Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations

1. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Six Week Project – MEDBIO 3970Z April 04, 2012 Trevor Thang Department of Medical Biophysics, Western University Supervisor: Dr. Eugene Wong, Physics and Astronomy Rob Bartha, Charles McKenzie, Aaron Ward, Glenn Bauman

2. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Acknowledgements • Dr. CesareRomagnoli • Dr. Blaine Chronik • Trevor Szekere • Eli Gibson • Funding supported in part by • OCAIRO, ORF • CIHR-STP

3. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations MOTIVATION • CANCER – Endogenous Disease • Radiotherapy – High Energy • X-Rays, Gamma Rays, etc. • Result: • Multiple irradiations over long periods of time • New Variables

4. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations MOTIVATION • Adaptive Radiotherapy • Most common: Adapt patient to Treatment Plan • Geometric Information from linear accelerator on-board CT imaging • Ultimate Goal: Adapt radiotherapy based on treatment response

5. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations MOTIVATION • To access the Tumor’s Response to Therapy: • Employ functional imaging • Compare baseline and mid-treatment images • Adapt treatment based on changes in the images • But …

6. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Motivation Are the Changes in the Images: Biological? or Inconsistent Imaging?

7. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations BACKGROUND Objectives • Develop Patient-Specific Quality Assurance Metrics • For MR Spectroscopy Since MRS data is labour intensive to generate and analyze … Can Volumetric Distortions in DW-EP Images be used as surrogate for MRS quality assessments?

8. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Methods MR SPECTROSCOPY • MRS analyzed using fitMANdeveloped by Bartha’s group • For 11 patients, • Load Patient Raw Data • Exponential Filter in frequency domain to reduce noise • Remove the Residual Water Signal • Lipid Signal Rephased

9. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations BACKGROUND Magnetic Resonance Spectroscopy • Different peaks correspond to protons in different chemical environment • Inhomogeneous Magnetic Fields produce Large FWHM

10. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations BACKGROUND Volumetric Distortion in DW-EPI • Spatial Information Encoded with the Use of Magnetic Gradients • Gx – Frequency Encoding, Gy – Phase Encoding, Gz – Slice Encoding 3 • T2w Images Unsusceptible • 180° Refocusing Pulse • Gold Standard • Inhomogeneous Field • ↓ • Improper Spatial Encoding • ↓ • Deformation 3 MR Pulse Sequences: What Every Radiologist Wants to Know but Is Afraid to Ask. Bitar

11. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations METHOD • Patient Data • From London’s CIHR funded multi-parametric MR of prostate cancer patients imaged prior to prostatectomy • Identified 11 patients with single voxel MRS data • Employed deformed volume in Diffusion weighted Echo Planar Imaging (DW-EPI) as a gauge of B0 uniformity • Correlate deformed Volume with FWHM MRS data.

12. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations METHODS PROSTATE SEGMENTATION on Pinnacle • AX T2w – FSE • Unsusceptible due to 180° Refocusing Pulse • DW-EPI • Susceptibledue to lack of 180° Refocusing Pulse Patient B Patient A

13. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Methods Volumetric Percent Difference examples 2.5% 21% 6.8% 4.1%

14. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations RESULTS

15. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Results Residual Water as a Surrogate for Main Magnetic Field Uniformity N = 11 FWHM (Hz) = 1.2 * %Diff +4.4 R² = 0.82

16. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Results Lipid as a Surrogate for Main Magnetic Field Uniformity N = 11 R² = 0.63 FWHM (Hz) = 1.9 * %Diff +20

17. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Results Lipid as a Surrogate for Main Magnetic Field Uniformity N = 10 R² = 0.87 FWHM (Hz) = 1.5 * %Diff +24

18. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Results Volumetric Deformation Threshold • Acceptable FWHM Lipid MRS ≤ 35 Hz at 3T • Issues: • Volumetric contours have uncertainties. • Other Metrics to Measure Distortion • Surface Area-to-Volume Ratio • Volumetric Overlap

19. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Next Steps • ROC Analysis with more patient data • Validate Volume Threshold Values • Determine Other Direct Methods detecting InhomogenousB0 • Phase Difference Method 4 • Bandwidth-Difference (∆BW)5 Downfall: These all come with the cost of increased patient scanning time. 4Magnetic Resonance Imaging Quality Control Manual (American College of Radiology), Weinreb, 1991 5 Routine Testing of Magnetic Field Homogeneity on clinical MRI Systems. Hua-Hsuan Chen, 2006

20. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Summary • Employed deformation in DW-EPI as surrogates for B0 homogeneity, correlating this to the FWHM of MRS • Potential Indicator of Quality of MRS data: • DW-EPI Volumetric Percent Change ≤ 7% • If this threshold is exceeded, the data should not be used. • In the present 11 patient cohort, 4 were deemed unacceptable • Analyze the citrate and choline peaks for the remaining 7 patients. • Will Validate correlation with double the patient data.