Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_19_3305 - Analysis of Cardiac Motion without Respiratory Motion for Cardiac Stereotactic Body Radiation Therapy

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Analysis of Cardiac Motion without Respiratory Motion for Cardiac Stereotactic Body Radiation Therapy
Z. Ouyang1, P. Schoenhagen2,3, O. Wazni3, P. Tchou3, W. I. Saliba3, J. H. Suh1, and P. Xia1; 1Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, 2Department of Diagnostic Radiology, Cleveland Clinic, Cleveland, OH, 3Department of Cardiovascular Medicine, Cleveland Clinic, Cleveland, OH

Purpose/Objective(s): Using stereotactic body radiation therapy (SBRT) instead of catheter radiofrequency ablation to treat ventricular tachycardia has achieved promising initial results. However, cardiac motion during SBRT and treatment margin requirements are not fully understood. In this work, we studied the heart motion using gated cardiac computed tomography (CT) images to provide guidance on treatment planning margins during cardiac SBRT with breath-hold.

Materials/Methods: Ten patients who received gated cardiac CT scans were included. Images were acquired while patients were asked to perform a voluntary breath-hold using a dual source CT scanner. A retrospectively gated acquisition of the heart was performed following intravenous contrast administration. Images were reconstructed with 1 mm slice thickness in multiple phases (10%–90%) of the cardiac cycle. For each patient, the left ventricle (LV), ascending aorta (AAo), ostia of the right coronary artery (O-RCA), and left coronary artery (O-LCA) were contoured at each phase. Displacements of the contour centroids at each phase from the average positions in the superior-inferior (SI), medial-lateral (ML), and anterior-posterior (AP) were assessed individually.

Results: For the ten patients, as shown in Table 1, the average displacements were: for LV, 0.51±0.53 mm in the SI direction, 0.53±0.43 mm in the ML direction, 1.20±0.83 mm in the AP direction; for AAo, 0.48±0.38 mm in the SI direction, 0.96±0.78 mm in the ML direction, 1.30±0.84 mm in the AP direction; for O-RCA, 0.97±0.83 mm in the SI direction, 1.64±1.17 mm in the ML direction, 1.62±1.00 mm in the AP direction; for O-LCA, 1.06±0.82 mm in the SI direction, 1.24±0.87 mm in the ML direction, 1.21±0.85 mm in the AP direction. The maximum displacements were within 5 mm, and the average displacements were within 2 mm. Among the four structures, O-RCA was observed to have the largest maximum displacements in all directions.

Conclusion: Based on this study, cardiac motion is variable but is within 5 mm. Depending on the location (central or peripheral) of the target, the planning margin for a specific lesion should be adjusted accordingly. Future study includes full assessment on heart motion and the dosimetric differences due to the target location. Table 1. Absolute displacements of the LV, AAo, O-RCA, O-LCA in a cardiac cycle for ten patients.
Displacement (mm)
Contour Direction Average Standard Deviation Min Max
LV SI 0.51 0.53 0.00 3.24
ML 0.53 0.43 0.00 2.32
AP 1.20 0.83 0.04 3.44
AAo SI 0.48 0.38 0.01 1.95
ML 0.96 0.78 0.02 3.43
AP 1.30 0.84 0.09 3.14
O-RCA SI 0.97 0.83 0.00 3.72
ML 1.64 1.17 0.11 4.96
AP 1.52 1.00 0.02 3.92
O-LCA SI 1.06 0.82 0.02 3.32
ML 1.24 0.87 0.02 3.66
AP 1.21 0.85 0.01 3.16

Author Disclosure: Z. Ouyang: None. P. Schoenhagen: None. W.I. Saliba: None. J.H. Suh: Consultant; ACMUI. Board member; Korean American Society for Therapeutic Radiation. P. Xia: Employee; Cleveland Clinic. Research Grant; Philips Healthcare.

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