MRI Assessment of Cardiac Radioablation Lesion at the Cavotricuspid Isthmus in Mini Pigs.

Abstract

PURPOSE/OBJECTIVE(S)\nStereotactic body radiotherapy (SBRT) is an emerging non-invasive treatment in the management of cardiac arrhythmias. The purpose of this research is to evaluate the MR imaging in the detection of radioablation lesion at the cavotricuspid isthmus (CTI) in mini pigs.\n\n\nMATERIALS/METHODS\nFour mini pigs underwent magnetic resonance (MR) evaluation of heart function and invasive electrophysiology assessment using electroanatomical mapping (EAM) before and 3 months after SBRT with single-fraction doses of 25Gy at the CTI. SBRT simulation, planning, and treatments were performed with the use of standard techniques. MR examination, including diffusion-weighted MRI, dynamic Gd-enhanced MRI, MR spectroscopy, and T2-weighted MRI were performed before and 3 months after SBRT, followed by histopathologic examination. One radiation oncologist and one radiologist evaluated the detectability and image quality for the irradiated site. MRI findings of the CTI radioablation lesion was compared to electrophysiology and histopathology findings.\n\n\nRESULTS\nA total dose of 25 Gy was delivered to the CTI (median volume of 25 cc) in a single procedure according to the radiation therapy oncology group. The mean radiation dose to the heart was 7 Gy. The maximal doses (< 0.05 cc) to the left and right coronary arteries were 14 Gy and 13 Gy, respectively. EAM visualized the irradiated site and confirmed clockwise conduction block across the CTI. Gd-enhanced T1-weighted imaging could only detect the irradiated site. There were no statistical differences in the image quality of the all MR images.\n\n\nCONCLUSION\nThese data demonstrated the feasibility of SBRT for creating conduction block across the CTI in mini pigs. Gd-enhanced T1-weighted imaging was essential in assessing the radioablation lesion.