Abstract
Atrial fibrillation (AFib) is the most common cardiac arrhythmia that affects millions of patients world-wide. AFib is usually treated with minimally invasive, time consuming catheter ablation techniques. While recently noninvasive radiosurgery to the pulmonary vein antrum (PVA) in the left atrium has been proposed for AFib treatment, precise target location during treatment is challenging due to complex respiratory and cardiac motion. A MRI linear accelerator (MRI-Linac) could solve the problems of motion tracking and compensation using real-time image guidance. In this study, the authors quantified target motion ranges on cardiac magnetic resonance imaging (MRI) and analyzed the dosimetric benefits of margin reduction assuming real-time motion compensation was applied. For the imaging study, six human subjects underwent real-time cardiac MRI under free breathing. The target motion was analyzed retrospectively using a template matching algorithm. The planning study was conducted on a CT of an AFib patient with a centrally located esophagus undergoing catheter ablation, representing an ideal case for cardiac radiosurgery. The target definition was similar to the ablation lesions at the PVA created during catheter treatment. Safety margins of 0 mm (perfect tracking) to 8 mm (untracked respiratory motion) were added to the target, defining the planning target volume (PTV). For each margin, a 30 Gy single fraction IMRT plan was generated. Additionally, the influence of 1 and 3 T magnetic fields on the treatment beam delivery was simulated using Monte Carlo calculations to determine the dosimetric impact of MRI guidance for two different Linac positions. Real-time cardiac MRI showed mean respiratory target motion of 10.2 mm (superior-inferior), 2.4 mm (anterior-posterior), and 2 mm (left-right). The planning study showed that increasing safety margins to encompass untracked respiratory motion leads to overlapping structures even in the ideal scenario, compromising either normal tissue dose constraints or PTV coverage. The magnetic field caused a slight increase in the PTV dose with the in-line MRI-Linac configuration. The authors' results indicate that real-time tracking and motion compensation are mandatory for cardiac radiosurgery and MRI-guidance is feasible, opening the possibility of treating cardiac arrhythmia patients completely noninvasively.
Highlights
Atrial fibrillation (AFib) is the most common type of cardiac arrhythmia and is considered a growing epidemic, with 45 estimates suggesting that up to 7M Americans[1] and more than 6M Europeans[2] are affected
The motion of the left atrium (LA) was measured using template matching on cine magnetic resonance imaging (MRI) scans of the beating heart during free breathing
Differential motion of the distal pulmonary veins and the complex contraction pattern of the LA were not investigated in this study
Summary
Atrial fibrillation (AFib) is the most common type of cardiac arrhythmia and is considered a growing epidemic, with 45 estimates suggesting that up to 7M Americans[1] and more than 6M Europeans[2] are affected. AFib has been shown to increase the risk of ischemic strokes and heart failure by up to five times and is the underlying cause for 20% of all strokes.[1] AFib is caused by aberrant electrical impulses originating from the atria of the heart, mostly from the pulmonary veins entering the left atrium (LA). These signals disturb the natural sinus rhythm of the heart, leading to inefficient atrial contractions at high frequencies (more 50 than 600 beats per minute) which favor blood clot formation and irregular heartbeats. Geriatric patients and those with cardiac comorbidities have low success 55 rates and are mostly ineligible for this invasive and highly stressful procedure.[3]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
