Program Information
Reproducibility of Breath-Hold Amplitude for Gated SBRT Plan Delivery
N Manohar*, J Rosenfield , E Elder , A Dhabaan , Emory University, Atlanta, GA
Presentations
WE-RAM2-GePD-T-5 (Wednesday, August 2, 2017) 10:00 AM - 10:30 AM Room: Therapy ePoster Lounge
Purpose: To assess reproducibility of breath-hold amplitude in abdominal, thoracic, and pelvic stereotactic body radiation therapy (SBRT) patients through evaluation of pre-treatment and treatment breathing waveforms.
Methods: The breathing waveforms captured by the Varian RPM system during 10 gated patient SBRT treatments with inspiration and expiration breath-holds were retrospectively analyzed. The treatment process involved gated capture of orthogonal images, making any necessary shifts, verification of patient anatomy matching by a physician, followed by the gated treatment. For each patient, the breathing patterns during the pre-treatment imaging and during treatment were evaluated. Specifically, the average amplitude of the breath-hold signal during treatment was compared to the amplitude during imaging for each fraction. A linear regression was used to compare the observed amplitudes, over the entire treatment course, to the ideal correlation (i.e., no difference between pre-treatment and treating breath-hold amplitude). Also, the absolute difference was quantified for each patient.
Results: The pre-treatment and treatment breath-hold amplitudes were well-correlated with a correlation coefficient (R2) of 0.9683. The average breath-hold amplitude during imaging and treatment were 0.715 and 0.785 cm, respectively, resulting in an average deviation of 0.7 mm. The minimum and maximum deviations were 0.07 mm and 3.75 mm, respectively. The majority of patients had deviations under 2 mm in magnitude
Conclusion: Even with minimal coaching, breath-hold amplitude appears to be reproducible over the timeline of a typical SBRT treatment course. On average, the dosimetric impact due to the observed sub-centimeter deviation of 0.7 mm is expected to be minimal. However, it would be beneficial to define an action level for the deviation so that any excursions may be subject to further review.
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