title: Mean apparent diffusion coefficient values in defining radiotherapy planning target volumes in glioblastoma.
abstract: BACKGROUND
  To evaluate mean apparent diffusion coefficient (ADC) values on pre-radiotherapy magnetic resonance (MR) at sites that gave rise to glioblastoma (GBM) recurrence compared to similar surrounding background tissue that did not progress to tumor.
  
  
  METHODS
  Twenty out of 110 consecutive patients with pathology proven GBM treated at our institution from 1/1/2009 to 5/31/2012 had definitive recurrence 6 months following radiotherapy. In this single-center retrospective cohort study, pre- and post-radiotherapy MR brain exams were evaluated. Sites of tumor recurrence on post-therapy exams were co-localized to pre-therapy exams and the background tissue type which gave rise to tumor was noted (i.e., T2 hyperintensity, normal appearing white or gray matter). Similar surrounding background tissue not progressing to tumor was also selected. Two radiologists compared mean ADC values on pre-radiotherapy MR for sites which gave rise to future tumor recurrence and sites of similar background tissue.
  
  
  RESULTS
  Pre-radiotherapy mean ADC values were significantly lower in regions of future tumor recurrence than in regions of surrounding background tissue not progressing to tumor (P=0.003). There were no significant quantitative differences on T1-weighted pre contrast (P=0.50) or T2-weighted (P=0.10) sequences between sites. There was strong interobserver agreement with an intraclass correlation of 0.867 for ADC values at sites of future tumor recurrence and background tissue.
  
  
  CONCLUSIONS
  Mean ADC values may help predict sites of future gross tumor recurrence in GBM, which could be helpful in radiation therapy planning.
authors.affiliation: 1 Department of Radiology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA ; 2 Department of Diagnostic Radiology, Rush University Medical Center, Chicago, IL, USA ; 3 Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Jeong
authors.affiliation: 1 Department of Radiology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA ; 2 Department of Diagnostic Radiology, Rush University Medical Center, Chicago, IL, USA ; 3 Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: Malalis
authors.affiliation: 1 Department of Radiology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA ; 2 Department of Diagnostic Radiology, Rush University Medical Center, Chicago, IL, USA ; 3 Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Arrington
authors.affiliation: 1 Department of Radiology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA ; 2 Department of Diagnostic Radiology, Rush University Medical Center, Chicago, IL, USA ; 3 Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Aaron S
authors.initials: AS
authors.lastname: Field
authors.affiliation: 1 Department of Radiology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA ; 2 Department of Diagnostic Radiology, Rush University Medical Center, Chicago, IL, USA ; 3 Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Jung W
authors.initials: JW
authors.lastname: Choi
authors.affiliation: 1 Department of Radiology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA ; 2 Department of Diagnostic Radiology, Rush University Medical Center, Chicago, IL, USA ; 3 Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Mehmet
authors.initials: M
authors.lastname: Kocak
keywords: Apparent diffusion coefficient (ADC); glioblastoma (GBM); magnetic resonance (MR); tumor recurrence