Clinical Evaluation of Digital Tomosynthesis for Target Localization in Breath-Hold Liver Treatment

Article Outline

• Purpose/Objective(s)
• Material/Methods
• Results
• Conclusions
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Purpose/Objective(s) 

On-board DTS images is preferable for breath-hold (BH) treatment as it can be acquired within 1 single BH (<10 sec.), while BH-CBCT requires multiple breath-hold sessions and takes 3–5 min. This study is to examine target verification accuracy of on-board BH digital tomosynthesis (BH-DTS), compared with BH-CBCT for liver treatment.

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Material/Methods 

11 patients were retrospectively studied. All image sets were acquired under BH. Reference DTS images (BH-RDTS) were generated from the planning CT and BH-DTS images were reconstructed using 40 degrees of the projection images acquired during BH-CBCT. Target alignment was performed manually by matching the planning CT to the CBCT, coronal RDTS to on-board coronal DTS, and sagittal RDTS to on-board sagittal DTS, for a total of 22 imaging sessions. 6 of 11 patients had clips (14 fractions). Target verification was performed based on (1) bony anatomy, (2) soft tissue target and/or liver, and (3) clips when present. The alignment accuracy is analyzed as the difference between DTS and CBCT based alignments (Fig.).

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Results 

The alignment accuracy analysis of the above three methods is detailed in Table 1. For bony anatomy based alignment, the accuracy is within 0.2 cm for both coronal and sagittal DTS. The standard deviation is slightly worse for soft tissue based alignment compared with bony alignment. Among three methods, alignment using clips had least deviation.

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Conclusions 

Either bony anatomy based or soft tissue based target alignment is achievable with BH-DTS. Clips, if present, are suitable surrogates for soft tissue matching. BH-DTS is more efficient for daily 3D on-board image guidance and localization when breath-hold treatment is delivered. Partially supported by a grant from Varian Medical Systems.

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Table 1. Alignment Accuracy of DTS compared with CBCT (unit in cm)

	Coronal-DTS			Sagittal-DTS
	Lat	Vert	Long	Lat	Vert	Long
Bony anatomy based
Mean	0.1	−0.1	0.0	0.1	0.0	−0.1
Standard Deviation	0.5	0.3	0.4	0.6	0.2	0.2
Soft tissue based
Mean	0.1	0.1	0.0	0.2	0.1	0.0
Standard Deviation	0.6	0.4	0.4	0.7	0.3	0.5
Clips based
Mean	0.1	0.1	−0.1	0.2	0.1	−0.1
Standard Deviation	0.3	0.5	0.3	0.4	0.3	0.3