(Tuesday, 7/16/2019) 10:00 AM - 10:30 AM
Room: Exhibit Hall | Forum 9
Purpose: To clinically investigate the limited-projection CBCT (LP-CBCT) technology for daily positioning of patients receiving breath-hold lung SBRT radiation treatment and to investigate the feasibility of reconstructing fast 4D-CBCT from 1 min 3D-CBCT scan.
Methods: Eleven patients who underwent breath-hold lung SBRT radiation treatment were scanned daily with on-board full-projection CBCT (FP-CBCT) using half-fan scan. A subset of the FP-CBCT projections and the prior planning CT were used to estimate the LP-CBCT images using the weighted free-form deformation method. The limited projections are clusteringly sampled within fifteen sub-angles in 360° in order to simulate the fast 1 min scan for 4D-CBCT. The estimated LP-CBCTs were rigidly registered to the planning CT to determine the clinical shifts needed for patient setup corrections, which were compared with shifts determined by the FP-CBCT for evaluation. Both manual and automatic registrations were performed in order to compare the systematic registration errors. Fifty FP-CBCT volumes were obtained from the eleven patients for this pilot clinical study.
Results: For the FP-CBCT images, the mean (±standard deviation) shifts between FP-CBCT and planning CT from manual registration in left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions are 1.1±1.2 mm, 2.1±1.9 mm, 5.2±3.6 mm, respectively. The mean deviation difference between shifts determined by FP-CBCT and LP-CBCT images are 0.3±0.5 mm, 0.5±0.8 mm, 0.4±0.3 mm, in LR, AP, and SI directions, respectively. The mean vector length of FP-CBCT shift for all fractions is 6.1±3.6 mm, and the mean vector length difference between FP-CBCT and LP-CBCT for all fractions studied is 1.0±0.9 mm.
Conclusion: This pilot clinical study shows that LP-CBCT localization offers comparable accuracy to FP-CBCT localization for daily tumor positioning while reducing the projection number to 1/10. The cluster projection sampling in this study also shows the feasibility of reconstructing fast 4D-CBCT from 1 min 3D-CBCT scan.
Funding Support, Disclosures, and Conflict of Interest: This work is partially supported by the NIH under Grant No. R01-CA184173.
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