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Phantom investigation of 3D motion-dependent volume aliasing during CT simulation for radiation therapy planning.

Tanyi JA, Fuss M, Varchena V, Lancaster JL, Salter BJ - Radiat Oncol (2007)

Bottom Line: Slow-scan percentage overestimations were larger, and better approximated the time-averaged motion envelope, as opposed to fast-scans.Motion induced centroid misrepresentation was greater in the S-I direction for fast-scan techniques, and transaxial direction for the slow-scan technique.Overestimation is fairly uniform for slice widths < 5 mm, beyond which there is gross overestimation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, University of Arizona Health Science Center, Tucson, AZ 85724, USA. jtanyi@email.arizona.edu

ABSTRACT

Purpose: To quantify volumetric and positional aliasing during non-gated fast- and slow-scan acquisition CT in the presence of 3D target motion.

Methods: Single-slice fast, single-slice slow, and multi-slice fast scan helical CTs were acquired of dynamic spherical targets (1 and 3.15 cm in diameter), embedded in an anthropomorphic phantom. 3D target motions typical of clinically observed tumor motion parameters were investigated. Motion excursions included +/- 5, +/- 10, and +/- 15 mm displacements in the S-I direction synchronized with constant displacements of +/- 5 and +/- 2 mm in the A-P and lateral directions, respectively. For each target, scan technique, and motion excursion, eight different initial motion-to-scan phase relationships were investigated.

Results: An anticipated general trend of target volume overestimation was observed. The mean percentage overestimation of the true physical target volume typically increased with target motion amplitude and decreasing target diameter. Slow-scan percentage overestimations were larger, and better approximated the time-averaged motion envelope, as opposed to fast-scans. Motion induced centroid misrepresentation was greater in the S-I direction for fast-scan techniques, and transaxial direction for the slow-scan technique. Overestimation is fairly uniform for slice widths < 5 mm, beyond which there is gross overestimation.

Conclusion: Non-gated CT imaging of targets describing clinically relevant, 3D motion results in aliased overestimation of the target volume and misrepresentation of centroid location, with little or no correlation between the physical target geometry and the CT-generated target geometry. Slow-scan techniques are a practical method for characterizing time-averaged target position. Fast-scan techniques provide a more reliable, albeit still distorted, target margin.

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Related in: MedlinePlus

Fast- and slow-scan distortion of the 10- and 31.5-mm diameter targets as a function of four (4) initial motion phases and three (3) motion amplitudes. The top row of images ("a" and "b") is associated with the 10 mm target, while the bottom row ("c" and "d") with the 31.5 mm target. The columns of structures labeled "STATIC" are surrogate representations of the respective 10- and 31.5-mm diameter targets. Image sets "a" and "c" are reconstructions from single-slice fast techniques, while "b" and "d" are from single-slice slow scan techniques. The motion amplitudes presented on the figures are for the S-I direction and are synchronized with constant ± 2 and ± 5 mm displacements in the R-L and A-P directions, respectively.
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Figure 4: Fast- and slow-scan distortion of the 10- and 31.5-mm diameter targets as a function of four (4) initial motion phases and three (3) motion amplitudes. The top row of images ("a" and "b") is associated with the 10 mm target, while the bottom row ("c" and "d") with the 31.5 mm target. The columns of structures labeled "STATIC" are surrogate representations of the respective 10- and 31.5-mm diameter targets. Image sets "a" and "c" are reconstructions from single-slice fast techniques, while "b" and "d" are from single-slice slow scan techniques. The motion amplitudes presented on the figures are for the S-I direction and are synchronized with constant ± 2 and ± 5 mm displacements in the R-L and A-P directions, respectively.

Mentions: For qualitative appreciation of motion-induced volumetric distortion during CT imaging, frontal views of the dGTVs for both the small and large targets are presented in Fig 4. It is apparent that there is little similarity between the dGTVs and the sGTV (the sGTV being a proxy representation of the true geometry of each corresponding target).


Phantom investigation of 3D motion-dependent volume aliasing during CT simulation for radiation therapy planning.

Tanyi JA, Fuss M, Varchena V, Lancaster JL, Salter BJ - Radiat Oncol (2007)

Fast- and slow-scan distortion of the 10- and 31.5-mm diameter targets as a function of four (4) initial motion phases and three (3) motion amplitudes. The top row of images ("a" and "b") is associated with the 10 mm target, while the bottom row ("c" and "d") with the 31.5 mm target. The columns of structures labeled "STATIC" are surrogate representations of the respective 10- and 31.5-mm diameter targets. Image sets "a" and "c" are reconstructions from single-slice fast techniques, while "b" and "d" are from single-slice slow scan techniques. The motion amplitudes presented on the figures are for the S-I direction and are synchronized with constant ± 2 and ± 5 mm displacements in the R-L and A-P directions, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1808462&req=5

Figure 4: Fast- and slow-scan distortion of the 10- and 31.5-mm diameter targets as a function of four (4) initial motion phases and three (3) motion amplitudes. The top row of images ("a" and "b") is associated with the 10 mm target, while the bottom row ("c" and "d") with the 31.5 mm target. The columns of structures labeled "STATIC" are surrogate representations of the respective 10- and 31.5-mm diameter targets. Image sets "a" and "c" are reconstructions from single-slice fast techniques, while "b" and "d" are from single-slice slow scan techniques. The motion amplitudes presented on the figures are for the S-I direction and are synchronized with constant ± 2 and ± 5 mm displacements in the R-L and A-P directions, respectively.
Mentions: For qualitative appreciation of motion-induced volumetric distortion during CT imaging, frontal views of the dGTVs for both the small and large targets are presented in Fig 4. It is apparent that there is little similarity between the dGTVs and the sGTV (the sGTV being a proxy representation of the true geometry of each corresponding target).

Bottom Line: Slow-scan percentage overestimations were larger, and better approximated the time-averaged motion envelope, as opposed to fast-scans.Motion induced centroid misrepresentation was greater in the S-I direction for fast-scan techniques, and transaxial direction for the slow-scan technique.Overestimation is fairly uniform for slice widths < 5 mm, beyond which there is gross overestimation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, University of Arizona Health Science Center, Tucson, AZ 85724, USA. jtanyi@email.arizona.edu

ABSTRACT

Purpose: To quantify volumetric and positional aliasing during non-gated fast- and slow-scan acquisition CT in the presence of 3D target motion.

Methods: Single-slice fast, single-slice slow, and multi-slice fast scan helical CTs were acquired of dynamic spherical targets (1 and 3.15 cm in diameter), embedded in an anthropomorphic phantom. 3D target motions typical of clinically observed tumor motion parameters were investigated. Motion excursions included +/- 5, +/- 10, and +/- 15 mm displacements in the S-I direction synchronized with constant displacements of +/- 5 and +/- 2 mm in the A-P and lateral directions, respectively. For each target, scan technique, and motion excursion, eight different initial motion-to-scan phase relationships were investigated.

Results: An anticipated general trend of target volume overestimation was observed. The mean percentage overestimation of the true physical target volume typically increased with target motion amplitude and decreasing target diameter. Slow-scan percentage overestimations were larger, and better approximated the time-averaged motion envelope, as opposed to fast-scans. Motion induced centroid misrepresentation was greater in the S-I direction for fast-scan techniques, and transaxial direction for the slow-scan technique. Overestimation is fairly uniform for slice widths < 5 mm, beyond which there is gross overestimation.

Conclusion: Non-gated CT imaging of targets describing clinically relevant, 3D motion results in aliased overestimation of the target volume and misrepresentation of centroid location, with little or no correlation between the physical target geometry and the CT-generated target geometry. Slow-scan techniques are a practical method for characterizing time-averaged target position. Fast-scan techniques provide a more reliable, albeit still distorted, target margin.

Show MeSH
Related in: MedlinePlus