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Advances in Radiotherapy
& Nuclear Medicine Review of image-guided adaptive radiotherapy

A B C

D E F

Figure 2. Workflow of online ART. (A) Patient positioning; (B) Image registration and fusion of FBCT and planning CT; (C) Automated segmentation
of OARs and propagation of target contours onto FBCT, followed by a thorough review and refinement of the contours; (D) Adapted plan created using
original planning objective, and review adapted and original plan; (E) Repeat FBCT; (F) Deliver treatment.
Abbreviations: ART: Adaptive radiotherapy; CT: Computed tomography; FBCT: Fan-beam computed tomography.

technologies influencing ART include more sophisticated images. To address these challenges and enhance image
imaging modalities combined with advanced AI quality, Varian Medical Systems (Palo Alto, California,
algorithms, as well as treatment planning systems capable USA) introduced iterative CBCT (iCBCT) technology and
®
of rapidly processing imaging data and performing real- developed the Ethos platform, which is an online ART
time plan adjustments; (iii) Real-time ART enables the system based on CBCT guidance. The Ethos® platform
real-time monitoring of anatomical changes in patients not only optimizes CBCT strategies for accurate soft-tissue
during treatment fractions and facilitates online treatment delineation and dose calculation but also incorporates
plan optimization. 37,38 However, this approach encounters HyperSight CBCT technology. 42,43
significant technical challenges that currently limit its The HyperSight technology fully exploits the imaging
practical applications. The workflow of the three-mode advantages of iCBCT, significantly reducing image
ART approach is illustrated in Figure 3. acquisition time to 6 sec while expanding the field of view
Regarding the current clinical application of ART, to 70 cm. In comparison to traditional CBCT, HyperSight
this discussion primarily concentrated on online ART. has made substantial advancements in image contrast,
The successful implementation of online ART heavily uniformity, noise control, and artifact reduction, exhibiting
relies on well-established medical imaging techniques. image quality comparable to planning CT. Currently, the
®
Different imaging modalities possess distinct advantages, Ethos platform has gained widespread application in
disadvantages, and application characteristics. clinical settings, and it has been extensively investigated in
Consequently, the merits, drawbacks, and application numerous related studies.
features of various image-guided ART approaches, A published study utilized the Ethos platform to treat
®
including CT, cone-beam CT (CBCT), and MRI, are five patients with cervical cancer. Before each RT session,
43
summarized and presented in Table 1. the first iCBCT (iCBCT1) image was uploaded onto the
2. CBCT-guided adaptive RT Ethos® simulator. Utilizing iCBCT1 as a reference, the
Ethos simulator automatically generated contours for
®
CBCT is a widely utilized imaging technique in image- key anatomical structures (e.g., bladder, rectum, and small
guided RT (IGRT), characterized by its well-established intestine) and the CTV, without the need for manual
technology and user-friendly operation. 39-41 However, adjustments in the preliminary stage. Subsequently, these
conventional CBCT has limitations in providing clear auto-generated contours were manually adjusted by
visualization of soft tissues, especially when compared physicians when necessary. The findings demonstrated
to contrast-enhanced CT imaging. Moreover, factors that among patients with cervical cancer undergoing RT
such as patient motion during RT, radiation scatter, and postoperatively, 92.3% (346/375) of anatomical structure
image artifacts further compromise the quality of CBCT contours and 92% (230/250) of CTV contours required

Volume 3 Issue 3 (2025) 5 doi: 10.36922/ARNM025110012