title: Computed tomography assessment of response to therapy: tumor volume change measurement, truth data, and error.
abstract: OBJECTIVE
  This article describes issues and methods that are specific to the measurement of change in tumor volume as measured from computed tomographic (CT) images and how these would relate to the establishment of CT tumor volumetrics as a biomarker of patient response to therapy. The primary focus is on the measurement of lung tumors, but the approach should be generalizable to other anatomic regions.
  
  
  METHODS
  The first issues addressed are the various sources of bias and variance in the measurement of tumor volumes, which are discussed in the context of measurement variation and its impact on the early detection of response to therapy. RESULTS AND RESOURCES: Research that seeks to identify the magnitude of some of these sources of error is ongoing, and several of these efforts are described herein. In addition, several resources for these investigations are being made available through the National Institutes of Health-funded Reference Image Database to Evaluate Response to therapy in cancer project, and these are described as well. Other measures derived from CT image data that might be predictive of patient response are described briefly, as well as the additional issues that each of these metrics may encounter in real-life applications.
  
  
  CONCLUSIONS
  The article concludes with a brief discussion of moving from the assessment of measurement variation to the steps necessary to establish the efficacy of a metric as a biomarker for response.
authors: Department of Radiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
authors: Michael F
authors: MF
authors: McNitt-Gray
authors: Luc M
authors: LM
authors: Bidaut
authors: Samuel G
authors: SG
authors: Armato
authors: Charles R
authors: CR
authors: Meyer
authors: Marios A
authors: MA
authors: Gavrielides
authors: Charles
authors: C
authors: Fenimore
authors: Geoffrey
authors: G
authors: McLennan
authors: Nicholas
authors: N
authors: Petrick
authors: Binsheng
authors: B
authors: Zhao
authors: Anthony P
authors: AP
authors: Reeves
authors: Reinhard
authors: R
authors: Beichel
authors: Hyun-Jung Grace
authors: HJ
authors: Kim
authors: Lisa
authors: L
authors: Kinnard