Trevor Thang Department of Medical Biophysics, Western University QUALITY ASSURANCE OF MRI FOR ADAPTIVE RADIOTHERAPY: PRELIMINARY INVESTIGATIONS Six Week Project – MEDBIO 3970Z April 04, 2012 Supervisor: Dr. Eugene Wong, Physics and Astronomy Rob Bartha, Charles McKenzie, Aaron Ward, Glenn Bauman

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

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

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

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? BACKGROUND Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations

MR SPECTROSCOPY METHODS MRS analyzed using fitMAN developed by Bartha’s group For 11 patients, 1.Load Patient Raw Data 2.Exponential Filter in frequency domain to reduce noise 3.Remove the Residual Water Signal 4.Lipid Signal Rephased Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations

MAGNETIC RESONANCE SPECTROSCOPY Different peaks correspond to protons in different chemical environment Inhomogeneous Magnetic Fields produce Large FWHM BACKGROUND Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations

Spatial Information Encoded with the Use of Magnetic Gradients G x – Frequency Encoding, G y – Phase Encoding, G z – Slice Encoding 3 T2w Images Unsusceptible 180° Refocusing Pulse Gold Standard VOLUMETRIC DISTORTION IN DW-EPI BACKGROUND Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Inhomogeneous Field ↓ Improper Spatial Encoding ↓ Deformation 3 MR Pulse Sequences: What Every Radiologist Wants to Know but Is Afraid to Ask. Bitar

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 B 0 uniformity Correlate deformed Volume with FWHM MRS data. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations

PROSTATE SEGMENTATION ON PINNACLE AX T2w – FSE Unsusceptible due to 180° Refocusing Pulse DW-EPI Susceptible due to lack of 180° Refocusing Pulse METHODS Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations Patient A Patient B

VOLUMETRIC PERCENT DIFFERENCE EXAMPLES METHODS 21%6.8%4.1%2.5% Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations

RESULTS Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations

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

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

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

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 RESULTS Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations

NEXT STEPS Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations 4 Magnetic Resonance Imaging Quality Control Manual (American College of Radiology), Weinreb, Routine Testing of Magnetic Field Homogeneity on clinical MRI Systems. Hua-Hsuan Chen, 2006

SUMMARY Employed deformation in DW-EPI as surrogates for B 0 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. Quality Assurance of MRI for Adaptive Radiotherapy: Preliminary Investigations