Molecular Imaging Instrumentation for the Prostate

Comparison of Bremsstrahlung SPECT/CT and PET/CT for Y-90 QuantificationNeal ClinthornePaul KisonJill RothleyYuni Dewaraja

Department of RadiologyDivision of Nuclear MedicineThe University of MichiganAnn Arbor, MI USAnclintho@umich.edu

1Y-90 ImagingDesirable for verifying distribution of Y-90 microspheres used in SIRT for unresectable liver cancer

Can potentially be used for dosimetry

Possible with both SPECT and PET

Goal was to compare performance of PET and SPECT using existing commercial acquisition and reconstruction

22Phantom with SpheresPhantom having spheres with volumes ranging from 1.9ml (~1.5cm diameter) to 100ml (~5.7cm diameter) used for quantification studies1.9 ml11.0 ml63.0 ml100.0 ml10000 mlInitial Loading without BackgroundSpheres loaded with total of 341 MBq (9.2 mCi) of Y-90 chloride + EDTAY-90 assayed on Capintec CRC 15R using settings 55 (x10) for plastic syringe and 48 (x10) for glass vialsScanned with PET and then SPECT5.3 MBq2.8 MBq/ml

24.7 MBq2.2 MBq/ml106.6 MBq1.7 MBq/ml199.0 MBq2.0 MBq/ml0 MBqSpheres with Background0.9 MBq0.46 MBq/ml

4.1 MBq0.37 MBq/ml17.8 MBq0.28 MBq/ml33.3 MBq0.33 MBq/ml414.6 MBq0.04 MBq/mlOne week (2.6 half-lives) later, 414.6 MBq (11.2 mCi) of Y-90 chloride was loaded into water surrounding spheres as backgroundPhantom rescanned with SPECT and then PETSPECT ImagingSiemens Symbia T6 TruePoint SPECT/CTHigh-energy collimatorsSix contiguous energy windows 105285 keV128x128 matrix 4.8mm pixels, OSEM (Flash 3D) 6 subsets, 20 iterationsNo scatter correctionAttenuation correction from CT using center energy for each window

6Energy (keV)Y-90 Energy Spectrum6PET ImagingSiemens Biograph 6 extended FOV (21.6cm) LSO-based PET/CT

435650 keV window

Phantom imaged in one bed position

3D OSEM reconstruction, 3 iterations, 21 subsets

No TOF

No copper or lead filter to moderate bremsstrahlung count rate

CT used for attenuation correction77AnalysisSpherical VOIs for spheres and background regions defined on CT scan for each dataset

For PET quantification, images were reconstructed to obtain radionuclide concentration in Bq/ml with F-18 calibration and corrected for Y-90 positron fraction

For SPECT, the largest (100 ml) sphere was used for calibration in each scan

8SPECT 135165 keV Window

70 minute acquisition timeMIPSPECT 135165 keV Window10VOIVolume (ml)Est Total (MBq)True Total(MBq)Est Conc(MBq/ml)True Conc(MBq/ml)Error(%)12.01.13.00.571.58-63.9211.19.813.80.891.26-29.2361.654.459.80.860.95-9.1499.5111.7111.71.11.10Bkgd 10.030--Bkgd 20.050--SPECT 255285 keV Window

70 minute acquisition timeMIPSPECT 255285 keV Window12VOIVolume(ml)Est Total (MBq)True Total(MBq)Est Conc(MBq/ml)True Conc(MBq/ml)Error(%)12.01.13.00.591.58-62.4211.29.713.80.881.26-29.9362.253.959.80.860.95-9.1499.6111.7111.71.11.10Bkgd 10.040--Bkgd 20.040--Bkgd 30.100--PET No Background

40 minute acquisition time (equivalent to SPECT with decay)MIPPET No Background14VOIVolume(ml)Est Total (MBq)True Total(MBq)Est Conc(MBq/ml)True Conc(MBq/ml)Error (%)11.92.25.41.22.8-58.2211.115.824.51.42.2-35.6363.881.9105.81.31.8-22.64101.4154.4197.51.52.0-21.8Bkgd10.200--Bkgd 20.380--SPECT 135165 keV Window + Bkgd

120 minute acquisition timeMIPSPECT 135165 keV Window + Bkgd16VOIVolume(ml)Est Total (MBq)True Total(MBq)Est Conc(MBq/ml)True Conc(MBq/ml)Error(%)12.00.30.90.150.46-66.6211.43.14.00.280.37-23.8363.417.417.50.280.28-0.64100.432.632.60.330.330Total10000+1127.0461.0----144.5Bkgd10.190.04375.4Bkgd 20.120.04184.6Bkgd 30.090.04133.4SPECT 255285 keV Window + Bkgd

120 minute acquisition timeMIPSPECT 255285 keV Window + Bkgd18VOIVolume(ml)Est Total (MBq)True Total(MBq)Est Conc(MBq/ml)True Conc(MBq/ml)Error12.00.80.90.440.46-4.0211.43.44.00.300.37-17.0362.218.317.50.290.284.8499.532.632.60.330.330Total10000+1659.4461.0----260.1Bkgd10.170.04323.9Bkgd 20.140.04241.9Bkgd 30.140.04241.9PET + Background19

120 minute acquisition timeMIP19PET + Background20VOIVolume(ml)Est Total (MBq)True Total(MBq)Est Conc(MBq/ml)True Conc(MBq/ml)Error11.90.60.80.300.44-31.6211.23.33.80.290.35-14.6361.518.116.70.290.268.74100.335.031.10.340.3112.3Bkgd10.130.04245.7Bkgd 20.130.04245.7Bkgd 30.160.04314.8Estimated Activity vs. Truth21SPECT ImprovementsShown in previous talk

2222PET ImprovementsTime-of-flight

Shielding of low-energy bremsstrahlung?

More appropriate reconstructionBetter random coincidence modelingMethods for reducing bias at low activities for datasets with few counts

2323SummaryBoth PET and bremsstrahlung SPECT are usable for Y-90 imaging

SPECT with high-energy collimators has moderate resolution and suffers from partial volume effects for small sources but much higher countrate than PET

PET suffers from a low event rate, high background from bremsstrahlung, and significant positive bias in regions of low activity but has inherently higher resolution than SPECT

Both will likely be useful for quantitative Y-90 imaging if appropriate corrections are performed

24PET without Activity? 25

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