Program Information
Image-Guided Radiation Therapy Using Synthetic CTs in Brain Cancer
R.G. Price1,2*, J. Kim2 , W. Zheng2 , I.J. Chetty2 , C. Glide-Hurst1,2 , (1) Wayne State School of Medicine, Detroit, MI, (2) Henry Ford Health System, Detroit, MI
Presentations
SU-G-JeP2-8 (Sunday, July 31, 2016) 4:30 PM - 5:00 PM Room: ePoster Theater
Purpose: Synthetic-CTs(synCTs) are essential for MR-only treatment planning. However, the performance of synCT for IGRT must be carefully assessed. This work evaluated the accuracy of synCT and synCT-generated DRRs and determined their performance for IGRT in brain cancer radiation therapy.
Methods: MR-SIM and CT-SIM images were acquired of a novel anthropomorphic phantom and a cohort of 12 patients. SynCTs were generated by combining an ultra-short echo time (UTE) sequence with other MRI datasets using voxel-based weighted summation. For the phantom, DRRs from synCT and CT were compared via bounding box and landmark analysis. Planar (MV/KV) and volumetric (CBCT) IGRT performance were evaluated across several platforms. In patients, retrospective analysis was conducted to register CBCTs (n=34) to synCTs and CTs using automated rigid registration in the treatment planning system using whole brain and local registration techniques. A semi-automatic registration program was developed and validated to rigidly register planar MV/KV images (n=37) to synCT and CT DRRs. Registration reproducibility was assessed and margin differences were characterized using the van Herk formalism.
Results: Bounding box and landmark analysis of phantom synCT DRRs were within 1mm of CT DRRs. Absolute 2D/2D registration shift differences ranged from 0.0-0.7mm for phantom DRRs on all treatment platforms and 0.0-0.4mm for volumetric registrations. For patient planar registrations, mean shift differences were 0.4±0.5mm (range: -0.6-1.6mm), 0.0±0.5mm, (range: -0.9-1.2mm), and 0.1±0.3mm (range: -0.7-0.6mm) for the superior-inferior(S-I), left-right(L-R), and anterior-posterior(A-P) axes, respectively. Mean shift differences in volumetric registrations were 0.6±0.4mm (range: -0.2-1.6mm), 0.2±0.4mm (range: -0.3-1.2mm), and 0.2±0.3mm (range: -0.2-1.2mm) for S-I, L-R, and A-P axes, respectively. CT-SIM and synCT derived margins were within 0.3mm.
Conclusion: DRRs generated via synCT agreed well with CT-SIM. Planar and volumetric registrations to synCT-derived targets were comparable to CT. This validation is the next step toward clinical implementation of MR-only planning for the brain.
Funding Support, Disclosures, and Conflict of Interest: The submitting institution has research agreements with Philips Healthcare. Research sponsored by a Henry Ford Health System Internal Mentored Grant.
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