Implementation of MR-Based Synthetic CT for Stereotactic Radiosurgery Dose Calculation

Abstract

Most Gamma Knife stereotactic radiosurgery (GKRS) procedures have been performed using water-based dose calculation algorithms with magnetic resonance imaging (MRI) only. We present a dose calculation method that can take into account the inhomogeneity effect in routine GKRS treatment planning without CT imaging for every patient.Twenty-five patients who underwent GKRS at our institution with T1- and T2-weighted whole head MRI as well as brain CT images were selected for this study. Two set of synthetic computed tomographies (sCT) were generated from T1 and T2 MRI using cycle consistent generative adversial networks architecture (cGAN). Images from 20 patients were used to train the algorithm. The other 5 sets of data were used for testing and validation. The sCT images generated were evaluated in terms of the preservation of anatomical structures, the Hounsfield unit accuracy and the overall image quality. All sCT images from the 5 test patients were imported into GammaPlan version 11.1 for dosimetric analyses. We performed dose calculations for each test patient using the water-based TMR algorithm and the convolution algorithm with electron densities from the original CT, the T1-based sCT and the T2-based sCT.The main features of the original CT images (skull shape, bone & air inhomogeneity etc.) for the 5 test patients were successfully reproduced in the sCT images. sCT images from the T1-weighted MRI are in general closer to the original CT images compared to the T2-weighted MR images. For the same dose prescription and same shot arrangement, the maximum difference between the treatment shot times from the CT-based convolution calculation and the TMR calculation is 10.2%. The maximum differences between the treatment shot times from the CT-based convolution calculation and the convolution calculations from the sCTs from the T1 and T2 MR images are 2.3% and 3.8%, respectively.sCT images from brain MRI can be used for the inhomogeneity correction in GKRS dose calculation. T1-weighted MRI may work better than T2-weighted MRI for this purpose.F. Li: None. Y. Xu: None. O.D. Lemus: None. T.J. Wang: Research Grant; AbbVie, Merck, RTOG Foundation, Genentech. Honoraria; Elekta, Wolters Kluwer, Cancer Panels, Rutgers, University of Iowa. Consultant; Doximity, Elekta. Advisory Board; Novocure, AstraZeneca. Travel Expenses; AbbVie, Elekta, Novocure. Stock Options; Doximity. M.B. Sisti: None. C. Wuu: None.