Breath-Hold Cone Beam CT (CBCT): Improved Image Quality With “Stop-and-Go” Breath Hold–Only Acquisition Versus Repetitive Breath Hold During Continuous Rotation

Breath-hold CBCT imaging for SABR (Stereotactic Ablative Body Radiation therapy) has been performed at our department with repeated breathhold with approximately 60% of the dataset being acquired in breathhold phases during one continuous CBCT rotation (2 minutes). This has established a complete computer-controlled deep inspiration breathhold (DIBH)-workflow from treatment planning to delivery. This method is clinically used and has been proven to be sufficient for high-precision image matching. It is now technically possible to stop the gantry rotation during free-breathing phases and acquire CBCT images during breathhold phases only (“stop-and-go” approach). Here we compare image quality of CBCT in DIBH-only “stop-and-go” acquisition vs repeat DIBH CBCT during continuous rotation. A patient with a lung metastasis of a soft tissue tumor has been treated with SABR (60Gy, 12 times 5Gy fractions). Before each daily fraction, CBCT images were acquired. CBCT in DIBH-only “stop-and-go” acquisition and repeat DIBH CBCT during continuous rotation were compared quantitatively using grey value gradients that were calculated by taking the square root of the sum of the squares of the image gradients in x and y directions. Around the tumor and the diaphragm a region of interest (ROI) was defined. In this ROI the mean and standard deviation of the gradient image were calculated over the central 10 slices defining the sharpness of the image. Acquisition time of a breath-hold only stop-and-go CBCT was 4 min vs 2 min for repeat-DIBH CBCT. Blurring was reduced in the stop-and-go breath-hold-only CBCT vs repeat-DIBH CBCT acquired during continuous gantry rotation. Upon objective grey-value analysis, sharpness for the breath-hold-only images was increased by (13.8 ± 2.5)% for the tumor ROI and (19.9 ± 1.9)% for the diaphragm ROI compared to the repetitive breath-hold images reconstructed from 60% breathhold phases. Breath-hold only CBCT with “stop-and-go” acquisition further improved image quality and reduced blurring over acquisition in repetitive DIBH during continuous rotation at the cost of a longer time to acquire a full image dataset. Imaging time can be reduced further by combining kV and MV imaging for a full CBCT acquisition in a single breath-hold.