MR only Radiation Treatment Planning

Magnetic resonance imaging (MRI) has emerged as a key component in modern radiotherapy. The superior soft tissue contrast compared to computed tomography (CT) allows for increased accuracy in the definition of both target and organs at risk using commonplace sequences.

Functional imaging techniques, primarily diffusion-weighted imaging and dynamic contrast enhanced imaging, are currently studied as a means of identifying areas within a tumor that require a higher dose in dose-painting trials.

Several current studies also aim to evaluate the possibilities of early treatment response assessment using MRI, which could enable treatment adaptation. At present, the main rationale of integrating MRI into the radiotherapy workflow is the gain in accuracy in target volume definitions. For several major patient groups, MR imaging is preferable from a medical point of view, i.e. for tumor definition. CT or CT equivalent information is still, however, required for the technical aspects of treatment planning such as:

• accurate dose calculations, which depend on knowledge of the attenuation properties of the tissue measured in a CT exam

• generation of reference images which are used for patient positioning based on in-room X-ray imaging.

Therefore, it is common practice to acquire both CT and MR data and align these image series in the same coordinate system, or frame of reference, through image registration. The MR data is used to define the target volume and the CT data to plan the treatment and serve as a reference for patient positioning. This workflow is, however, not optimal for several reasons. Besides the increase in cost and workload when using multiple imaging modalities, there is also an introduction of additional geometrical uncertainty due to the image registration.

We are evaluating three current synthetic CT techniques

1- Manual bulk density assignment

2- Atlas methods

3- Direct conversion

Aim 1. Correct for any MRI geometrical distortions (System and Patient specific), be sure to guarantee the spatial accuracy of tumor and normal tissue within a millimeter.

Aim 2. Generated synthetic computed tomography (Synthetic CT) images comparable with CT for dose calculation.

Aim 3. Assessing the Dosimetry Accuracy of Magnetic Resonance-Generated Synthetic CT Images for Focal Brain Radiation Therapy (VMAT, IMRT and SRS)

Assessing Magnetic Resonance-Generated Synthetic-CT Images for Brain MR guided Radiation Treatment Planning (MRgRTP): A Feasibility Study

Purpose: This feasibility study investigated the dosimetric accuracy of synthetic-CT images derived from MR images for stand-alone intracranial focal brain treatment planning. Synthetic-CT images allow more accurate volume delineation resulting in better tumor control probability and normal tissue sparing. Initial results were compared to conventional CT-based and homogeneous patient density treatment plans.

Methods: MR and CT images were acquired for a brain patient. Synthetic-CT images were generated from MR images using a syngo.via Frontier prototype software (Siemens Healthcare). The physician defined target and normal tissues on a separate T1 MR image set, then both the synthetic-CT and MR images with structures were rigidly aligned to the CT. A VMAT SRT plan (25Gy in 5 fractions) was designed on the CT set (with and without heterogeneity correction), and the plan was transferred exactly to the synthetic-CT images. PTV coverage and hot spot along with normal tissue doses were analyzed, as well as gradient metrics. Finally, 2-dimensional analyses of dose distributions were performed using 1%/1mm gamma criteria.

Results: PTV coverage (V₁₀₀) for the CT, synthetic-CT, and homogeneous calculations was 95.7%, 97.1%, and 99.1%, respectively. Normal tissue doses were comparable. R_50%(V_50%/V_100%) values were 4.59, 4.45, and 4.32. Max doses were 29.8Gy, 30.3Gy, and 30.8Gy. Gamma analysis showed passing agreement of 97.6% and 96.8% for comparisons of the synthetic-CT and homogeneous calculation relative to the CT dose distribution, respectively.

Conclusions: Synthetic-CT compared favorably to the homogeneous calculation when analyzed relative to the CT image set. These initial feasibility study results indicate that accurate dose calculation from a MR generated synthetic-CT may be advantageous with the benefit of MR accurate structure delineation and dose calculation accuracy exceeding that achieved with a homogeneous density calculation. In addition, this study indicated that ignoring heterogeneity corrections in brain region could give the clinician false target coverage.

Publications

Ali Fatemi, Bart Moris, Chunli Claus Yang, Edward Florez, Sirinvasan Vijayakumar, Mahhava Madhava R. Kanakamedala, Somayeh Taghizadeh,“Multiparametric quantitative MRI as a metric for radiation treatment planning”, Theranostics of Can Res. 1(1). TCR.000503. 2017
Bart Morris, Claus Yang, Madhava Kanakamedala, Sirinvasan Vijayakumar, Ali Fatemi, WE-RAM3-GePD-J(B)-03, ”Assessing Magnetic Resonance-Generated Synthetic-CT Images for Brain MR Guided Radiation Treatment Planning (MRgRTP): A Feasibility Study”, Med Phys, 2016 Jun;43(6):505
H Yu, Ali Fatemi, A Sahgal, SU‐E‐J‐224: “ Using UTE and T1 Weighted Spin Echo Pulse Sequences for MR‐Only Treatment Planning; Phantom Study”, Med Phys, 2015, Jun, 42(6), 3317
S Mashouf, Ali Fatemi, W Song, SU‐E‐J‐233: “ Effect of Brachytherapy Seed Artifacts in T2 and Proton Density Maps in MR Images”, Med Phys, 2015, Jun, 42(6), 3319
A Soliman, A Elzibak, Ali Fatemi, H Safigholi, D Han, E Leung, A Ravi, W Song, SU‐E‐T‐208: “ Comparison of MR Image Quality of Various Brachytherapy Applicators for Cervical Cancer “Med Phys, 2015, Jun, 42(6), 33806.
A Soliman, A Elzibak, Ali Fatemi, H Safigholi, D Han, A Ravi, G Morton, W Song, TU‐AB‐201‐11: “ A Novel Theoretical Framework for MRI‐Only Image Guided LDR Prostate and Breast Brachytherapy Implant Dosimetry”, Med Phys, 2015, Jun, 42(6), 3596
Ali Fatemi, J Borg, SU‐D‐213CD‐05: “ Identifying Prostate Brachytherapy Seeds at MRI: A Study in Phantom”, Med Phys, 2012, Jun (39), 3618
Ali Fatemi, Edward Florez, Somayeh Taghizadeh, Hamid Khosravi, Claus Chunli Yang, Srinivasan Vijayakumar, Roberto Rey-Dios, Bart Morris, William N. Duggar, Madhava R. Kanakamedala, “Geometric analysis of target volume definition using corrected MRI images and analysis of their use for stereotactic radiosurgery treatment planning”. (Submitted for general summer AAPM 2018 meeting)
Ali Fatemi, Somayeh Taghizadeh, Madhava R. Kanakamedala, Claus Chunli Yang, Roberto Rey-Dios, Bart Morris, William N. Duggar, Himanshu Bhat and Fernando Vega, Srinivasan Vijayakumar, “Clinical significance of inhomogeneities in stereotactic radiosurgery treatment planning using synthetic CT images”, (Submitted for general summer AAPM 2018 meeting)
Ali Fatemi, Edward Florez, Somayeh Taghizadeh, Hamid Khosravi, Claus Chunli Yang, Srinivasan Vijayakumar, Roberto Rey-Dios, Bart Morris, William N. Duggar, Madhava R. Kanakamedala, “ Accuracy of co-registration of Synthetic CT planning images with CBCT for stereotactic radiosurgery (SRS) on Gamma knife icon machine”. (Manuscript in preparation for submission to the journal of Medical Physicis)
Ali Fatemi, Edward Florez, Somayeh Taghizadeh, Hamid Khosravi, Claus Chunli Yang, Srinivasan Vijayakumar, Roberto Rey-Dios, Bart Morris, William N. Duggar, Madhava R. Kanakamedala .” Implication of using corrected MRI for intracranial stereotactic radiosurgery (SRS) compare with MRI co-registered with CT”, ”. (Manuscript in preparation for submission to the journal of Medical Physicis)
Ali Fatemi, Edward Florez, Somayeh Taghizadeh, Hamid Khosravi, Claus Chunli Yang, Srinivasan Vijayakumar, Roberto Rey-Dios, Bart Morris, William N. Duggar, Madhava R. Kanakamedala .“To develop a clinically feasible workflow of 4D MRIbased treatment planning for liver SBRT”, (Manuscript in preparation for submission to the journal of clinical oncology)
Ali Fatemi, Edward Florez, Bart, Claus Chunli Yang, Bart Morris, William N. Duggar, Srinivasan Vijayakumar, “Software solution to use on board CBCT for adaptive head and neck radiotherapy”, (Manuscript in preparation for submission to the journal of clinical oncology)
Ali Fatemi , Edward Florez, Madhava R. Kanakamedala, Sirinvasan Vijayakumar Clinical application of susceptibility weighted imaging (SWI) in stereotactic radiosurgery (SRS) treatment planning and post radiation evaluation, (Manuscript in preparation for submission to the journal of Radiology)

Google Sites

Report abuse