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TU‐EF‐304‐04: A Heart Motion Model for Proton Scanned Beam Chest Radiotherapy
Author(s) -
White B,
Kiely J Blanco,
Vennarini S,
Lin L,
Freedman G,
Santhanam A,
Low D,
Both S
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4925659
Subject(s) - cardiac cycle , image registration , nuclear medicine , medicine , biomedical engineering , mathematics , cardiology , artificial intelligence , computer science , image (mathematics)
Purpose: To model fast‐moving heart surface motion as a function of cardiac‐phase in order to compensate for the lack of cardiac‐gating in evaluating accurate dose to coronary structures. Methods: Ten subjects were prospectively imaged with a breath‐hold, cardiac‐gated MRI protocol to determine heart surface motion. Radial and planar views of the heart were resampled into a 3‐dimensional volume representing one heartbeat. A multi‐resolution optical flow deformable image registration algorithm determined tissue displacement during the cardiac‐cycle. The surface of the heart was modeled as a thin membrane comprised of voxels perpendicular to a pencil beam scanning (PBS) beam. The membrane's out‐of‐plane spatial displacement was modeled as a harmonic function with Lame's equations. Model accuracy was assessed with the root mean squared error (RMSE). The model was applied to a cohort of six chest wall irradiation patients with PBS plans generated on phase‐sorted 4DCT. Respiratory motion was separated from the cardiac motion with a previously published technique. Volumetric dose painting was simulated and dose accumulated to validate plan robustness (target coverage variation accepted within 2%). Maximum and mean heart surface dose assessed the dosimetric impact of heart and coronary artery motion. Results: Average and maximum heart surface displacements were 2.54±0.35mm and 3.6mm from the end‐diastole phase to the end‐systole cardiac‐phase respectively. An average RMSE of 0.11±0.04 showed the model to be accurate. Observed errors were greatest between the circumflex artery and mitral valve level of the heart anatomy. Heart surface displacements correspond to a 3.6±1.0% and 5.1±2.3% dosimetric impact on the maximum and mean heart surface DVH indicators respectively. Conclusion: Although heart surface motion parallel to beam's direction was substantial, its maximum dosimetric impact was 5.1±2.3%. Since PBS delivers low doses to coronary structures relative to photon radiotherapy, it is unknown whether this variation would be clinically significant for late effects.