Beam Test for Proton Computed Tomography PCT

Transcription

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 Florence & Catania Loma Linda University Medical Center UCSC Santa Cruz Institute of Particle Physics

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)

3 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

4 Proton CT System (Final & prototype)

5 Comparison pct - X-ray CT D ~ 2 σ E 2 ρ d a b

6 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) Measurement of entrance and exit angles constrain the most likely path 200 MeV Protons, 20 cm water, most likely, 1 σ and 2 σ path Goal of the Beam Test: Verify the MLP Predictions

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 µm. 2 nd rotated by 90 o 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

8 Measured Beam profile First Data: Beam Profile Angle-position correlation: θ x = *x/mm θ y = *y/mm Fuzzy Source at L= 1/0.0002= 5m Beam Divergence σ B = Proton Angle Proton Position Translate and rotate coordinates such that entrance is at (0,0) with zero angle Measure outside parameters: Displacement y Measure inside parameter: exit angle θ Displacement yl in roving module vs. absorber depth

9 MCS at Work Correlation between exit displacement and angle Exit Angle Displacement 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

10 Exit Displacement & Angle Correlations Displacement in Absorber Displacement in Absorber Exit Displacement Displacement in Roving Module is correlated with exit displacement Y Exit Angle Displacement in Roving Module is anti-correlated with exit angle blue:

11 First Results: < 500 µm Localization within Absorber Displacement [cm] RMS = 490um MLP width = 380 um Depth inside Absorber [cm] Displacement from incoming direction in the Roving planes as a function of exit displacement bins of 500 µm (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 µm vs. MLP width of 380 µm Resolution ultimately limited by Beam Spread

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 σ Mean 1 σ Observe expected negative correlation Resolution improves wrt no angle selection Displacement [cm] rad rad 0.00 rad pct design validated: measure Exit Angle Selection [rad] Depth All MLP Depth inside Absorber [cm] pct design validated: measure both exit displacement AND angle with high precision

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