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. 2025 Jan-Dec:24:15330338251366729.
doi: 10.1177/15330338251366729. Epub 2025 Aug 6.

Evaluation of Concomitant Imaging Dose in 4D-CBCT Guided Thoracic Radiotherapy

Wu Jianan  1 , Sang Yong  1 , Li Zhangmin  2 , Liang Ying  1 , Zhao Man  1 , Hu Yuchao  1 , Jia Yajun  1
Affiliations

Evaluation of Concomitant Imaging Dose in 4D-CBCT Guided Thoracic Radiotherapy

Wu Jianan et al. Technol Cancer Res Treat. 2025 Jan-Dec.

Abstract

IntroductionThis retrospective study evaluated the imaging dose of 4D-CBCT in patients treated with thoracic radiotherapy.MethodsA geometric model of a 4D-CBCT system was built for Monte Carlo (MC) calculations. Percentage depth dose (PDD) and profiles of the system were measured and compared with MC calculations to verify the model. Eight lung cancer patients were retrospectively selected for 4D-CBCT imaging dose assessment. For each patient, the imaging dose was calculated using the CBCT log file, simulating CT and the MC model. Organ at risk (OAR) dose parameters from the imaging dose were calculated, and the effect of the imaging dose on OAR dose parameters when the imaging dose was added to the treatment dose was analyzed.ResultsDeviations between MC calculations and measurements for PDD and profiles were within 1.1% and 5%, respectively. For a pre-treatment 4D-CBCT scan, the mean lung and heart doses were 9.5 ± 1.4 mGy (mean value ± standard deviation, hereafter the same) and 9.7 ± 1.4 mGy, and the maximum spinal cord, esophagus and ribs doses were 17.6 ± 4.2 mGy, 17.1 ± 3.3 mGy and 37.8 ± 5.3 mGy, respectively. For an in-treatment 4D-CBCT scan, the dose parameters were 5.6 ± 1.8 mGy, 5.6 ± 1.5 mGy, 10.3 ± 3.5 mGy, 10.3 ± 4.3 mGy and 22.4 ± 5.3 mGy, respectively. The OAR dose parameters for in-treatment 4D-CBCT scans showed a relatively strong linear relationship with beam MU and number of frames. For patients receiving 5-fraction treatments and one pre-treatment and one in-treatment 4D-CBCT for each fraction, the increases in lung V20, lung V5, mean lung and heart doses, maximum spinal cord, esophagus and ribs doses were 0.04 ± 0.03%, 0.29 ± 0.23%, 76.3 ± 14.4 mGy, 76.5 ± 12.0 mGy, 76.3 ± 20.2 mGy, 70.5 ± 13.1 mGy and 101.2 ± 20.5 mGy, respectively. The increase in OAR dose parameters was proportional to the number of fractions.ConclusionThe imaging dose of pre-treatment and in-treatment 4D-CBCT was calculated using a validated MC model. For 5-fraction treatments, the imaging dose will likely have minimal clinical impact on OAR dose parameters.

Keywords: 4D-CBCT; Monte Carlo method; imaging dose; in-treatment 4D-CBCT; thoracic radiotherapy.

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Conflict of interest statement

Declaration of Conflicting InterestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
MC Calculated and Measured Percentage Depth Dose (PDD) Curves of the 4D-CBCT System Using S20 and F1. the top Panel Shows the Normalized PDD Curves, and the Bottom Panel Shows Their Percentage Differences.
Figure 2.
Figure 2.
MC Calculated and Measured (a) Cross-Line and (b) In-Line Profiles of the 4D-CBCT System Using S20 and F1. The Top Panels Show the Normalized Profile Curves, and the Bottom Panels Shows Their Percentage Differences.
Figure 3.
Figure 3.
Dose Distribution on a Patient's CT from a Single (a) pre-Treatment and (b) in-Treatment 4D-CBCT Scan, Each Showing the Transverse, Sagittal and Coronal Planes from Left to Right. the red Patch Indicates the Treatment Target.
Figure 4.
Figure 4.
Dose parameters of the OARs from a Single Pre-treatment or In-Treatment 4D-CBCT Scan.
Figure 5.
Figure 5.
Relationship of Number of kV Frames Acquired with in-Treatment Scan as a Function of Treatment Beam MUs.
Figure 6.
Figure 6.
Relationship of Imaging Dose Parameters of the OARs from In-Treatment Scans as a Function of Beam MUs.
Figure 7.
Figure 7.
Relationship of Imaging Dose Parameters of the OARs from in-Treatment Scans as a Function of Number of kV Frames Acquired.
Figure 8.
Figure 8.
The Statistical Distributions of the Increases in OAR Dose Parameters from 5 Fractions of Pre-treatment and In-treatment 4D-CBCT Scans.
Figure 9.
Figure 9.
The Increase in OAR Dose Parameters from Pre-Treatment and In-Treatment 4D-CBCT Scans Per Treatment as a Function of the Number of Treatment Fractions.
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