Evaluation of a mobile C-arm cone-beam CT in interstitial high-dose-rate prostate brachytherapy treatment planning

Introduction The aim of this study was to evaluate the suitability of using cone-beam computed tomography (CBCT) obtained with a mobile C-arm X-ray fluoroscopy unit as a single modality for planning of high-dose-rate (HDR) prostate brachytherapy treatments. Methods The feasibility of using CBCT images obtained using a Siemens Arcadis Orbic 3D mobile C-arm was evaluated. A retrospective clinical study was undertaken of six participants undergoing HDR prostate brachytherapy. Plans generated using images from a Toshiba Aquilion One LB CT were compared with those generated using CBCT images. After rigid spatial registration, the plans were compared based on various parameters such as dose-volume histograms, overlap quantities and metrics, and dose constraints. Results Provided they were within the limited field of view, the brachytherapy catheters and fiducial markers were clearly visible in the CBCT images and thus, localisable and identifiable in the treatment planning process. The Siemens CBCT underestimated CT numbers leading to poorer tissue contrast which exacerbated the difficulties in delineation of the target tumour and the surrounding organs at risk. Between CT- and CBCT-based plans, the mean difference of CTV-D-90 was 1.58 Gy, CTV-V-100 was 12.13%, rectum-V-80 was 0.06% and urethra-V-120 was -0.70%. Conclusion It was not feasible to solely utilise the Siemens Arcadis Orbic 3D for HDR prostate brachytherapy treatment planning due to suboptimal organ delineation. However, the methods in this study could be used to evaluate other mobile CBCT imaging devices for feasibility in HDR brachytherapy treatment planning since the results indicated that it may not be necessary to have standard quality CT images for treatment planning.