title: How to study optimal timing of PET/CT for monitoring of cancer treatment.
abstract: OBJECTIVE
  The use of PET/CT for monitoring treatment response in cancer patients after chemo- or radiotherapy is a very promising approach to optimize cancer treatment. However, the timing of the PET/CT-based evaluation of reduction in viable tumor tissue is a crucial question. We investigated how to plan and analyze studies to optimize this timing.
  
  
  METHODS
  General considerations about studying the optimal timing are given and four fundamental steps are illustrated using data from a published study.
  
  
  RESULTS
  The optimal timing should be examined by optimizing the schedule with respect to predicting the overall individual time course we can observe in the case of dense measurements. The optimal timing needs not to and should not be studied by optimizing the association with the prognosis of the patient.
  
  
  CONCLUSIONS
  The optimal timing should be examined in specific 'schedule optimizing studies'. These should be clearly distinguished from studies evaluating the prognostic value of a reduction in viable tumor tissue.
authors.affiliation: Clinical Epidemiology, Institute of Medical Biometry and Medical Informatics, University Medical Center Freiburg Stefan-Meier-Str. 26, D-79104 Freiburg, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Vach
authors.forename: Poul Flemming
authors.initials: PF
authors.lastname: Høilund-Carlsen
authors.forename: Barbara Malene
authors.initials: BM
authors.lastname: Fischer
authors.forename: Oke
authors.initials: O
authors.lastname: Gerke
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Weber
keywords: cancer; optimal schedule; prognostic value; response evaluation