Exhibit Hall | Forum 3
Purpose: Radioablation is a promising, non-invasive method to treat refractory cardiac arrhythmias. During treatment, the target moves as a result of cardiac and respiratory motion. We evaluated the dosimetric impact to target, cardiac substructures, and other organs due to the interplay of motion and treatment delivery.
Methods: Thirteen ventricular tachycardia patients treated with cardiac radioablation (single dose of 25 Gy) were retrospectively identified. The original plans were produced on either the 4DCT average or a free breathing CT using a 10MV FFF VMAT technique. The jaw, MLC positions and MUs from the delivery log files were associated with the individual phase CTs based on the log timestamp and patient breathing cycle. The planned VMAT arcs were split into 8 sets of sub-plans that were registered to the 8 phase image set. The total dose was summed on the planning CT from the calculated sub-plans using deformable image registration. The dosimetric parameters were evaluated against the original plans to assess the motion effect.
Results: All but one patient had decreased PTV coverage due to respiratory motion; however, the ITV and GTV coverage remained robust except in two patients. The D0.03cc to the stomach showed a median increase in the range of 1.5-6.1 Gy in six patients due to motion. Atriums, ventricles, coronary and left ascending-descending arteries generally showed slightly reduced dose among all the patients, except four patients who had an increase in the range of 0.52-1.61 Gy in the D0.03cc of several cardiac substructures.
Conclusion: The dosimetric effect due to respiratory motion was not significant in most patients, including dose to the cardiac substructures. A few patients could have received reduced target coverage or increased maximum dose to the stomach. The results can be used to correlate with potential cardiac and other critical organ radio-toxicities.