title: Transrectal ultrasound for image-guided adaptive brachytherapy in cervix cancer - An alternative to MRI for target definition?
abstract: To compare the maximum high risk clinical target volume (CTVHR) dimensions and image quality between magnetic resonance imaging (MRI), transrectal ultrasound (TRUS) and computed tomography (CT) in image guided adaptive brachytherapy (IGABT) of locally advanced cervical cancer.
  
  
  
  All patients with locally advanced cervical cancer treated with radiochemotherapy and IGABT between 09/2012-05/2013 were included in this study. T2-weighted MRI (1.5 tesla), TRUS and CT were performed before (MRIpreBT, TRUSpreBT) and/or after (MRIBT, TRUSBTand CTBT) insertion of the applicator. 3D TRUS image acquisition was done with a customized US stepper device and software. The HR CTV was defined on 3D image sequences acquired with different imaging modalities by one blinded observer, in accordance to the GEC-ESTRO recommendations for MRI-based target volume delineation, as the complete cervical mass including the tumour, any suspicious areas of parametrial involvement and the normal cervical stroma. Maximum HR CTV width and thickness were measured on transversal planes. Image quality was classified using the following scoring system: Grade 0: not depicted, Grade 1: inability to discriminate, margin not recognizable, Grade 2: fair discrimination, margin indistinct, Grade 3: excellent discrimination, margin distinct. Descriptive statistics, mean differences between the groups, with MRIBTas reference, and a paired t-test were calculated.
  
  
  
  Images from 19 patients (FIGO IB: 3, IIB: 9, IIIB: 5, IVB: 2) were available for analysis. The mean difference in maximum HR CTV width of TRUSBT,TRUSpreBT,MRIpreBT,CTBTto MRIBTwas 0.0mm±4.7 (n.s.), -1.1mm±5.6 (n.s.), 0.7mm±6.4 (n.s.) and 13.8mm±6.7 (p<0.001). The mean difference in maximum HR CTV thickness of TRUSBT,TRUSpreBT,MRIpreBT,CTBTto MRIBTwas -3.4mm±5.9 (p=0.037), -3.4mm±4.2 (p<0.001), 2.0mm±6.1 (n.s.) and 13.9mm±6.3 (p<0.001). Mean scores of image quality of the target volume was 2.9 for TRUSpreBT, 2.3 for TRUSBT, 2.9 for MRIpreBT, 2.7 for MRIBTand 2.1 for CTBT.
  
  
  
  For the assessment of the HR CTV in IGABT of cervical cancer, TRUS is within the intraobserver variability of MRI. TRUS is superior to CT as it yields systematically smaller deviations from MRI, with good to excellent image quality. Small differences of TRUS HR CTV thickness are likely related to differences in image slice orientation and compression of the cervix by the TRUS probe before insertion of the brachytherapy applicator.
authors.affiliation: Department of Radiation Oncology, Comprehensive Cancer Center, Medical University of Vienna, Austria. Electronic address: maximilian.schmid@akhwien.at.
authors.forename: Maximilian P
authors.initials: MP
authors.lastname: Schmid
authors.affiliation: Department of Radiation Oncology, Comprehensive Cancer Center, Medical University of Vienna, Austria.
authors.forename: Nicole
authors.initials: N
authors.lastname: Nesvacil
authors.affiliation: Department of Radiation Oncology, Comprehensive Cancer Center, Medical University of Vienna, Austria; Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Austria.
authors.forename: Richard
authors.initials: R
authors.lastname: Pötter
authors.affiliation: Austrian Center for Medical Innovation and Technology - ACMIT, Wiener Neustadt, Austria.
authors.forename: Gernot
authors.initials: G
authors.lastname: Kronreif
authors.affiliation: Department of Radiation Oncology, Comprehensive Cancer Center, Medical University of Vienna, Austria; Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University of Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Kirisits
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D059248:Chemoradiotherapy / Q000379:methods; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D009367:Neoplasm Staging; D015588:Observer Variation; D058958:Organs at Risk; D016037:Single-Blind Method; D014057:Tomography, X-Ray Computed / Q000379:methods; D018084:Ultrasonography, Interventional / Q000379:methods; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy* / Q000628:therapy
keywords: Cervix cancer; Image-guided adaptive brachytherapy; MRI; Radiotherapy; Transrectal ultrasound