title: Integrating respiratory-gated PET-based target volume delineation in liver SBRT planning, a pilot study.
abstract: BACKGROUND
  To assess the feasibility and benefit of integrating four-dimensional (4D) Positron Emission Tomography (PET) - computed tomography (CT) for liver stereotactic body radiation therapy (SBRT) planning.
  
  
  METHODS
  8 patients with 14 metastases were accrued in the study. They all underwent a non-gated PET and a 4D PET centered on the liver. The same CT scan was used for attenuation correction, registration, and considered the planning CT for SBRT planning. Six PET phases were reconstructed for each 4D PET. By applying an individualized threshold to the 4D PET, a Biological Internal Target Volume (BITV) was generated for each lesion. A gated Planning Target Volume (PTVg) was created by adding 3 mm to account for set-up margins. This volume was compared to a manual Planning Target Volume (PTV) delineated with the help of a semi-automatic Biological Target Volume (BTV) obtained from the non-gated exam. A 5 mm radial and a 10 mm craniocaudal margins were applied to account for tumor motion and set-up margins to create the PTV.
  
  
  RESULTS
  One undiagnosed liver metastasis was discovered thanks to the 4D PET. The semi-automatic BTV were significantly smaller than the BITV (p = 0.0031). However, after applying adapted margins, 4D PET allowed a statistically significant decrease in the PTVg as compared to the PTV (p = 0.0052).
  
  
  CONCLUSIONS
  In comparison to non-gated PET, 4D PET may better define the respiratory movements of liver targets and improve SBRT planning for liver metastases. Furthermore, non respiratory-gated PET exams can both misdiagnose liver metastases and underestimate the real internal target volumes.
authors.affiliation: Radiotherapy Department, Montpellier Cancer Institute - Val d'Aurelle, 208 rue des Apothicaires, F-34298 Montpellier Cedex 5, France. riouo@hotmail.com.
authors.forename: Olivier
authors.initials: O
authors.lastname: Riou
authors.forename: Benjamin
authors.initials: B
authors.lastname: Serrano
authors.forename: David
authors.initials: D
authors.lastname: Azria
authors.forename: Benoit
authors.initials: B
authors.lastname: Paulmier
authors.forename: Remy
authors.initials: R
authors.lastname: Villeneuve
authors.forename: Pascal
authors.initials: P
authors.lastname: Fenoglietto
authors.forename: Antonella
authors.initials: A
authors.lastname: Artenie
authors.forename: Cécile
authors.initials: C
authors.lastname: Ortholan
authors.forename: Marc
authors.initials: M
authors.lastname: Faraggi
authors.forename: Juliette
authors.initials: J
authors.lastname: Thariat
mesh_terms: D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D021621:Imaging, Three-Dimensional; D008113:Liver Neoplasms / Q000000981:diagnostic imaging* / Q000556:secondary / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D009369:Neoplasms / Q000473:pathology* / Q000628:therapy; D019047:Phantoms, Imaging; D010865:Pilot Projects; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D011446:Prospective Studies; D016634:Radiosurgery; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden