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. 2024 Jun;25(6):e14280.
doi: 10.1002/acm2.14280. Epub 2024 Jan 22.

Intra- and inter-fractional variations of tumors with fiducial markers measured using respiratory-correlated computed tomography images for respiratory gated lung stereotactic body radiation therapy

Yuki Manabe  1 , Takehiro Shiinoki  1 , Koya Fujimoto  1 , Kazushi Ueda  1 , Masako Karita  1 , Taiki Ono  1 , Miki Kajima  1 , Hidekazu Tanaka  1
Affiliations

Intra- and inter-fractional variations of tumors with fiducial markers measured using respiratory-correlated computed tomography images for respiratory gated lung stereotactic body radiation therapy

Yuki Manabe et al. J Appl Clin Med Phys. 2024 Jun.

Abstract

Purpose: This study evaluated the intra- and inter-fractional variation of tumors with fiducial markers (FMs), relative to the tumor-FM distance, to establish how close an FM should be inserted for respiratory-gated stereotactic body radiation therapy (RG-SBRT).

Methods: Forty-five lung tumors treated with RG-SBRT were enrolled. End-expiratory computed tomography (CT) (CTplan) and four-dimensional-CT (4D-CT) scans were obtained for planning. End-expiratory CT (CTfr) scanning was performed before each fraction. The FMs were divided into two groups based on the median tumor-FM distance in the CTplan (Dp). For the intra-fractional variation, the correlations between the corresponding tumor and FM intra-fractional motions, defined as the centroid coordinates of those in each 0-90% phase, with the 50% phase of 4D-CT as the origin, were calculated in the left-right, anterior-posterior, and superior-inferior directions. Furthermore, the maximum difference in the tumor-FM distance in each phase of 4D-CT scan, based on those in the 50% phase of 4D-CT scan (Dmax), was obtained. Inter-fractional variation was defined as the maximum distance between the tumors in CTplan and CTfr, when the CT scans were fused based on each FM or vertebra.

Results: The median Dp was 26.1 mm. While FM intra-fractional motions were significantly and strongly correlated with the tumor intra-fractional motions in only anterior-posterior and superior-inferior directions for the Dp > 26 mm group, they were significantly and strongly correlated in all directions for the Dp ≤ 26 mm group. In all directions, Dmax values of the Dp ≤ 26 mm group were lower than those of the Dp > 26 mm group. The inter-fractional variations based on the Dp ≤ 26 mm were smaller than those on the Dp > 26 mm and on the vertebra in all directions.

Conclusions: Regarding intra- and inter-fractional variation, FMs for Dp ≤ 26 mm can increase the accuracy for RG-SBRT.

Keywords: fiducial marker; lung tumor; stereotactic body radiation therapy.

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Conflict of interest statement

The authors have no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
Definition of the tumor and fiducial marker (FM) intra‐fractional motions (a), and Dmax for the evaluation of the intra‐fractional variation (b). Two items were considered in the evaluation of intra‐fractional variation using 4D‐CT scans: the correlation between tumor and FM intra‐fractional motions, and the difference between tumor and FM distance in each phase. (a) Tumor and FM intra‐fractional motions were defined as the centroid coordinates of the tumor and FM in each 0−90% phase, with the 50% phase of the 4D‐CT scanning used as the origin. (b) Dmax is defined as the maximum difference in the distance between the tumor and FM in each phase of 4D‐CT scanning based on the distance between the tumor and FM in the 50% phase of 4D‐CT scanning.
FIGURE 2
FIGURE 2
Definition of the inter‐fractional variation. Inter‐fractional variation was defined as the maximum distance between the centroid of the tumors captured on CT images at the end‐expiratory phase for treatment planning (CTplan) and before each fraction (CTfr) among CTfr‐based datasets when those CT scans were registered based on each fiducial marker (FM) or vertebra.
FIGURE 3
FIGURE 3
Scatter plot and Pearson's correlation coefficients between the corresponding tumor and fiducial marker (FM) motions defined as the centroid coordinates of the tumor and FM in each 0−90% phase with the 50% phase of the 4D‐CT scan as the origin. Those (a) in the left‐right, (b) the anterior‐posterior, and (c) the superior‐inferior directions for the Dp ≤ 26 mm group. (d) Left‐right, (e) anterior‐posterior, and (f) superior‐inferior directions in the Dp > 26 mm group.
FIGURE 4
FIGURE 4
Maximum differences of the distance between tumor and fiducial marker (FM) (Dmaxs) in the Dp ≤ 26 mm and in the Dp > 26 mm groups (a) in the left‐right, (b) the anterior‐posterior, and (c) the superior‐inferior directions. Dmax was defined as the maximum difference in the distance between the tumor and the FM in each phase of 4D‐CT scanning, based on the distance between the tumor and the FM in the 50% phase of 4D‐CT scans.
FIGURE 5
FIGURE 5
Differences of the inter‐fractional variations based on the Dp ≤ 26 mm group, on the Dp > 26 mm group, and on the vertebra (a) in the left‐right, (b) the anterior‐posterior, and (c) the superior‐inferior directions. Inter‐fractional variation was defined as the maximum distance between the centroid of the tumors in CT scans at end‐expiration for treatment planning (CTplan) and in CT scans at end‐expiration before each fraction (CTfr) among CTfr‐based datasets when the CT scans were fused based on each fiducial marker (FM) or vertebra.
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