mri

Methods to Differentiate Radiation Induced Necrosis and Recurrent Disease in Gliomas

Lars Ewell University of Arizona Medical Center

Department of Radiation Oncology

MRI Research Group2/2/07

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Methods to Differentiate Radiation Induced Necrosis and Recurrent Disease in Gliomas

I. Introduction: The ProblemII. Radiation Damage: Brain vs. TumorIII. Similarities/DifferencesIV. MRS: Metabolite RatiosV. DWMRI: ADCVI. ABRC GrantVII. Conclusion

Radiation Induced Necrosis

• Radiation is one of the few proven currently known methods to increase survival and quality of life for glioma (brain tumor) patients.

• Radiation dose has been correlated with recurrence.

• Too much radiation can kill normal brain tissue.

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Radiation Dose

[dose] = Energy/Mass and the SI unit of dose = Gray = Gy = 1J/Kg.

• Lethal dose is ~4Gy given to the whole body in ~ seconds.

• Typical Rx dose for a glioma is 60Gy given in 30 Fx (2Gy/Fx) over 6 weeks.

• Diagnostic dose (CAT Scan) ~10cGy.

• Dose with the energy imparted by ionizing radiation to material of mass .

m

m

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Radiation Damage: Cell Survival

• The ratio has units of dose, and is used to determine tissue radiation reaction.

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100

10-1

10-2Su

rviv

ing

Frac

tion

Radiation Dose (Gy)4 8 12

2DDeS • The ‘linear – quadratic’

model of cell survival, w/ S the surviving fraction, D the dose and constants.

Radiation Damage: Early - Late

• The ratio has been correlated with response time for radiation damage to manifest.

• For brain and/or spinal cord, ~ 2Gy indicating a late radiation response (months to years).

• For tumor, ~ 10 Gy indicating an early radiation response (weeks to months).

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RIN/Recurrent Disease

• T1 weighted contrast enhanced MRI taken 16 months after completion of radiotherapy (left).

• Same MRI taken 2 months, 15 days later.

• Biopsy later revealed no evidence of recurrent tumor.

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Kumar et al., Radiology, 217, 2, November 2000.

RIN/Recurrent Disease: Comparison1. ‘Enhancing lesion’

on MRI. 2. Origin at or near

primary site. 3. Growth over time.

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1. Additional radiation can benefit recurrent disease.

2. Additional radiation detrimental to RIN.

Similarities:

Differences:

DWMRI to Distinguish RIN and Recurrent Disease

• Since RIN may have same characteristics as successfully treated tumor, one may think that using DWMRI could differentiate RIN from recurrent disease.

• However, initial studies show little value in using DWMRI to differentiate RIN and recurrent disease. Limited resolution of DWMRI one problem.

• Radial Fast Spin Echo (RFSE) promises better DWMRI resolution.

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Magnetic Resonance Spectroscopy

• MRS, also called Chemical Shift Imaging (CSI), gets signal from shift in resonance due to surrounding chemical environment.

• Using MRS, the ratio of brain metabolites such as Choline (Cho), Creatine (Cr) and N-Acetylaspartate (NAA) can be measured.

• These ratios have been shown to have power to discriminate RIN and recurrent disease.

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MRS Metabolites

• Cho is a neurotransmitter and is increased in tumors. Correlated with high cellular density.

• NAA is a metabolite found in neurons, and is decreased in tumors.

• Cr is a brain metabolite and is also decreased in tumors.

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Metabolite Ratios for Different Tissue

00.5

11.5

22.5

33.5

44.5

5

1 2 3R

atio

Cho/Cr

Cho/NAA

NAA/Cr

RadiationInduced Necrosis

WhiteMatter

RecurrentTumor

• 2D CSI scans given to seven patients.

• 16cm FOV, 16x16 and slice thickness of 10-20mm.

• 1 average, scan time of 4 min., 20sec.

• Absence of tumor confirmed by biopsy in two patients.

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*

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Weybright et al., Neuroradiology (2004) 46: 541–549

*

MRS Metabolite Ratios

Magnetic Resonance Spectroscopy

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ChoCr

NAA

MRS

• ‘Quick and Dirty’ 2D multi-voxel scans taken 1/25/07 – pre and post Gd.

• 3:18 with 2 NEX.• 3x3cm voxels, 1cm

thick.• Disease visible in

voxel #2.

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MRS: Normal vs. Disease

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Voxel # 7 - Normal Voxel # 2 - Disease

MRS: Pre vs. Post Gd

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Pre Gd Post Gd

Magnetic Resonance Spectroscopy

• Although MRS has been shown to have discriminating power, there are two problems associated with it: 1) Low resolution. 2) Long scan time.

• Imaging protocol will join MRS with RFSE DWMRI to create synergistic combination.

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Arizona Biomedical Research Commission

• Grant Awarded: Diffusion Weighted MRI and Magnetic Resonance Spectroscopy to Differentiate Radiation Necrosis and Recurrent Disease in Gilomas (PI LAE).

• Enroll 60 patients diagnosed with a glioma (metastatic or primary) and follow longitudinally.

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Imaging Protocol• Patients eligible to enroll if they have a

reasonable risk of suffering from RIN.• Published data indicate that patients

receiving a dose of 60Gy in 30 Fx have between a 5 and 24% chance of developing RIN.

• Hypo-fractionation and Stereotactic Radio-Surgery (SRS) are also forms of radiation Tx.

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Imaging Protocol: Enrollment Criteria

• Biological Equivalent Dose (BED) used to determine enrollment criteria for hypo-fractionation and SRS.

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• BED = nd(1 + ) with n the number of fractions, d the dose, and

the linear quadratic constants.

/d

• 5 x 6Gy required for hypo - fractionation, 21Gy for SRS.

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Imaging Protocol: Enrollment Criteria

Radiation Type Number of Fractions

Minimum Radiation (Gy)

SRS 1 21

Hypo-fraction 5 30

Normal Fraction 30 60

Re-treatment varies varies

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Imaging Protocol: Imaging SequenceTime from End of

Radiotherapy (days)Scans Performed Comments

-5 CT, MRI, DWMRI, MRS

Baseline scans. Used to plan radiotherapy. CT

and MRI registered using Brainscan.

30 MRI, DWMRI, MRS First scan for comparison.

90 MRI, DWMRI, MRS Second scan for comparison. Potential

radiation necrosis.Check ADCW for change.

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Imaging Protocol

• VOI centered at center of resection cavity.

• 2D Multi-voxel CSI with 1cm slice thickness. 7x7cm.

• Three slices, ~8:30 for each slice, one centered on lesion and one superior and inferior.

• MRS will take majority of time.

Center of Resection Cavity

Regions to be Longitudinally Monitored

1cm2cm

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Imaging Protocol

• Current ‘Gold Standard’ for confirming glioma vs. RIN is pathologic examination of biopsy.

• We expect that ~50% of enrolled patients will undergo biopsy at some point.

• Vector Vision should locate biopsy location to within ~2mm.

• Biopsy MRI registered with protocol MRI using Brainscan software.

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Imaging Protocol

• Approved by SRC 11/14/06.• Third submission to IRB will take place

early next week. • Expect approval shortly thereafter –

2/13/07• Patient enrollment thereafter.

Conclusion

• DWMRI and MRS are non-invasive forms of medical imaging that show promise for differentiation between RIN and recurrent disease in glioma patients.

• It will take work to realize the full potential of these complimentary imaging forms.

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Acknowledgement

• Chris Watchman, Russ Hamilton• Dino Stea, Marco Marsella• Thomas Chong• Scott Squire• Jamie Holt

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