title: Delineation of gross tumor volume (GTV) for radiation treatment planning of locally advanced rectal cancer using information from MRI or FDG-PET/CT: a prospective study.
abstract: OBJECTIVE
  Accurate delineation of target volumes is important to maximize radiation dose to the tumor and minimize it to nontumor tissue. Computed tomography (CT) and magnetic resonance imaging (MRI) are standard imaging modalities in rectal cancer. The aim was to explore whether functional imaging with F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET), combined with CT (FDG-PET/CT) gives additional information to standard pretreatment evaluation and changes the shape and size of the gross tumor volume (GTV).
  
  
  METHODS
  From 2007 to 2009, 77 consecutive patients with locally advanced rectal cancer were prospectively screened for inclusion in the study at two university hospitals in Sweden, and 68 patients were eligible. Standard GTV was delineated using information from clinical examination, CT, and MRI (GTV-MRI). Thereafter, a GTV-PET was defined in the fused PET-CT, and the target volume delineations were compared for total volume, overlap, and mismatch. Pathologic uptake suspect of metastases was also registered.
  
  
  RESULTS
  The median volume of GTV-MRI was larger than that of GTV-PET: 111 cm(3) vs. 87 cm(3) (p < 0.001). In many cases, the GTV-MRI contained the GTV defined on the PET/CT images as subvolumes, but when a GTV total was calculated after the addition of GTV-PET to GTV-MRI, the volume increased, with median 11% (range, 0.5-72%). New lesions were seen in 15% of the patients for whom PET/CT was used.
  
  
  CONCLUSIONS
  FDG-PET/CT facilitates and adds important information to the standard delineation procedure of locally advanced rectal cancer, mostly resulting in a smaller GTV, but a larger total GTV using the union of GTV-MRI and GTV-PET. New lesions were sometimes seen, potentially changing the treatment strategy.
authors.affiliation: Oslo University Hospital, Department of Oncology, Oslo, Norway. mortbrae@medisin.uio.no
authors.forename: Morten
authors.initials: M
authors.lastname: Brændengen
authors.forename: Karl
authors.initials: K
authors.lastname: Hansson
authors.forename: Calin
authors.initials: C
authors.lastname: Radu
authors.forename: Albert
authors.initials: A
authors.lastname: Siegbahn
authors.forename: Hans
authors.initials: H
authors.lastname: Jacobsson
authors.forename: Bengt
authors.initials: B
authors.lastname: Glimelius
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D019275:Radiopharmaceuticals; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000532:radiotherapy; D013548:Sweden; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18