Review of cone beam computed tomography based online adaptive radiotherapy: current trend and future direction

Abstract

Adaptive radiotherapy (ART) was introduced in the late 1990s to improve the accuracy and efficiency of therapy and minimize radiation-induced toxicities. ART combines multiple tools for imaging, assessing the need for adaptation, treatment planning, quality assurance, and has been utilized to monitor inter- or intra-fraction anatomical variations of the target and organs-at-risk (OARs). Ethos™ (Varian Medical Systems, Palo Alto, CA), a cone beam computed tomography (CBCT) based radiotherapy treatment system that uses artificial intelligence (AI) and machine learning to perform ART, was introduced in 2020. Since then, numerous studies have been done to examine the potential benefits of Ethos™ CBCT-guided ART compared to non-adaptive radiotherapy. This review will explore the current trends of Ethos™, including improved CBCT image quality, a feasible clinical workflow, daily automated contouring and treatment planning, and motion management. Nevertheless, evidence of clinical improvements with the use of Ethos™ are limited and is currently under investigation via clinical trials.

Evaluation of Motion Artifact Correction Technique for Cone-Beam Computed Tomography Image Considering Blood Vessel Geometry

“…However, the acquisition of qualified CBCT images can lead to a more accurate diagnosis and appropriate treatment. Therefore, various attempts are being made to reduce distortion caused by the patient's movement and respiration and improve the quality of CBCT images [28][29][30][31][32][33]. CBCT images are very important images that provide direct information for catheter intervention.…”

Fractionation versus Adaptation for Compensation of Target Volume Changes during Online Adaptive Radiotherapy for Bladder Cancer: Answers from a Prospective Registry

“…In addition, adaptation times varied over a wider range in this study as both VMAT and 12-field IMRT were used. With 12-field IMRT adaptation, times can be reduced by about 10 min allowing less time for intra-fraction deformations [28]. This study did not allow a validated prediction of the individual minimum PTV margin for a bladder cancer patient, which was sufficient to compensate for intra-fraction deformation during dose adaptation so farhowever, it introduced worstcase dose accumulation with limited redistribution of cold spots to predict the dosimetric outcome of a whole treatment series using the first few fractions of the series, and to monitor the effectiveness of the delivered dose fractions thus far from the dose-volume histograms for the CTV or organs at risk of these fractions alone without the recourse to DIR-based dose accumulation.…”

“…The adapted plan was optimized on the anatomy of the day according to the initially defined clinical goals (CTV: D 99% ≥ 98%, Bladder [focal therapy]: D mean ≤ 55%, and Rectum: V 30 % ≤ 35%). In four of the treatment series, a volumetric modulated arc treatment technique was chosen, which takes about 13 min of planning calculation time and in the remaining time, a 12-fixed field intensity-modulated radiotherapy technique was chosen that took about 3, 4 min for plan optimization [28].…”

Adaptation Time as a Determinant of the Dosimetric Effectiveness of Online Adaptive Radiotherapy for Bladder Cancer

“…From this study, it follows that adaptation times in the upper tercile of observed values above 20.8 min are critical and should be minimized. One option to speed up the process is the use of 9 or 12 field IMRT instead of VMAT plans, with optimization times of about 3-4 min instead of 13-14 min [42]. In addition, each additional imaging requires contouring of the organs at risk and of the target volume.…”