PV QA 3 - Poster Viewing Q&A 3
TU_19_3304 - Cardiac Gating Improves Dosimetry for Intracardiac Proton Radiation Therapy Targets
Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3
Cardiac Gating Improves Dosimetry for Intracardiac Proton Radiation Therapy Targets
H. Lee1, V. Muralidhar2, J. Pursley3, H. M. Lu4, T. F. DeLaney4, J. A. Adams1, K. W. Jee1, and Y. L. E. Chen4; 1Massachusetts General Hospital, Boston, MA, 2Harvard Radiation Oncology Program, Boston, MA, 3Harvard Medical School, Boston, MA, 4Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA
Purpose/Objective(s): Intracardiac radiation targets have gained increased interest due to the possibility of irradiating primary cardiac tumors (e.g. sarcomas), hemodynamically compromising metastases, and foci of cardiac arrhythmias. Irradiation of the heart is complicated by cardiac motion throughout the cardiac cycle. We sought to determine whether gating proton radiation to the cardiac cycle via surface electrocardiogram (EKG) might improve cardiac dosimetry, especially with regard to non-target cardiac structures receiving radiation. Materials/Methods: We used a sample patient with an EKG-gated four-dimensional computed tomography (4DCT) scan to model irradiation of cardiac targets in the left ventricle free wall, interventricular septum, right atrium, and right ventricle. We contoured the target as well as critical cardiac structures, including the whole heart, left ventricle, right ventricle, right atrium, and coronary arteries. For each possible target location, we first modeled target and normal cardiac dosimetric parameters for a variety of proton beam angles and selected the optimal beam arrangement for each target. Second, using the optimal proton beam angles, we modeled the effect of gating the proton beam delivery to end-diastole or end-systole on cardiac dosimetric parameters. Results: For a target in the left ventricle free wall, EKG gating to end-diastole significantly improved mean radiation dose to the whole heart (20.5 Gy vs 13.0 Gy, 36.6% reduction) and left ventricle (45.0 Gy vs 29.5 Gy, 34.4% reduction). Similarly, for a target in the interventricular septum, EKG gating to end-diastole improved the mean heart dose (20.5 Gy vs 15.5 Gy, 24.4% reduction) and left ventricle dose (18 Gy vs 11.5 Gy, 36.1% reduction). For targets in the right atrial free wall and within the right ventricle, cardiac gating was associated with a 10% or less improvement in radiation dose to nearby critical structures (i.e. right coronary artery, whole heart, and left ventricle) regardless of the gating phase. Conclusion: EKG gating improves proton dosimetry for intracardiac targets for tumors in certain cardiac locations (e.g. left ventricle and interventricular septum), but not others, possibly due to differences in the degree of motion throughout the cardiac cycle. EKG gating may be a promising approach to reduce dose to normal cardiac structures when irradiating intracardiac targets, including intracardiac tumors and arrhythmogenic foci, even when highly conformal proton radiotherapy is used.
Author Disclosure: H. Lee: None. V. Muralidhar: None. J. Pursley: None. H. Lu: Employee; Massachusetts General Hospital. T.F. DeLaney: None. Y.E. Chen: Employee; Beth Israel Deaconess Medical Center.