Prostate probe with SPECT technique NSS – MIC November 5 - KnoxvilleF. Garibaldi- INFN – Roma1 – gr. Coll. ISS  the medical problem  the proposal  Layout  Multimodality  SiPM/electronics  summary and outlook 1

Radionuclides imaging techniques Patient injected with radioactive drug. Drug localizes according to its metabolic properties. Gamma rays, emitted by radioactive decay, that exit the patient are imaged. 1.Collimator Only gammas that are perpendicular to imaging plane reach the detector 2.Scintillator Converts gammas to visible light 3.Photodetector Convert light to electrical signal 4.Readout Electronics Amplify electrical signal and interface to computer 5.Computer decoding procedure Elaborate signal and gives image output

PET Compton Camera mechanical collimation Multi pinhole

Single photon techniques - simple(r) - cheape(r) - extending the radiotracers available - dual tracer  looking at two different biological processes pros cons - efficiency - spatial resolution

Compton Prostate Imaging Probe Internal Compton ProbeExternal Compton Probe

Predicted Internal Probe Performance 4mm Point-to-Point, 1cm from probe (Monte Carlo simulation + ML reconstruction) 141keV 171keV245keV 364keV 511keV Imaging Distance10 cm Compton Probe High-Sensitivity Collimator High-Resolution Collimator Efficiency Resolution 1.8e mm 1.11e mm 4.00e mm Comparison with SPECT for In-111

Relative Uptake of In-111 Prostascint OrganRelative Uptakes Prostate1.0 Liver2.0 Blood1.5 Bone0.7 Kidney1.0 Spleen1.0 Bladder0.6 Rectum0.4 Testes0.6 Averaged from three In-111 Prostascint SPECT scans

Conventional SPECT Reconstructions 5:110:115:120:1 w / tumor bkgd 171 and 245 keV, 8.8M events / 40 slices Spatial resolution ~15mm FWHM Prostate

Compton Prostate Probe Reconstructions 5:110:115:120:1 w / tumor bkgd 245 keV only, 1.2 million events, 8mm lesion Prostate Spatial resolution ~2mm FWHM

Internal Detector Details 10–12 layers of 1mm thick Si detectors + position and orientation sensor Exploded View Assembled Unit

Compton Probe Promising but Challenging First detector –Energy resolution – largely addressed –Timing resolution – still an issue –Packaging – solvable Second detector –Countrate capability – solvable –Cost – always an issue System –Image reconstruction – solvable

Detector Packaging Unfolded energy spectrum “Raw” energy spectrum Use Tape Automated Bonding (TAB) (Very thin kapton tape with aluminum traces) Kapton microcables Detector VATA ASIC Kapton “hybrid” board

Timing Desired time resolution <10ns FWHM Poor timing from Si is evident Slower signal generation from events near backplane Large range of pulse-height coupled with leading-edge trigger is a big issue  time-walk Signal generation depends on 3D interaction position and recoil electron direction  time-jitter Signal generation at two biases for three depths BGO-Silicon timing spectrum for 511 keV source

How Challenges Affect Performance Consider anticipated countrate with In-111 Prostascint (from Monte Carlo simulations): –~4 Mcps on second detector –~40 kcps on scattering detector –50 ns time window for present Si detectors (may need to be even larger) C random = 2 x 4x10 6 x 4x10 4 x 50x10 -9 = 16,000 cps ! C true was only ~10 kcps (or less) Performance dominated by randoms! Energy sum window can be used to reject randoms but only if the second detector also has good energy resolution

Single photon Compton camera ( N. Clinthorne. Michigan )

External Multipinhole Alternative External probes will have small FOV and limited-angle tomography but… SPECT/CT can identify prostate region Probe can be computer-steered to image desired FOV Conventional SPECT can be used to “complete” probe data

Endorectal Multipinhole? 30mm ~15mm Some tomographic capability Requires high detector resolution (0.5–1 mm + depth-of-interaction) High enough efficiency and resolution?

W. Moses – Rome workshop 2005

111 In-ProstaScint is not a good radiotracer but a new one proposed by M. Pomper looks promising. Radionuclides Single photon The single photon endorectal probe provides 2D imaging. We have to try to have 3 D images ( using multipinhole collimation and/or adding up a SPECT tomograph (spatial resolution would be dominated by the small probe (see later, the PET case ))

our proposal -insert scintillator pixels into square holes of the collimator  better performances (spatial resolution (?) and sensitivity (thicker scintillator)) -using diverging collimator  better performances (reducing scan time) -using multipinhole collimation  better performances (increasing sensitivity, tomographic recinstruction)

New radiotracers coming soon (M. Pomper, Johns Hopkins) Radiotracers available for SPECT and PET (from “New agents and Techniques for Imaging prostate cancer” A. Zahreer, S. Y. Cho, M. Pomper”, to be published on JNM ) SPECT: Prostascint, Bombesyn, 99mTechnetium nanocolloid (limphonodes), other coming soon … PET C—11 Choline, F-18-Choline, Ga-68 Dotabomb (Hofmann (Rome workshop)) many others coming… (collaboration with Johns Hopkins for testing in ISS (mice models for prostate available) and/or at JHU) 22