Accuracy of routine treatment planning 4-dimensional and deep-inspiration breath-hold computed tomography delineation of the left anterior descending artery in radiation therapy.
OBJECTIVE
To assess the feasibility of radiation therapy treatment planning 4-dimensional computed tomography (4DCT) and deep-inspiration breath-hold (DIBH) CT to accurately contour the left anterior descending artery (LAD), a primary indicator of radiation-induced cardiac toxicity for patients undergoing radiation therapy.


METHODS
Ten subjects were prospectively imaged with a cardiac-gated MRI protocol to determine cardiac motion effects, including the displacement of a region of interest comprising the LAD. A series of planar views were obtained and resampled to create a 3-dimensional (3D) volume. A 3D optical flow deformable image registration algorithm determined tissue displacement during the cardiac cycle. The measured motion was then used as a spatial boundary to characterize motion blurring of the radiologist-delineated LAD structure for a cohort of 10 consecutive patients enrolled prospectively on a breast study including 4DCT and DIBH scans. Coronary motion-induced blurring artifacts were quantified by applying an unsharp filter to accentuate the LAD structure despite the presence of motion blurring. The 4DCT maximum inhalation and exhalation respiratory phases were coregistered to determine the LAD displacement during tidal respiration, as visualized in 4DCT.


RESULTS
The average 90th percentile heart motion for the region of interest was 0.7 ± 0.1 mm (left-right [LR]), 1.3 ± 0.6 mm (superior-inferior [SI]), and 0.6 ± 0.2 mm (anterior-posterior [AP]) in the cardiac-gated MRI cohort. The average relative increase in the number of voxels comprising the LAD contour was 69.4% ± 4.5% for the DIBH. The LAD volume overestimation had the dosimetric impact of decreasing the reported mean LAD dose by 23% ± 9% on average in the DIBH. During tidal respiration the average relative LAD contour increase was 69.3% ± 5.9% and 67.9% ± 4.6% for inhalation and exhalation respiratory phases, respectively. The average 90th percentile LAD motion was 4.8 ± 1.1 mm (LR), 0.9 ± 0.4 mm (SI), and 1.9 ± 0.6 mm (AP) for the 4DCT cohort, in the absence of cardiac gating.


CONCLUSIONS
An anisotropic margin of 2.7 mm (LR), 4.1 mm (SI), and 2.4 mm (AP) was quantitatively determined to account for motion blurring and patient setup error while placing minimum constraint on the plan optimization.
Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA. Electronic address: benjamin.white@uphs.upenn.edu.
Benjamin M
BM
White
L'Unità Operativa di Protonterapia, Azienda Provinciale per i Servizi Sanitari, Trento, Italy.
Sabina
S
Vennarini
Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA.
Lilie
L
Lin
Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA.
Gary
G
Freedman
Department of Radiation Oncology, University of California, Los Angeles, California.
Anand
A
Santhanam
Department of Radiation Oncology, University of California, Los Angeles, California.
Daniel A
DA
Low
Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA.
Stefan
S
Both
D000465:Algorithms; D016477:Artifacts; D001943:Breast Neoplasms / Q000473:pathology; D062485:Breath Holding; D055424:Cardiac-Gated Imaging Techniques; D003331:Coronary Vessels / Q000000981:diagnostic imaging* / Q000528:radiation effects*; D045853:Exhalation; D005240:Feasibility Studies; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006321:Heart / Q000528:radiation effects; D006801:Humans; D001239:Inhalation; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009068:Movement; D009200:Myocardial Contraction; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors