Hartmut F.-W. Sadrozinski, SCIPP

Beam Test for Proton Computed Tomography PCT

Loma Linda University Medical Center

Hartmut F.-W. Sadrozinski

Santa Cruz Inst. for Particle Physics SCIPP

UCSC Santa Cruz Institute of

Particle Physics

Florence & Catania

(aka Mapping out “The Banana”)

• The pCT Project

• Most likely Path MLP

• Beam Test Set-up

• Comparison with MLP

• Localization Accuracy

Hartmut F.-W. Sadrozinski, SCIPP

Authors

Loma Linda UMCReinhartd Schulte, MDVladimir Bashkirov, PhDGeorge Coutrakon, PhDPeter Koss, MS

Santa Cruz Institute for Particle PhysicsHartmut Sadrozinski, PhDAbe Seiden, PhDDavid C Williams, PhDJason 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

Why Proton CT?

• 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

Proton CT System (Final & prototype)

Hartmut F.-W. Sadrozinski, SCIPP

Comparison pCT - X-ray CT

52

2

~ Dd

E

b

a

Hartmut F.-W. Sadrozinski, SCIPP

Simulations: The most likely path (“banana”)

Measurement of entrance and exit anglesconstrain the most likely path

The most likely path of an energetic charged particle through a uniform medium

D C Williams Phys. Med. Biol. 49 (2004) 2899–2911

200 MeV Protons, 20 cm water, most likely, 1 and 2 path’

Goal of the Beam Test:

Verify the MLP Predictions

Hartmut F.-W. Sadrozinski, SCIPP

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 m. 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

First Data: Beam Profile

Measured Beam profileAngle-position correlation:

x = -0.005+0.0002*x/mm

y = -0.003+0.0002*y/mm

“Fuzzy”Source at L= 1/0.0002= 5m

Beam Divergence B = 0.005

Translate and rotate coordinates such that

entrance is at (0,0) with zero angle

Measure outside parameters: Displacement y

exit angle

Measure inside parameter: Displacement yl

in roving module vs. absorber depth

Pro

ton

Ang

le

Proton Position

Hartmut F.-W. Sadrozinski, SCIPP

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

Displacement

Exi

t Ang

le

Hartmut F.-W. Sadrozinski, SCIPP

Exit Displacement & Angle Correlations

Displacement in Roving Module is correlated with exit displacement Y

Displacement in Roving Module is anti-correlated with exit angle blue:

Dis

plac

emen

t in

Abs

orbe

r

Dis

plac

emen

t in

Abs

orbe

rExit Displacement Exit Angle

Hartmut F.-W. Sadrozinski, SCIPP

First Results: < 500 m Localization within Absorber

Displacement from incoming direction in the “Roving planes” as a function of exit displacement bins of 500 m (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 m vs. MLP width of 380 m

• Resolution ultimately limited by Beam Spread

-0.5-0.4-0.3-0.2-0.1

00.10.20.30.40.5

0 2 4 6 8 10 12 14 16 18 20

Depth inside Absorber [cm]

Dis

plac

emen

t [cm

]

RMS = 490um

MLP width = 380 um

Hartmut F.-W. Sadrozinski, SCIPP

Angle Cut improves Localization

0

0.05

0.1

0.15

0.2

0.25

0 5 10 15 20 25

Depth inside Absorber [cm]D

isp

lace

men

t [c

m]

0.018 rad0.036 rad0.00 rad

Displacement in the “roving” modules for an exit displacement of 2 mm, Select 3 narrow exit angle bins :Mean Mean + 1 Mean –1

Observe expected negative correlationResolution improves wrt no angle selection

pCT design validated: measure

Exit Angle Selection [rad]

Depth All 0.033 0.066 0.0 MLP

5 0.038 0.033 0.029 0.034 0.027

7.5 0.049 0.043 0.041 0.041 0.038

14 0.054 0.039 0.035 0.038 0.031

pCT design validated:

measure both exit displacement AND angle

with high precision

Hartmut F.-W. Sadrozinski, SCIPP

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