1. 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

2. 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

3. 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.

4. Results No statistically significant dose differences between plans optimized on MRCT and on CT Largest dose difference variations in distal optic nerve max dose (  1.9 Gy) Larger differences seen in max doses when comparing calculations using MRCT-derived fluences on MRCT versus CT density grids

5. Ongoing study – improved MRCT acquisition and processing Example study patient Patient scanned with new technique MRCT CT MRCT CT MRCT CT

7. Results (optional slide) Dose metric MRCT-CT average (Gy)  MRCT calc on MRCT - CT average (Gy)  Primary PTV D99%-0.030.12-0.381.33 Primary PTV D95%-0.030.08-0.571.46 Proximal Optic nerve max dose-0.811.03-1.851.63 Distal Optic nerve max dose-2.021.92-1.733.02 Brainstem max dose-0.190.89-1.772.32 Brainstem D10%0.480.40-1.231.71 chiasm max dose-0.590.71-1.762.69 Left eye max dose-0.180.22-0.450.98 Right eye max dose-0.820.80-1.643.06