Page 15 - ARNM-3-3

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

exhibited high accuracy, establishing a robust foundation The PTV was reduced by approximately 33%, and ART
for ART. significantly lowered lung dose (mean lung dose: 14.6 Gy
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In terms of treatment duration, CBCT-guided ART vs. 12.6 Gy). Multiple studies have demonstrated that ART
possesses a significant advantage due to the consistent can improve dose delivery to target volumes in cervical
alignment of CBCT images with the isocenter of the cancer while effectively reducing radiation exposure to
treatment couch, eliminating the need for repositioning. OARs such as the bladder and rectum, with high efficiency
A study conducted on prostate cancer patients reported an and time-saving advantages. In a Phase II prospective
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average time of only 17.5 ± 3.2 min from patient positioning study by Wang et al., 17 postoperative endometrial or
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to CBCT verification. Another study utilizing the Ethos cervical cancer patients underwent daily CBCT-guided
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linear accelerator for rectal cancer patients demonstrated online ART. Vaginal target coverage improved by 7%, with
an average treatment time of approximately 26 min. The no grade 3 – 4 gastrointestinal or genitourinary toxicities
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required time for target delineation varied depending on reported. Branco et al. conducted a comparative analysis
whether modifications to system-generated contours were of cumulative doses to target volumes and OARs between
necessary, with an average of 4 min needed when assessing ART and non-ART groups in a study of 15 cervical cancer
or adjusting bladder and rectum contours generated by the patients. The results indicated that the ART group achieved
system and an average of 9 min needed when adjustments a significant reduction in D50% for both the bladder and
to target contours were required. rectum. Another study evaluated nearly 150 ART sessions
across 13 patients with cervical and rectal cancers. The
CBCT-guided ART has shown significant dosimetric mean clinical workflow time for cervical cancer ART was
benefits in several cancers, such as lung cancer, cervical approximately 24 min. V95% coverage increased by an
cancer, and endometrial cancer. Optimizing CTV margins, average of 9.2%. D2cc values for the bladder, bowel, and
either without expansion or with margin reduction using rectum were significantly reduced. 51
ART, not only enhances target coverage but also diminishes
radiation exposure to adjacent normal tissues. This 3. Computed tomography-guided
approach ensures treatment precision while minimizing adaptive RT
adverse effects. Online ART has the potential to reduce
toxicity in rectal cancer patients by allowing smaller PTV Computed tomography imaging provides high-resolution
margins around the CTV. A CBCT-based ART study images, facilitating precise delineation of tumor target
for rectal cancer evaluated the time requirements, plan areas and OARs for the accurate development of RT plans
quality, target coverage, and patient compliance. The study in ART. However, a practical challenge arises from the
recruited 12 rectal cancer patients, all of whom received spatial misalignment between the CT equipment and the
preoperative RT with a regimen of five fractions at 5 Gy accelerator, mainly resulting in misalignment between
each. The online adaptation procedure began with CBCT the CT isocenter and the treatment couch’s center point. In
acquisition, utilizing AI for target delineation. Second and clinical practice, patients need to be repositioned frequently
third CBCTs were performed before and after treatment, between the CT scanner and the treatment couch. Failure
respectively, to verify CTV coverage in the new plan. to achieve precise alignment of isocenters may lead to off-
Following quality assessment, the RT plans were delivered target dose delivery. Furthermore, adjusting the isocenter is
using volumetric modulated arc therapy (VMAT). In not only time-consuming but also prolongs ART treatment
the treatment of rectal cancer, online ART demonstrates duration, potentially compromising patient experience.
significant advantages. On average, the time required at the Figure 4 shows United Imaging’s uRT-Linac 506c. Unlike
treatment machine is 34 min. The processes of acquiring traditional sliding rail CT designs, which utilize moving
a CBCT, evaluating and adjusting the contours, creating a gantries and rotating axes at the top of the scanning bed,
new plan, and verifying the CTV on the CBCT scan take the uRT-Linac 506c integrates a diagnostic-grade spiral CT
an average of 20 min. When including treatment delivery system behind the C-arm gantry of the linear accelerator.
and post-treatment verification, the total time is 26 min. This system supports enhanced CT scanning, facilitating
Online ART exhibits excellent performance in terms of precise target delineation and adaptive plan modification.
plan quality, target coverage, and patient compliance. In addition, the uRT-Linac 506c is equipped with CBCT
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Møller et al. conducted a prospective cohort study of functionality, enabling real-time imaging and treatment
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233 patients with stage IA-IV non-small cell lung cancer adaptation. By moving the scanning bed longitudinally,
(NSCLC) and small cell lung cancer, using daily CBCT to patients can easily enter the scanner, achieving seamless
monitor anatomical changes. Among 63 patients requiring integration of enhanced CT scanning, CBCT imaging,
plan adjustments, 75% addressed tumor underdosing. and treatment, as displayed in Figure 4. This design allows

Volume 3 Issue 3 (2025) 7 doi: 10.36922/ARNM025110012