A review of cone-beam CT applications for adaptive radiotherapy of prostate cancer

•Adaptive radiotherapy should include both, image-guided and dose-guided procedures.•Rigid registrations are accurate for adaptive procedures for prostate only region.•For region of prostate and seminal vesicles, non-rigid registrations are needed.•The quality of CBCT is one of most important variables affecting adaptation accuracy. The aim of this study was to systematize the information on adaptive radiotherapy based on cone-beam computed tomography (CBCT) imaging for patients with prostate cancers including the prostate gland only, or the prostate gland and seminal vesicles region. A systematic literature search was carried out using the PubMed engine, based upon the following terms: adaptive radiotherapy, intensity modulated radiotherapy, volumetric modulated arc therapy and image-guided and dose-guided radiotherapy. Overall, 58 relevant studies were included: 31 about on-line strategies of adaptation, 6 about off-line strategies, and 21 that highlighted the technical aspects of CBCT usage. The off-line strategies provide a statistical prediction for each individual patient for the rest of treatment. The on-line strategies aim to resolve the potential disagreements between a planned and delivered dose directly before the specific fraction. Both strategies need information about the movements of the irradiated region relative to the target from treatment planning and the dose delivered relative to the planned dose. Quality of CBCT is very important for the accuracy of the adaptation procedures. While the errors caused by the insufficient quality of anatomy visualisation with CBCT are currently minimized, there are still problems with the proper dose computation. The most accurate methods are able to minimize the calculation error to 3%. CBCT plays a significant role in each step of adaptive radiation therapy of prostate cancers, starting from registration procedures through setting an appropriate CTV-to-PTV margin to fraction dose recalculations, and its cumulation/monitoring relative to the planned dose.