Page 74 - ARNM-2-4

Advances in Radiotherapy
& Nuclear Medicine Comparison of online ATP versus offline ATS plans

Committee of our hospital (No: SDTHEC2024007028, In both groups, the OAR contouring included the bladder,
date: July 22 2024), and informed consent was obtained rectum, left and right femoral heads, and the small bowel
nd
from all the patients and their families. because these structures are particularly sensitive and
require careful monitoring to avoid excessive radiation
2.2. Imaging studies during the treatment exposure.
2.2.1. Computed tomography (CT) simulation
2.4. Treatment planning
All patients were positioned supine with their hands
crossed above their heads and stabilized with a customized After CT was performed for localization, the acquired
vacuum bag. Respiratory motion was controlled by images were imported into the Monaco TPS for designing
applying an abdominal compression belt, and the the plan. Intensity-modulated radiation therapy (IMRT)
placement and compression intensity of the belt were was delivered using gantry angles of 180°, 130°, 80°, 30°,
documented. The patients consumed 500 mL of water 330°, 280°, and 230°, with a collimator angle of 0° and a
before the scan. Standard axial enhancement scans were maximum dose rate of 400 MU/min. Approximately 95%
obtained using a large-aperture simulation (CT; 16-slice of the CTV was administered 100% of the prescribed dose
Brilliance Big Bore; Philips Medical Systems, Amsterdam, of 50 Gy in 25 fractions over 5 weeks. Dose constraints
The Netherlands), with a 3-mm slice thickness and a 3-mm for the remaining OARs were established on the basis of
gap between slices. relevant international standards.

2.2.2. Daily MRI during radiotherapy 2.5. Online ATP and offline ATS workflows
All patients underwent an online MRI before treatment The online adaptive radiotherapy process involved
using the following 2D-TSE/T2WI scanning parameters: obtaining a real-time MRI before each treatment session
TR/TE, 1535 ms/278 ms; FOV, 400 × 400 × 300 mm³; matrix (Figure 1). Subsequently, this MRI was rigidly aligned with
size, 268 × 267 × 300; and voxel size, 1.5 × 1.5 × 2 mm³. the planning CT using Monaco TPS. An online adaptive
MR images from the first three treatment sessions of treatment plan was generated using the ATP workflow.
each patient were analyzed. Using standardized imaging During the online adaptive planning process, the CTV and
parameters, we ensured that the images were comparable OAR motions were monitored using a balanced, steady-
across patients and treatment sessions. Before each state, and free precession sequence. For offline adaptive
treatment session, all patients were required to follow the planning, the MR images acquired during the daily
same bladder preparation protocol as that used during the treatment were used. The corresponding CTV and OAR
initial CT simulation. were contoured within Monaco TPS, and the treatment
plan was designed using the ATS workflow. The plan
2.3. CTV and OAR contouring design requirements and OAR dose constraints for the
Two radiation oncologists used the Monaco treatment online ATP and offline ATS plans were consistent with
planning system (TPS) (Elekta, Stockholm, Sweden) to relevant international standards. Online ATP plans were
contour the corresponding CTV and OAR on the patient’s approved before the plan was implemented, while offline
daily MR images and simulation CT. Patients were ATS plans were approved after they were developed offline
divided into the following two groups based on whether by a physicist, clinical radiotherapist, and senior physicist.
they had undergone surgery: the radical radiotherapy 2.6. Statistical analysis
group and the post-operative radiotherapy group. In the
radical radiotherapy group, the CTV included the primary Statistical Package for the Social Sciences (version 25.0;
tumor, cervix, uterus, proximal vagina (based on the area IBM Corporation, Armonk, New York, USA) was used to
of tumor infiltration), paracervical tissues, lymph nodes perform statistical analysis of the dosimetric parameters of
(including the external iliac, internal iliac, occlusive CTV, PTV, and OAR, which have been expressed as means
foramen, presacral, and common iliac lymph nodes), and ± standard deviations. The Shapiro-Wilk test was used to
para-aortic and inguinal lymphatic drainage areas (based assess the normality of the data distribution. The Wilcoxon
on the patient’s situation). However, in the post-operative signed-rank test was used, and statistical significance was
radiotherapy group, only the vaginal stump, paracervical set at 0.05.
tissue, and associated lymph nodes were contoured. The 3. Results
PTV was created by expanding the CTV outward by 0.5 cm
to account for potential errors and organ motion during Twenty-five patients with cervical cancer were included
treatment. This margin ensured adequate coverage of the in this study. The patient and disease characteristics are
target area despite any slight movements or uncertainties. summarized in Table 1. The mean age of the patients was

Volume 2 Issue 4 (2024) 3 doi: 10.36922/arnm.4919