title: Impact of the EARL harmonization program on automatic delineation of metabolic active tumour volumes (MATVs).
abstract: BACKGROUND
  The clinical validation of the EARL harmonization program for standardised uptake value (SUV) metrics is well documented; however, its potential for defining metabolic active tumour volume (MATV) has not yet been investigated. We aimed to compare delineation of MATV on images reconstructed using conventional ordered subset expectation maximisation (OSEM) with those reconstructed using point spread function modelling (PSF-reconstructed images), and either optimised for diagnostic potential (PSF) or filtered to meet the EANM/EARL harmonising standards (PSF7).
  
  
  METHODS
  Images from 18 stage IIIA-IIIB lung cancer patients were reconstructed using all the three methods. MATVs were then delineated using both a 40% isocontour and a gradient-based method. MATVs were compared by means of Bland-Altman analyses, and Dice coefficients and concordance indices based on the unions and intersections between each pair of reconstructions (PSF vs OSEM, PSF7vs PSF and PSF7vs OSEM).
  
  
  RESULTS
  Using the 40% isocontour method and taking the MATVs delineated on OSEM images as a reference standard, the use of PSF7images led to significantly higher Dice coefficients (median value = 0.96 vs 0.77; P < 0.0001) and concordance indices (median value = 0.92 vs 0.64; P < 0.0001) than those obtained using PSF images. The gradient-based methodology was less sensitive to reconstruction variability than the 40% isocontour method; Dice coefficients and concordance indices were superior to 0.8 for both PSF reconstruction methods. However, the use of PSF7images led to narrower interquartile ranges and significantly higher Dice coefficients (median value = 0.96 vs 0.94; P = 0.01) and concordance indices (median value = 0.89 vs 0.85; P = 0.003) than those obtained with PSF images.
  
  
  CONCLUSIONS
  This study demonstrates that automatic contouring of lung tumours on EARL-compliant PSF images using the widely adopted automatic isocontour methodology is an accurate means of overcoming reconstruction variability in MATV delineation. Although gradient-based methodology appears to be less sensitive to reconstruction variability, the use of EARL-compliant PSF images significantly improved the Dice coefficients and concordance indices, demonstrating the importance of harmonised-images, even when more advanced contouring algorithms are used.
authors.affiliation: Nuclear Medicine Department, François Baclesse Cancer Centre, Caen, France.|INSERM U1086 « ANTICIPE », BioTICLA, François Baclesse Cancer Centre, Caen, France.
authors.forename: Charline
authors.initials: C
authors.lastname: Lasnon
authors.affiliation: Nuclear Medicine Department, University Hospital, Avenue Côte de Nacre, 14000, Caen, France.
authors.forename: Blandine
authors.initials: B
authors.lastname: Enilorac
authors.affiliation: Radiation Oncology, François Baclesse Cancer Centre, Caen, France.
authors.forename: Hosni
authors.initials: H
authors.lastname: Popotte
authors.affiliation: INSERM U1086 « ANTICIPE », BioTICLA, François Baclesse Cancer Centre, Caen, France. aide-n@chu-caen.fr.|Nuclear Medicine Department, University Hospital, Avenue Côte de Nacre, 14000, Caen, France. aide-n@chu-caen.fr.|Normandie University, Caen, France. aide-n@chu-caen.fr.
authors.forename: Nicolas
authors.identifier: http://orcid.org/0000-0001-9207-0847
authors.initials: N
authors.lastname: Aide
keywords: EARL accreditation program; FDG; Harmonization; MATV; PET