Evaluation of motion compensation methods for non-invasive cardiac radioablation of ventricular tachycardia.

Abstract

PURPOSE\nNoninvasive cardiac radioablation is increasingly used for treatment of refractory ventricular tachycardia. Attempts to limit normal tissue exposure are important, including managing motion of the target. An interplay between cardiac and respiratory motion exists for cardiac radioablation, which has not been studied in depth. The objectives of this study were to estimate target motion during abdominal compression free breathing (ACFB) and respiratory gated (RG) deliveries, and to investigate the quality of either implanted cardioverter defibrillator (ICD) lead tip or the diaphragm as a gating surrogate.\n\n\nMETHODS\nEleven patients underwent CT simulation with an ACFB 4D-CT (r4DCT) and an exhale breath-hold cardiac 4D-CT (c4DCT). The target, ICD lead tip and diaphragm trajectories were measured for each patient on the r4DCT and c4DCT using rigid registration of each 4D phase to the reference (0%) phase. Motion ranges for ACFB and exhale (40%-60%) RG delivery were estimated from the target trajectories. Surrogate quality was estimated as the correlation with the target motion magnitudes.\n\n\nRESULTS\nMean (range) target motion across patients from r4DCT was Left/Right (LR) 3.9 (1.7-6.9), Anterior/Posterior (AP) 4.1 (2.2-5.4), Superior/Inferior (SI) 4.7 (2.2-7.9) mm. Mean (range) target motion from c4DCT was LR 3.4 (1.0-4.8), AP 4.3 (2.6-6.5), SI 4.1 (1.4-8.0) mm. For an ACFB treatment required mean (range) margins would be LR 4.5 (3.1-6.9), AP 4.8 (3-6.5), SI 5.5 (2.3-8.0) mm. For RG, mean (range) ITV motion would be LR 3.6 (1.1-4.8) mm, AP 4.3 (2.6-6.5) mm, and SI 4.2 (2.2-8.0) mm. The motion correlations between the surrogates and target showed a high level of inter-patient variability.\n\n\nCONCLUSIONS\nIn ACFB patients, a simulated exhale-gated approach did not lead to large projected improvements in margin reduction. Furthermore, the variable correlation between readily available gating surrogates could mitigate any potential advantage to gating, and should be evaluated on a patient specific basis.