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

Table 2. Main parameters of the uRT‑506c platform
Feature Content
Layout Integrated design, diagnostic 16-row spiral
CT, and linear accelerator co-bed coaxial
design
CT aperture 70 cm diameter
The angle of rotation of −362° – 182° and maximum rotation speed
the accelerator frame of 7°/s
Beams 6 MV (FF/FFF) X-ray
Dose rate 25 – 600 MU/min (FF), 75 – 1400 MU/min
(FFF)
Multi-leave collimators 1.0 cm×20 pair, 0.5 cm×40 pair, velocity of
the lobes 2.5 cm/s
The radiation field 40×40 cm 2
Radiotherapy equipment 3D-CRT, IMRT, uARC
Figure 4. United Imaging’s uRT-Linac 506c
Imaging system MV CBCT, kV FBCT
the entire process, from simulation to treatment, to be Abbreviations: 3D-CRT: Three-dimensional conformal radiotherapy;
performed on a single unit. CBCT: Cone-beam computed tomography; CT: Computed
tomography; FBCT: Fan-beam computed tomography; FF: Flattened
Compared to the commonly used kV CBCT in IGRT, filtered; FFF: Flattening filter-free; IMRT: Intensity-modulated
the spiral kV fan-beam CT (FBCT) on the uRT-Linac radiation therapy.
506c is minimally influenced by photon scatter, resulting
in a significant reduction of artifacts and improved overall scanning range, making it particularly well-suited for
image consistency. The FBCT enables layer-by-layer patients with thoracoabdominal tumors.
comparisons between the patient’s anatomical structure It is crucial to acknowledge that during intervals
and the planning CT, providing robust support for adaptive between patient fractions, certain non-rigid alterations in
replanning and effectively mitigating errors caused by anatomical structure may occur, which cannot be corrected
anatomical changes between treatment fractions. by simply translating the treatment couch. Consequently,

The uRT-Linac 506c demonstrates exceptional re-evaluating the ART plan becomes especially critical in
performance in terms of dosimetric accuracy and these conditions. Previous studies confirm that CT-guided
treatment efficiency, as evidenced by the specific machine ART optimizes dose distribution, reduces normal tissue
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parameters, as shown in Table 2. The accelerator gantry exposure, and mitigates side effects. Sara et al. conducted
of the uRT-Linac 506c has an extensive rotation angle a prospective cohort study of 50 locally advanced NSCLC
range, from −362° to 182°, allowing full circular scans patients, with weekly CT replanning based on tumor
to be initiated from any position. This feature proves regression. After a median follow-up of 20.5 months, the
particularly advantageous for treating lesions located CTV decreased by 42%, and grade ≥3 toxicity was 2% in
on the posterior side of the body. Moreover, this device the ART group versus 4% in the non-ART group. Schiff
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incorporates a high-quality CT system that surpasses et al. reported a single-arm prospective study of 40
CBCT in terms of image quality. FBCT exhibits locally advanced pancreatic cancer patients treated with
minimal susceptibility to scattered radiation, resulting CT-guided adaptive stereotactic body radiation therapy
in an improved contrast-to-noise ratio and enhanced (SBRT), demonstrating superior dosimetry compared to
low-contrast detection capability. Furthermore, kV non-adaptive SBRT.
FBCT demonstrates superior accuracy in soft tissue 4. MRI-guided adaptive RT
registration. According to a study by Morrow et al.,
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FBCT significantly reduces uncertainties associated Compared to CBCT and CT, MRI possesses the advantages
with soft tissue registration during IGRT procedures, of superior soft tissue resolution and radiation-free safety,
especially for the treatment of prostate and gynecological thereby providing reliable imaging evidence for adaptive
tumors due to its superior image quality. In comparison planning in ART. During ART treatment, real-time
with the kV CBCT, FBCT excels in visualizing soft- MRI tracking enables dynamic monitoring of tumor
tissue structures while providing faster scanning speed, and OARs changes, effectively mitigating errors arising
improving motion artifact control, and widening from positional variations and organ deformations. By

Volume 3 Issue 3 (2025) 8 doi: 10.36922/ARNM025110012