Department of Radiation Oncology University of Michigan

Department of Radiation Oncology University of Michigan

Volumetric Arc treatment planning in the brain using synthetic CT images

James M. Balter, Shu-Hui Hsu, Karen Vineberg, Mary Feng, Christina Tsien, Yue Cao

Supported by NIH R01 EB016079 and Siemens Medical Systems

Methods

• 5 patients with gliomas underwent MRI and CT simulations

• MRI volumes were processed using a fuzzy clustering technique to generate synthetic CT (“MRCT”) volumes, which were aligned to CT volumes

• VMAT plans were generated using the same priorities and structures on CT (6 times) and MRCT

• MRCT-derived fluences were also used for dose recalculation using CT-derived density grid

Example plans from CT and MRCT

Example of VMAT plans optimized on CT (left panels) and MRCT (right panels)-derived density grids. Dose volume histograms are shown for the brainstem PRV, right eye, left eye, right optic nerve PRV, chiasm PRV, left optic nerve PRV and PTV.

Results

• No statistically significant dose differences between plans optimized on MRCT and on CT

• Largest dose difference variations in distal optic nerve max dose (s 1.9 Gy)

• Larger differences seen in max doses when comparing calculations using MRCT-derived fluences on MRCT versus CT density grids

Ongoing study – improved MRCT acquisition and processing

Example study patient

Patient scanned with new technique

MRCT CT MRCT CT MRCT CT

Results (optional slide)

Dose metricMRCT-CT average

(Gy) s

MRCT calc on MRCT - CT

average (Gy) sPrimary PTV D99% -0.03 0.12 -0.38 1.33Primary PTV D95% -0.03 0.08 -0.57 1.46

Proximal Optic nerve max dose -0.81 1.03 -1.85 1.63

Distal Optic nerve max dose -2.02 1.92 -1.73 3.02Brainstem max dose -0.19 0.89 -1.77 2.32

Brainstem D10% 0.48 0.40 -1.23 1.71

chiasm max dose -0.59 0.71 -1.76 2.69Left eye max dose -0.18 0.22 -0.45 0.98Right eye max dose -0.82 0.80 -1.64 3.06