(Saturday, 4/4/2020) [Mountain Time (GMT-6)]
Purpose: The purpose of this work is to develop a method to verify, in real-time, the reproducibility of the liver dome for each breath-hold for liver SBRT patients during radiation therapy treatment delivery.
Methods: Two patients treated with SBRT to the superior aspect of the liver using the Active Breathing Coordinator (ABC) breath-hold device were included in this work. kV planar images acquired every 60° of the gantry rotation during VMAT delivery were used to manually trigger the beam on/off based on the location of the diaphragm. Physician drawn contours of the liver for three repeated CT simulation scans were overlaid onto the kV images and used to guide the triggering. Post-treatment, the triggered images were exported from the treatment console and the distance from a manually drawn contour of the liver dome to the liver contours was calculated and compared to a clinically acceptable positional tolerance of 5-mm.
Results: For both patients, there were multiple instances where the beam was manually triggered off due to diaphragm position compared to the liver contours demonstrating the clinical value of this technique. For patient 1, the maximum and mean distance from the liver dome in kV images to the liver contours was greater than the 5-mm PTV margin for 31% and 10% of all triggered images. For patient 2, the maximum and mean distance from the liver dome to the liver contours was greater than 5-mm for 46% and 14% of all triggered images.
Conclusion: The verification technique for breath-hold reproducibility presented in this work was able to identify breath-hold variations that were outside of planned margins according to the internal anatomy of the liver for SBRT patients during treatment. Future work will increase the size of the data while evaluating the dosimetric impact of the breath-hold variability in these patients.
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