title: MR vs CT imaging: low rectal cancer tumour delineation for three-dimensional conformal radiotherapy.
abstract: Modern three-dimentional radiotherapy is based upon CT. For rectal cancer, this relies upon target definition on CT, which is not the optimal imaging modality. The major limitation of CT is its low inherent contrast resolution. Targets defined by MRI could facilitate smaller, more accurate, tumour volumes than CT. Our study reviewed imaging and planning data for 10 patients with locally advanced low rectal cancer (defined as < 6 cm from the anal verge on digital examination). Tumour volume and location were compared for sagittal pre-treatment MRI and planning CT. CT consistently overestimated all tumour radiological parameters. Estimates of tumour volume, tumour length and height of proximal tumour from the anal verge were larger on planning CT than on MRI (p < 0.05). Tumour volumes defined on MRI are smaller, shorter and more distal from the anal sphincter than CT-based volumes. For radiotherapy planning, this may result in smaller treatment volumes, which could lead to a reduction in dose to organs at risk and facilitate dose escalation.
authors.affiliation: Department of Clinical Oncology, Royal Marsden Hospital, Sutton, Surrey SM2 5PT. brian.oneill@slh.ie
authors.forename: B D P
authors.initials: BD
authors.lastname: O'Neill
authors.forename: G
authors.initials: G
authors.lastname: Salerno
authors.forename: K
authors.initials: K
authors.lastname: Thomas
authors.forename: D M
authors.initials: DM
authors.lastname: Tait
authors.forename: G
authors.initials: G
authors.lastname: Brown
mesh_terms: D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging / Q000379:methods; D016684:Prone Position; D011446:Prospective Studies; D011829:Radiation Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal; D012004:Rectal Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000532:radiotherapy; D016683:Supine Position; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden