1. Beam Test for Proton Computed Tomography PCT
(aka Mapping out “The Banana”)
Hartmut F.-W. Sadrozinski
Santa Cruz Inst. for Particle Physics SCIPP
The pCT Project
Most likely Path MLP
Beam Test Set-up
Comparison with MLP
Localization Accuracy
UCSC Santa Cruz Institute of Particle Physics
Loma Linda University Medical Center
Florence & Catania
Hartmut F.-W. Sadrozinski, SCIPP

2. Authors Loma Linda UMC Reinhartd Schulte, MD Vladimir Bashkirov, PhD
George Coutrakon, PhD
Peter Koss, MS
Santa Cruz Institute for Particle Physics
Hartmut Sadrozinski, PhD
Abe Seiden, PhD
David C Williams, PhD
Jason Feldt (grad. Student)
Jason Heimann (undergrad student)
Dominic Lucia (undergrad student)
Nate Blumenkrantz (undergrad student)
Eric Scott (undergrad student)
Florence U.
Mara Bruzzi, PhD
David Menichelli, PhD
Monica Scaringella (grad student)
INFN Catania
Pablo Cirrone, PhD
Giacomo Cuttone, PhD
Nunzio Randazzo, PhD
Domenico Lo Presti, Engineer
Valeria Sipali (grad student)
Hartmut F.-W. Sadrozinski, SCIPP

3. Why Proton CT? Goal of pCT Collaboration
Major advantages of proton beam therapy:
Finite range in tissue (protection of critical normal tissues) since cross section fairly flat and low away from peak
Maximum dose and effectiveness at end of range (Bragg peak effect)
Major uncertainties of proton beam therapy:
range uncertainty due to use of X-ray CT for treatment planning (up to several mm)
patient setup variability
Goal of pCT Collaboration
Develop proton CT for applications in proton therapy
Hartmut F.-W. Sadrozinski, SCIPP

4. Proton CT System (Final & prototype)
Hartmut F.-W. Sadrozinski, SCIPP

5. Comparison pCT - X-ray CT
Hartmut F.-W. Sadrozinski, SCIPP

6. Verify the MLP Predictions
Simulations: The most likely path (“banana”)
The most likely path of an energetic charged particle through a uniform medium
D C Williams Phys. Med. Biol. 49 (2004) 2899–2911
Measurement of
entrance and exit angles
constrain the
most likely path
200 MeV Protons, 20 cm water, most likely, 1 s and 2 s path’
Goal of the Beam Test:
Verify the MLP Predictions
Hartmut F.-W. Sadrozinski, SCIPP

7. Beam Test setup
In and out telescopes measure entrance and exit location and angle
“Roving” module in between absorbers measures the 2-D displacement wrt beam = “banana”
Move roving module through the segmented absorber
GLAST BT 97 Silicon Telescope
single-sided SSD, pitch = 236 mm. 2nd rotated by 90o
GLAST GTFE32 readout chips, 32 channels each, serial data flow.
Replace large scale GLAST readout (VME, Vxworks software) by commercial FPGA and NI 6534 PCI card
Hartmut F.-W. Sadrozinski, SCIPP

8. First Data: Beam Profile
Measured Beam profile
Angle-position correlation:
qx = *x/mm
qy = *y/mm
“Fuzzy”Source at L= 1/0.0002= 5m
Beam Divergence sB = 0.005
Proton Angle
Proton Position
Translate and rotate coordinates such that
entrance is at (0,0) with zero angle
Measure outside parameters: Displacement y
exit angle q
Measure inside parameter: Displacement yl
in roving module vs. absorber depth
Hartmut F.-W. Sadrozinski, SCIPP

9. MCS at Work Correlation between exit displacement and angle
Without Absorber
Map out Beam Dispersion
Limited by Beam Spread
With Absorber
Angular Spread given by multiple scattering ~ 3 degrees
Strong correlation between angle and displacement due to multiple scattering
Exit Angle
Displacement
Hartmut F.-W. Sadrozinski, SCIPP

10. Exit Displacement & Angle Correlations
Displacement in Absorber
Displacement in Absorber
Exit Displacement
Exit Angle
Displacement in Roving Module is correlated with exit displacement Y
Displacement in Roving Module is anti-correlated with exit angle blue:
Hartmut F.-W. Sadrozinski, SCIPP

11. First Results: < 500 mm Localization within Absorber
Displacement from incoming direction in the “Roving planes” as a function of exit displacement bins of 500 mm (all angles).
Analytical calculation of the most likely path MLP (open symbols: the size of the symbol is close to the MLP spread).
Good agreement data - MLP,
but systematically growing difference with larger displacements: need to incorporate absorber-free distance (M.C.)
Resolution inside Absorber better than 500 mm vs. MLP width of 380 mm
Resolution ultimately limited by Beam Spread
RMS = 490um
MLP width = 380 um
Hartmut F.-W. Sadrozinski, SCIPP

12. Angle Cut improves Localization
Displacement in the “roving” modules for an exit displacement of 2 mm,
Select 3 narrow exit angle bins :
Mean
Mean + 1 s
Mean –1 s
Observe expected negative correlation
Resolution improves wrt no angle selection
pCT design validated: measure
pCT design validated:
measure both exit displacement AND angle
with high precision
Hartmut F.-W. Sadrozinski, SCIPP

13. pCT Beam Test Conclusions
Si tracker affords high resolution position and angle measurement
First results show localization within phantom to better than 400 um
Simple analysis confirms prediction of MLP on the < 200 um level
(improvement expected when air gaps are included)
Data await detailed comparison with simulations using GEANT4 and analytical “banana” (INFN, SLAC and Japanese Geant4 groups)
------>Poster J03-25
Improvements for Tracker:
Reduce absorber-less gap around “roving module”
Increased precision of input parameters (entrance angle) needed to correct for beam divergence
Next step: image NON-uniform density phantom using the energy loss measurement in the calorimeter
Hartmut F.-W. Sadrozinski, SCIPP