title: Biological image-guided radiotherapy in rectal cancer: is there a role for FMISO or FLT, next to FDG?
abstract: OBJECTIVE
  The purpose of this study is to investigate the use of PET/CT with fluorodeoxyglucose (FDG), fluorothymidine (FLT) and fluoromisonidazole (FMISO) for radiotherapy (RT) target definition and evolution in rectal cancer.
  
  
  METHODS
  PET/CT was performed before and during preoperative chemoradiotherapy (CRT) in 15 patients with resectable rectal cancer. PET signals were delineated and CT images on the different time points were non-rigidly registered. Mismatch analyses were carried out to quantify the overlap between FDG and FLT or FMISO tumour volumes (TV) and between PET TVs over time.
  
  
  RESULTS
  Ninety sequential PET/CT images were analyzed. The mean FDG, FLT and FMISO-PET TVs showed a tendency to shrink during preoperative CRT. On each time point, the mean FDG-PET TV was significantly larger than the FMISO-PET TV but not significantly larger than the mean FLT-PET TV. There was a mean 65% mismatch between the FMISO and FDG TVs obtained before and during CRT. FLT TVs corresponded better with the FDG TVs (25% mismatch before and 56% during CRT). During CRT, on average 61% of the mean FDG TV (7 cc) overlapped with the baseline mean TV (15.5 cc) (n=15). For FLT, the TV overlap was 49% (n=5) and for FMISO only 20% of the TV during CRT remained inside the contour at baseline (n=10).
  
  
  CONCLUSIONS
  FDG, FLT and FMISO-PET reflect different functional characteristics that change during CRT in rectal cancer. FLT and FDG show good spatial correspondence, while FMISO seems less reliable due to the non-specific FMISO uptake in normoxic tissue and tracer diffusion through the bowel wall. FDG and FLT-PET/CT imaging seem most appropriate to integrate in preoperative RT for rectal cancer.
authors.affiliation: Leuven Cancer Institute, Radiation Oncology, University Hospital Leuven, Leuven, Belgium.
authors.forename: Sarah
authors.initials: S
authors.lastname: Roels
authors.forename: Pieter
authors.initials: P
authors.lastname: Slagmolen
authors.forename: Johan
authors.initials: J
authors.lastname: Nuyts
authors.forename: John A
authors.initials: JA
authors.lastname: Lee
authors.forename: Dirk
authors.initials: D
authors.lastname: Loeckx
authors.forename: Frederik
authors.initials: F
authors.lastname: Maes
authors.forename: Sigrid
authors.initials: S
authors.lastname: Stroobants
authors.forename: Freddy
authors.initials: F
authors.lastname: Penninckx
authors.forename: Karin
authors.initials: K
authors.lastname: Haustermans
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000627:therapeutic use; D015687:Cell Hypoxia; D003131:Combined Modality Therapy; D015224:Dideoxynucleosides; D019788:Fluorodeoxyglucose F18; D005472:Fluorouracil / Q000627:therapeutic use; D006801:Humans; D008920:Misonidazole / Q000031:analogs & derivatives*; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D012004:Rectal Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden
chemical_list: D000964:Antimetabolites, Antineoplastic; D015224:Dideoxynucleosides; D019275:Radiopharmaceuticals; C031843:fluoromisonidazole; D019788:Fluorodeoxyglucose F18; D008920:Misonidazole; D005472:Fluorouracil