage and clinical nodal (cN) stage. PET parameters were SUVmax, SUVmean, metabolic tumour volume (MTV) and maximal tumour diameter, for which response indices between pre-treatment and intermediate scan were calculated. Using multivariate logistic regression, three probability groups for pCR were defined.
  
  
  RESULTS
  The pCR rates were 21.4% (training) and 23.1% (validation). The selected predictive features for pCR were cT-stage, cN-stage, response index of SUVmean and maximal tumour diameter during treatment. The models' performances (AUC) were 0.78 (training) and 0.70 (validation). The high probability group for pCR resulted in 100% correct predictions for training and 67% for validation. The model is available on the website www.predictcancer.org.
  
  
  CONCLUSIONS
  The developed predictive model for pCR is accurate and externally validated. This model may assist in treatment decisions during CRT to select complete responders for a wait-and-see policy, good responders for extra RT boost and bad responders for additional chemotherapy.
authors.affiliation: Department of Radiation Oncology (MAASTRO), Maastricht University Medical Centre, The Netherlands. Electronic address: ruud.vanstiphout@maastro.nl.
authors.forename: Ruud G P M
authors.initials: RG
authors.lastname: van Stiphout
authors.affiliation: Radiotherapy Department, Università Cattolica S. Cuore, Rome, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Valentini
authors.affiliation: Department of Radiation Oncology (MAASTRO), Maastricht University Medical Centre, The Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Buijsen
authors.affiliation: Department of Radiation Oncology (MAASTRO), Maastricht University Medical Centre, The Netherlands; Department of Radiotherapy, MediClin Robert Janker Klinik, Bonn, Germany.
authors.forename: Guido
authors.initials: G
authors.lastname: Lammering
authors.affiliation: Radiotherapy Department, Università Cattolica S. Cuore, Rome, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Meldolesi
authors.affiliation: Department of Radiation Oncology (MAASTRO), Maastricht University Medical Centre, The Netherlands.
authors.forename: Johan
authors.initials: J
authors.lastname: van Soest
authors.affiliation: Department of Nuclear Medicine, Università Cattolica S. Cuore, Rome, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Leccisotti
authors.affiliation: Department of Nuclear Medicine, Università Cattolica S. Cuore, Rome, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Giordano
authors.affiliation: Bioimmagini e Scienze Radiologiche, Università Cattolica S. Cuore, Rome, Italy.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Gambacorta
authors.affiliation: Department of Radiation Oncology (MAASTRO), Maastricht University Medical Centre, The Netherlands.
authors.forename: Andre
authors.initials: A
authors.lastname: Dekker
authors.affiliation: Department of Radiation Oncology (MAASTRO), Maastricht University Medical Centre, The Netherlands.
authors.forename: Philippe
authors.initials: P
authors.lastname: Lambin
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D059248:Chemoradiotherapy; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D009367:Neoplasm Staging; D049451:Nomograms; D049268:Positron-Emission Tomography / Q000379:methods; D011336:Probability; D011446:Prospective Studies; D012004:Rectal Neoplasms / Q000175:diagnosis / Q000628:therapy*; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: (18)F-FDG PET imaging; External validation; Outcome prediction; Prospective study; Rectal cancer; Tumour response