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Evaluating Geometric and Dosimetric Accuracy of Synthetic CT Images for MRI-Only Stereotactic Radiosurgery

S Bagherimofidi*, C Yang , W Duggar , M Kanakamedala , A Fatemi , Department of Radiation Oncology, University of Mississippi Med. Center, Jackson, MS


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: We sought to determine and validate the clinical significance and accuracy of synthetic CT images for inhomogeneity correction in MRI-only stereotactic radiosurgery plans for treatment of brain tumors

Methods: In this retrospective study, we analyzed data from twenty patients who received frameless SRS treatment. Synthetic CT images were generated from MR images using syngo.via RT Image Suite (Siemens Healthineers) using a fuzzy c-means method. Experienced physicians rigidly registered the CT and MRI image datasets and defined the target volume on MR images, and a physicist created SRS treatment plans using MR images and the TMR10 algorithm. SRS doses were prescribed in the range of 13–20 Gy to 50% to 75% isodose lines according to lesion sizes. The volumes were transferred to synthetic CT and CT images; this information was used for planning on both synthetic CT and CT datasets using the convolution algorithm, with the same dose prescription as on primary MRI images. Dose maps were calculated on the synthetic CT and on the original CT data using the same plan parameters.

Results: Dose distributions appeared similar for both CT and synthetic CT plans, and both were more conformal than TMR10-derived plans. Overall, 1.84% decrease was observed for maximum point dose inside the targets for synthetic CT, and a 1.67% decrease for CT plans compared with TMR10. The average D100 and D95 for synthetic CT showed a 0.13% increase and 0.2% decrease compared with a 0.68% increase and 0.75 % increase in CT-based compared to MRI plans. Overall, synthetic CT plans provided better coverage and a lower maximum dose.

Conclusion: The results of this study show similarity between CT and synthetic CT-based SRS plans. In addition, synthetic CT offered a noticeable improvement in target dose coverage and a more gradual dose fall off.


MRI, Gamma Knife


IM/TH- MRI in Radiation Therapy: MRI for treatment planning

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