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UBC Theses and Dissertations

Cardiac synchronized volumetric modulated arc therapy Poon, Justin


Cardiac arrhythmias are abnormal heart rhythms that can adversely affect patients. The current treatment options include antiarrhythmic drug therapy and catheter ablation, both of which are associated with issues regarding efficacy and potential complications for complex arrhythmias. Cardiac radiosurgery, external beam therapy targeted at abnormal myocardial substrate, has the potential to be a non-invasive and efficient treatment option for arrhythmias. Intrafraction heart motion, however, must be accounted for to ensure accurate dose delivery to the target region. Our technique aims to minimize the dose delivered to normal tissues by synchronizing beam delivery with a cardiac signal, irradiating only during the quiescent intervals of the cardiac cycle (when heart motion is minimal) and adjusting the beam delivery speed in response to a changing heart rate. Although real-time treatment plan adaptation is not possible with the current linear accelerator systems, we demonstrated the feasibility of our technique by synchronizing beam delivery with sample ECG data. A conventional VMAT plan was split into 3 interleaved phases – each phase consists of alternating beam-on and beam-off arc segments, and the combination of all phases recreates the original plan. Each phase was synchronized with a sample cardiac signal, using movement of the treatment couch to adjust the durations of individual arc segments. The cardiac synchronized phases were created as XML beam files and were delivered in developer mode of the Varian TrueBeam system. Analysis of the trajectory logs showed that all beam-on segments were delivered during the quiescent intervals as planned. Film dosimetry was used to verify the dose delivery accuracy of the cardiac synchronized beams. A custom table was built and positioned over the treatment couch, allowing for a phantom placed on the table surface to remain stationary during beam delivery. Film was inserted in the phantom and irradiated using the original treatment plan, then a separate film was inserted and irradiated using the cardiac synchronized phases. Analysis of the films in FilmQA Pro returned a gamma passing rate of 99.4% (2%/2mm tolerance), indicating excellent agreement between the dose distributions of the original and cardiac synchronized beam deliveries.

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