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

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 ( ± $ \pm $ STD) across patients of (3.2 ± $\pm $ 1.7) mm under FB and (2.2 ± $ \pm $ 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.