title: The impact of positron emission tomography/computed tomography in edge delineation of gross tumor volume for head and neck cancers.
abstract: OBJECTIVE
  To study anatomic biologic contouring (ABC), using a previously described distinct halo, to unify volume contouring methods in treatment planning for head and neck cancers.
  
  
  METHODS
  Twenty-five patients with head and neck cancer at various sites were planned for radiation therapy using positron emission tomography/computed tomography (PET/CT). The ABC halo was used in all PET/CT scans to contour the gross tumor volume (GTV) edge. The CT-based GTV (GTV-CT) and PET/CT-based GTV (GTV-ABC) were contoured by two independent radiation oncologists.
  
  
  RESULTS
  The ABC halo was observed in all patients studied. The halo had a standard unit value of 2.19 +/- 0.28. The mean halo thickness was 2.02 +/- 0.21 mm. Significant volume modification (>or=25%) was seen in 17 of 25 patients (68%) after implementation of GTV-ABC. Concordance among observers was increased with the use of the halo as a guide for GTV determination: 6 patients (24%) had a <or=10% volume discrepancy with CT alone, compared with 22 (88%) with PET/CT (p < 0.001). Interobserver variability decreased from a mean GTV difference of 20.3 cm3 in CT-based planning to 7.2 cm3 in PET/CT-based planning (p < 0.001).
  
  
  CONCLUSIONS
  Using the "anatomic biologic halo" to contour GTV in PET/CT improves consistency among observers. The distinctive appearance of the described halo and its presence in all of the studied tumors make it attractive for GTV contouring in head and neck tumors. Additional studies are needed to confirm the correlation of the halo with presence of malignant cells.
authors.affiliation: Department of Radiation Oncology, New York Methodist Hospital, Weill Medical College of Cornell University, New York, NY, USA. hashamalla@aol.com
authors.forename: Hani
authors.initials: H
authors.lastname: Ashamalla
authors.forename: Adel
authors.initials: A
authors.lastname: Guirgius
authors.forename: Ewa
authors.initials: E
authors.lastname: Bieniek
authors.forename: Sameer
authors.initials: S
authors.lastname: Rafla
authors.forename: Alex
authors.initials: A
authors.lastname: Evola
authors.forename: Ganesh
authors.initials: G
authors.lastname: Goswami
authors.forename: Randall
authors.initials: R
authors.lastname: Oldroyd
authors.forename: Bahaa
authors.initials: B
authors.lastname: Mokhtar
authors.forename: Kapila
authors.initials: K
authors.lastname: Parikh
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D019788:Fluorodeoxyglucose F18; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D049268:Positron-Emission Tomography / Q000379:methods*; D011446:Prospective Studies; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18