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. 2023 Apr;24(4):e13865.
doi: 10.1002/acm2.13865. Epub 2022 Dec 26.

Commissioning and performance evaluation of commercially available mobile imager for image guided total body irradiation

Tetsu Nakaichi  1 , Hiroyuki Okamoto  1 , Mitsuhiro Kon  1   2 , Kazuki Takaso  2 , Ako Aikawa  2 , Satoshi Nakamura  1 , Kotaro Ijima  1 , Takahito Chiba  1 , Hiroki Nakayama  1   3 , Mihiro Takemori  1   3 , Shohei Mikasa  1 , Kyohei Fujii  4 , Yuka Urago  1   3 , Tomonori Goka  2 , Yuri Shimizu  5 , Hiroshi Igaki  5
Affiliations

Commissioning and performance evaluation of commercially available mobile imager for image guided total body irradiation

Tetsu Nakaichi et al. J Appl Clin Med Phys. 2023 Apr.

Abstract

Background: The setup of lung shield (LS) in total body irradiation (TBI) with the computed radiography (CR) system is a time-consuming task and has not been quantitatively evaluated. The TBI mobile imager (TBI-MI) can solve this problem through real-time monitoring. Therefore, this study aimed to perform commissioning and performance evaluation of TBI-MI to promote its use in clinical practice.

Methods: The source-axis distance in TBI treatment, TBI-MI (CNERGY TBI, Cablon Medical B.V.), and the LS position were set to 400, 450, and 358 cm, respectively. The evaluation items were as follows: accuracy of image scaling and measured displacement error of LS, image quality (linearity, signal-to-noise ratio, and modulation transfer function) using an EPID QC phantom, optimal thresholding to detect intra-fractional motion in the alert function, and the scatter radiation dose from TBI-MI.

Results: The accuracy of image scaling and the difference in measured displacement of the LS was <4 mm in any displacements and directions. The image quality of TBI imager was slightly inferior to the CR image but was visually acceptable in clinical practice. The signal-to-noise ratio was improved at high dose rate. The optimal thresholding value to detect a 10-mm body displacement was determined to be approximately 5.0%. The maximum fraction of scattering radiation to irradiated dose was 1.7% at patient surface.

Conclusion: MI-TBI can quantitatively evaluate LS displacement with acceptable image quality. Furthermore, real-time monitoring with alert function to detect intrafraction patient displacement can contribute to safe TBI treatment.

Keywords: EPID; TBI; in vivo dosimetry; lung shield; mobile imager; real-time monitoring.

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Conflict of interest statement

H. O has a research grant from Item Corporation.

Figures

FIGURE 1
FIGURE 1
Left: a setup geometry of an anthropomorphic RANDO phantom and the LS placed on the dedicated TBI couch; right: an image of RANDO phantom with the LS placed taken by TBI imager and manually outlined the LS (yellow line). RANDO; LS; lung shield
FIGURE 2
FIGURE 2
Images with RANDO phantom using a lung shield obtained by TBI imager. Left: example of an image with the LS displaced 1‐cm posterior from the reference position; right: example of RANDO phantom image acquired with the LS placed at the reference position and manual contouring of the LS
FIGURE 3
FIGURE 3
The image example of EPID QC phantom and the arrangement of physical evaluation items: (1) signal linearity and signal‐to‐noise ratio; (2) spatial resolution (modulation transfer function)
FIGURE 4
FIGURE 4
The arrangement for measuring the scattered radiation dose from the TBI imager. The parallel‐plate ionization chamber at a depth of 0 cm in a 40 cm thick tough water phantom placed on the dedicated couch. Its depth was changed to 0, 2, 5, and 20 cm, and measurements were performed with and without the TBI imager
FIGURE 5
FIGURE 5
The difference of measured displacement for anterior, posterior, superior, and inferior directions from specified displacement (5, 10, and 20 mm) of the LS. LS, lung shield
FIGURE 6
FIGURE 6
The example of EPID QC phantom image acquired with CR and TBI imager. Left side: 70‐MU equivalent image created by summing up 12 TBI imager images irradiated at a dose rate of 300 MU/min, right side: CR image irradiated at 70 MU. CR, computed radiography
FIGURE 7
FIGURE 7
The linearity of changes in the gray level (%) with respect to the copper wedge absorption (%) in each dose level (100, 300, 600 MU/min, 70 MU equivalent, 70 MU with CR image)
FIGURE 8
FIGURE 8
The change in the signal‐to‐noise ratio with respect to the gray level (%) in each dose level (100, 300, 600 MU/min, 70 MU equivalent, and 70 MU with CR image)
FIGURE 9
FIGURE 9
The modulation transfer function with respect to the spatial frequency (linepair/mm) of each dose level (100, 300, 600 MU/min, 70 MU equivalent, and 70 MU with CR image)
FIGURE 10
FIGURE 10
Thresholding values based on LS and RANDO phantom displacements. LS, lung shield. The average thresholding value to detect RANDO phantom displacement was 4.6
FIGURE 11
FIGURE 11
The increasing fraction of scattering radiation dose based on the depth of ionization chamber within tough water phantom due to the presence of TBI imager. The fraction of scatter radiation dose from the TBI imager decreased with increasing the depth of water‐equivalent phantom
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