title: Quantitative imaging to assess tumor response to therapy: common themes of measurement, truth data, and error sources.
abstract: BACKGROUND
  Early detection of tumor response to therapy is a key goal. Finding measurement algorithms capable of early detection of tumor response could individualize therapy treatment as well as reduce the cost of bringing new drugs to market. On an individual basis, the urgency arises from the desire to prevent continued treatment of the patient with a high-cost and/or high-risk regimen with no demonstrated individual benefit and rapidly switch the patient to an alternative efficacious therapy for that patient. In the context of bringing new drugs to market, such algorithms could demonstrate efficacy in much smaller populations, which would allow phase 3 trials to achieve statistically significant decisions with fewer subjects in shorter trials.
  
  
  METHODS
  This consensus-based article describes multiple, image modality-independent means to assess the relative performance of algorithms for measuring tumor change in response to therapy. In this setting, we describe specifically the example of measurement of tumor volume change from anatomic imaging as well as provide an overview of other promising generic analytic methods that can be used to assess change in heterogeneous tumors. To support assessment of the relative performance of algorithms for measuring small tumor change, data sources of truth are required.
  
  
  RESULTS
  Very short interval clinical imaging examinations and phantom scans provide known truth for comparative evaluation of algorithms.
  
  
  CONCLUSIONS
  For a given category of measurement methods, the algorithm that has the smallest measurement noise and least bias on average will perform best in early detection of true tumor change.
authors: Department of Radiology, University of Michigan, Ann Arbor, MI, USA.
authors: Charles R
authors: CR
authors: Meyer
authors: Samuel G
authors: SG
authors: Armato
authors: Charles P
authors: CP
authors: Fenimore
authors: Geoffrey
authors: G
authors: McLennan
authors: Luc M
authors: LM
authors: Bidaut
authors: Daniel P
authors: DP
authors: Barboriak
authors: Marios A
authors: MA
authors: Gavrielides
authors: Edward F
authors: EF
authors: Jackson
authors: Michael F
authors: MF
authors: McNitt-Gray
authors: Paul E
authors: PE
authors: Kinahan
authors: Nicholas
authors: N
authors: Petrick
authors: Binsheng
authors: B
authors: Zhao