SP-0278: No bridge too far
Radiotherapy and Oncology
Purpose/Objective: To compare the maximum target 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 Materials and Methods: All patients with locally advanced cervical cancer treated with radiochemotherapy and IGABT between 09/2012-05/2013 were included in this study. T2weighted MRI (1.5 tesla), TRUS and CT were performed before (MRI
... rmed before (MRI preBT , TRUS preBT ) and / or after (MRI BT , TRUS BT and CT BT ) insertion of the applicator. 3D TRUS image acquisition was done with a customized US stepper device and software. The target was defined on 3D image sequences acquired with different imaging modalities by one blinded observer, in accordance to the GEC-ESTRO recommendations for MRIbased target volume delineation, as the complete cervical mass including the tumour, any suspicious areas of parametrial involvement and the normal cervical stroma. Maximum target 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 MRI BT as reference, and a paired t-test were calculated. Results: Images from 21 patients (FIGO IB: 3, IIB: 11, IIIB: 5, IVB: 2) were available for analysis. The mean difference in maximum target width of TRUS BT, TRUS preBT, MRI preBT, CT BT to MRI BT was 0.5mm ±5.5 (n.s.), -1.7mm ±5.7 (n.s.), 0.0mm ±5.7 (n.s.) and 12.9mm ±6.1 (p < 0.001) (figure 1). The mean difference in maximum target thickness of TRUS BT, TRUS preBT, MRI preBT, CT BT to MRI BT was -3.5mm ±5.5 (p=0.012), -7.6mm ±4.3 (p <0.001), 0.5mm ±6.4 (n.s.) and 11.8mm ±6.3 (p < 0.001). Mean scores of image quality of the target volume was 2.9 for TRUS preBT , 2.3 for TRUS BT , 2.9 for MRI preBT , 2.7 for MRI BT and 2.1 for CT BT . Conclusions: TRUS seems to be superior to CT for assessment of the target volume in IGABT of cervical cancer as it yields systematically smaller deviations from the gold standard T2weighted MRI, with reasonable image quality. Differences of TRUS target thickness might likely be related to differences in image slice orientation and compression of the target volume by the TRUS probe before insertion of the brachytherapy applicator.