(Tuesday, 7/31/2018) 10:00 AM - 10:30 AM
Room: Exhibit Hall | Forum 5
Purpose: To clinically investigate the limited-angle CBCT (LA-CBCT) technology for daily positioning of patients receiving breath hold lung radiation treatment and to compare its positioning accuracy to conventional full-angle CBCT (FA-CBCT).
Methods: Six patients who underwent breath hold lung radiation treatment were scanned daily with on-board FA-CBCT. A subset of the FA-CBCT projections (30 out of ~900) in a limited angle (90°) and the prior planning CT were used to estimate the LA-CBCT images. Using the limited angle projections from anterior-posterior, lateral, or oblique angles in the CBCT scanning, three sets of on-board LA-CBCT images were estimated separately (LA-CBCT(AP), LA-CBCT(LAT), and LA-CBCT(OBL)) using the weighted free-form deformation method. The LA-CBCTs were registered to the CT to determine the clinical shifts needed for patient setup correction, which were compared with shifts determined by the FA-CBCT for evaluation. Seventy-eight LA-CBCTs and twenty-six FA-CBCTs were obtained from the six patients in twenty-six fractions for this pilot clinical study.
Results: For the FA-CBCT images, the mean (±standard deviation) shifts between FA-CBCT and planning CT in left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions are 3.0±3.7mm, 2.6±2.1mm, 5.8±3.5mm, respectively. The mean±standard deviation difference between shifts determined by CBCT and LA-CBCT(AP) images are 0.4±0.4mm, 0.7±0.8mm, 0.8±1.3mm, in LR, AP, and SI directions, respectively. And those for LA-CBCT(LAT) and LA-CBCT(OBL) images are 1.4±1.4 mm, 1.1±1.2mm, 1.7±1.7mm, and 0.9±0.9mm, 1.0±0.8mm, 0.9±0.8mm, respectively. The mean vector length of FA-CBCT shift for all fractions is 7.9±4.1 mm, and the mean vector length set up errors between FA-CBCT and LA-CBCT(AP), LA-CBCT(LAT), LA-CBCT(OBL) for all fractions are 1.4±1.3mm, 2.7±2.1mm, 1.9±1.1mm, respectively.
Conclusion: The pilot clinical study shows that for patient receiving breath hold lung radiation treatment, LA-CBCT localization offers comparable accuracy to FA-CBCT localization for daily tumor positioning while reducing mechanical constraints and imaging dose.
Funding Support, Disclosures, and Conflict of Interest: This work is supported by the National Institutes of Health under Grant No R01-CA184173 and a research grant from Varian Medical Systems.
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