Exhibit Hall | Forum 5
Purpose: To introduce a new gated treatment technique for breath-hold liver stereotactic body radiation therapy (SBRT) based on liver dome positions.
Methods: Twenty-five liver SBRT patients were included. All patients were treated with breath-hold using Active Breathing Coordinator and volumetric modulated arc therapy. KV planar images (triggered images) were acquired at the beginning of each breath-hold during treatment. The liver dome positions in the triggered images were visually compared with the upper and lower liver boundaries, which were created by expanding and contracting liver contour 0.5 cm in the superior-inferior direction, respectively. The beam was held and the breath-hold was discarded if the liver dome position was out of the defined boundary.To analyze breath-hold reproducibility during treatment, the liver dome was delineated on each triggered image. The mean distance between the delineated liver dome to the planning liver contour was defined as liver dome position error.
Results: Triggered images of 713 breath-holds from 92 treatment fractions were analyzed. For each patient, an average of 1.5 breath holds (range 0-7) were discarded due to liver dome position outside of the boundary, accounting for 5% (0-18%) of all breath holds. Comparing the liver dome position errors with and without gating, for each patient, the mean and maximum position errors of all breath-holds were reduced from average 0.31 cm (range 0.13-0.61 cm) to 0.27 cm (0.12-0.52 cm), and from 0.86 cm (0.30-1.80 cm) to 0.67 cm (0.30-0.90 cm), respectively. The percentage of breath-holds with position error >0.5 cm was reduced from 15% (0-42%) without gating to 11% (0-35%) with gating. Gating eliminated breath-holds with position error >1cm, which happened in 3% (0-17%) of all breath-holds.
Conclusion: Using liver dome positions to evaluate breath-hold reproducibility and gate beam delivery is feasible. Gated treatments improve treatment accuracy for breath-hold liver SBRT.