The role of abdominal compression in the reduction of respiratory motion for cardiac radioablation

Abstract Background Research on cardiac radioablation (CR) has highlighted the importance of accounting for respiratory‐induced motion during treatment, promoting investigation into methods to reduce its impact. Purpose To investigate the efficacy of abdominal compression (AC) to reduce respiratory‐induced motion for CR patients by quantifying their respiratory‐induced motion under AC and free breathing (FB) conditions. Methods and materials Nine patients were imaged with 5 Hz bi‐planar fluoroscopy on the Vero4DRT linear accelerator for 15–20 seconds under both AC and FB conditions in preparation for CR. As the soft tissue target is not visible on bi‐planar X‐ray images, the implantable cardioverter defibrillator (ICD) lead tip was used as a motion surrogate. The position of the ICD lead tip was tracked and triangulated in each bi‐planar image frame, with the respiratory component of motion extracted using a lowpass filter. Properties of respiratory‐induced motion were quantified including the average (across patient breaths) peak‐to‐peak motion extent, the mean total 3D magnitude of displacement, and the standard deviation of motion for each patient. Results The average (95% CI) extent of RV lead respiratory‐induced motion was [3.0 (1.1, 5.0), 2.8 (1.6, 4.1), 7.0 (4.2, 9.7)] mm under FB and [2.1 (1.4, 2.8), 2.7 (1.7, 3.8), 4.7 (3.5, 5.9)] mm under AC in the [right–left, anterior–posterior, inferior–superior] directions. Eight out of nine patients had a reduction in the mean respiratory‐induced total 3D displacement under AC, with an average ( STD) across patients of (3.2 1.7) mm under FB and (2.2 0.8) mm under AC. Averaged across patients, the standard deviation (95% CI) of respiratory‐induced motion was [1.3 (0.5, 2.0), 1.2 (0.7, 1.6), 3.1 (1.7, 4.5)] mm under FB and [0.9 (0.6, 1.3), 1.2 (0.6, 1.8), 2.0 (1.3, 2.7)] mm under AC. Conclusions For eight out of nine CR patients investigated, the respiratory‐induced RV lead motion was reduced when using AC compared to FB conditions.