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Retrospectively Evaluating CBCT Target Localization with MIP-Based Alignment and Comparing with AIP-Based Alignment

L Wang1*, (1) Fox Chase Cancer Center, Philadelphia, PA

Presentations

PO-GePV-M-148 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

ePoster Forums

Purpose: To determine whether maximum or average intensity projection (MIP or AIP, respectively) reconstructed from 4-dimensional computed tomography (4DCT) is preferred for alignment to cone beam CT (CBCT) images in lung stereotactic body radiation therapy (SBRT).

Methods: 4DCT images were acquired for all the lung SBRT patients in our institution. Both MIP and AIP image sets were reconstructed from the 4DCT. MIP and AIP image sets were fused and internal target volumes (ITVs) were delineated from the MIP. AIP image set was used for treatment planning. For imaging guidance prior to the treatment delivery, primary planning images (AIP) and all the structures were sent to Varian OBI system. For each fraction, a CBCT was obtained and aligned with MIP-based ITV. For this study, both CBCT-based GTV and AIP-based GTV were retrospectively contoured for 15 patients. The alignments between the centers of the GTV in CBCT and AIP were compared with that of the alignments between CBCT and MIP.

Results: The difference between two types of alignments is very small (0.0074, 0.0645, 0.128 mm in x, y, and z direction). However, in general, the volume of the CBCT-based GTV is larger than that of the AIP-based GTV. The average volume difference is 2.47 cc. Thus, the CBCT-based GTV generally appeared outside of the AIP-based GTV, but well within the MIP-ITV. The MIP-based ITV has the largest volume (average 18.598 cc compared to 9.671 cc in CBCT and 7.203 cc in AIP) and can well encompass the CBCT-based GTV.

Conclusion: AIP and MIP registration do not seem to make any difference in the localization because the location of the target center is the same on both MIP and AIP. However, MIP is preferred for CBCT alignment due to its nature in encompassing all the phase of motions.

Keywords

Image Guidance, Target Localization

Taxonomy

Not Applicable / None Entered.

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