title: The utility of multimodality imaging with CT and MRI in defining rectal tumour volumes for radiotherapy treatment planning: a pilot study.
abstract: OBJECTIVE
  This study compares the volumetric and spatial relationships of gross tumour volume (GTV) derived from CT (CT-GTV) and GTV derived from MRI (MR-GTV) to determine the utility of multi-modality imaging for radiotherapy treatment planning in rectal cancer.
  
  
  METHODS
  Fifteen patients with T3 rectal cancer were accrued over 18 months. The male : female ratio was 2:1. The average age was 60.3 years (range 38-79). All patients underwent a diagnostic MRI and CT and MRI simulation. Data sets were co-registered. A site specialised diagnostic radiologist contoured all volumes in consultation with a radiation oncologist. CT-GTV was contoured while blinded to MR data sets. MR-GTV was contoured independently 2-4 weeks later whilst blinded to its respective CT-GTV data. Tumour volumes were analysed for three anatomical subregions (sigmoid, rectal and anal). Reference points on tumour volumes were used for spatial comparison and analysis.
  
  
  RESULTS
  The mean CT-GTV/MR-GTV ratio was 1.2 (range 0.5-2.9). The tumour volume ratios for the rectal subregion were well correlated. CT-GTV provided adequate spatial coverage of tumour in reference to MR-GTV with the average mean discrepancy of 0.12 (range -0.08-0.38) or a maximum discrepancy of <0.4 cm (1.54 standard deviation). CT-GTV coverage was inadequate for tumours with MRI evidence of anal and sigmoid invasion.
  
  
  CONCLUSIONS
  Conventional simulation CT imaging provided a reasonable estimate of the GTV. Multi-modality imaging with staging MRI can assist target volume definition where there is involvement of the sigmoid and anorectal region and avoid geographic misses. The role of a simulation MRI may aid in this process but remains investigational.
authors.affiliation: Radiation Oncology Centre, Austin Health, Heidelberg West Radiology, Austin Health, Heidelberg, Victoria 3081, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Tan
authors.forename: D
authors.initials: D
authors.lastname: Lim Joon
authors.forename: G
authors.initials: G
authors.lastname: Fitt
authors.forename: M
authors.initials: M
authors.lastname: Wada
authors.forename: M
authors.initials: M
authors.lastname: Lim Joon
authors.forename: A
authors.initials: A
authors.lastname: Mercuri
authors.forename: M
authors.initials: M
authors.lastname: Marr
authors.forename: M
authors.initials: M
authors.lastname: Chao
authors.forename: V
authors.initials: V
authors.lastname: Khoo
mesh_terms: D000328:Adult; D000368:Aged; D003287:Contrast Media; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D012007:Rectum / Q000000981:diagnostic imaging / Q000473:pathology; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden
chemical_list: D003287:Contrast Media