Towards Proton Computed Tomography L. R. Johnson, B. Keeney, G. Ross, H. F.-W. S

Towards Proton Computed Tomography L. R. Johnson, B. Keeney, G. Ross, H. F.-W. S

Towards Proton Computed Tomography L. R. Johnson, B. Keeney, G. Ross, H. F.-W. S

Gallo, Phil, Contributor has reference to this Academic Journal, PHwiki organized this Journal Towards Proton Computed Tomography L. R. Johnson, B. Keeney, G. Ross, H. F.-W. Sadrozinski, A. Seiden, D.C. Williams, L. Zhang Santa Cruz Institute as long as Particle Physics, UC Santa Cruz, CA 95064 V. Bashkirov, R. W. M. Schulte, K. Shahnazi Loma Linda University Medical Center, Loma Linda, CA 92354 Proton Energy Loss in Matter Proton Tomography / Proton Transmission Radiography Proton Transmission Radiography Data Proton Transmission Radiography MC Study Computed Tomography (CT) CT: Based on X-ray absorption Faithful reconstruction of patient’s anatomy Stacked 2D maps of linear X-ray attenuation Coupled linear equations Invert matrices in addition to reconstruct z-dependent features X-ray tube Detector array Proton CT: replaces X-ray absorption with proton energy loss reconstruct mass density (r) distribution instead of electron distribution Radiography: X-rays vs. Protons Attenuation of Photons, Z N(x) = Noe- m x Energy Loss of Protons, r NIST Data Low Contrast: Dr = 0.1 as long as tissue, 0.5 as long as bone Measure statistical process of X-ray removal Measure energy loss on individual protons Bethe-Bloch

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Negative Slope in the Bethe-Bloch Formula Relatively low entrance dose (plateau) Maximum dose at depth (Bragg peak) Rapid distal dose fall-off RBE close to unity Protons vs. X-Rays in Therapy Protons: Energy modulation spreads the Bragg peak across the malignancy X-rays: High entrance dose Reduced dose at depth Slow distal dose fall-off leads to increased dose in non-target tissue Milestones of Proton Computed Tomography R. R. Wilson (1946) Points out the Bragg peak, defined range of protons A. M. Cormack (1963) Tomography M. Goitein (1972) 2-D to 3-D, Simulations A. M. Cormack & Koehler (1976) Tomography, Dr 0.5 % K. M.Hanson et al. (1982) Human tissue, Dose advantage U. Schneider et al. (1996) Calibration of CT values, Stoichiometric method T. J. Satogata et al. (Poster M10-204) Reduced Dose of Proton CT compared to X-Ray CT

What is new in pCT Increased of Facilities with gantries etc. See the following talk by Stephen G. Peggs) 2 Ph.D. Theses at PSI in addition to Harvard Cyclotron (U. Schneider & P. Zygmanski) Existence of high b in addition to width detector systems as long as protons semiconductors high rate data acquisition ( > MHz) large-scale (6”wafers) fine-grained (100’s um pitch) Concerted simulation ef as long as t Exploitation of angular in addition to energy correlations Support of data analysis Optimization of pCT set-up (detector, energy, ) Dose calculation Potential of Proton CT: Treatment Planning X-ray CT use in proton cancer therapy can lead to large uncertainties in range determination Proton CT can measure the density distribution needed as long as range calculation. There is an expectation (hope) that with pCT the required dose can be reduced. Low Contrast in Proton CT Sensitivity Study: Inclusion of 1cm thickness in addition to density r at midpoint of 20cm H2O

Requirements as long as pCT Measurements Tracking of individual Protons requires Measurement of: Proton angle to much better than a degree Multiple Coulomb Scattering MCS1o Proton location to few hundred um Average Proton Energy to better than % In order to minimize the dose, the final system needs the best energy resolution! Energy straggling is 1- 2 %. Improve energy determination with statistics Issue: Dose D = Absorbed Energy / Mass N/A = Fluence ( as long as Voxel with diameter d = 1mm 105 protons of 200 MeV = 7 [mGy]) Dose vs. Voxel Size as long as pCT Measurements Define voxel of volume d3 Dose in voxel = Dv Take n =20cm/d settings Total dose D = n Dv Trade-off between Voxel size in addition to Contrast (Dr) to minimize the Dose Require 3s Significance Studies in Proton Computed Tomography Exploratory Study in Proton Transmission Radiography Silicon detector telescope Simple phantom in front Underst in addition to influence of multiple scattering in addition to energy resolution on image Theoretical Study (GEANT4 MC simulation) Evaluation of MCS, range straggling, in addition to need as long as angular measurements Optimization of energy Collaboration Loma Linda University Medical Center – UC Santa Cruz

Exploratory Proton Radiography Set-up Degraded down to 130 MeV by 10” wax block Proton Beam from Loma Linda University Medical Ctr @ 250 MeV Object is aluminum annulus 5 cm long, 3 cm OD, 0.67 cm ID Very large effects expected, x = rl = 13.5 g/cm2 Traversing protons have 50 MeV, by-passing protons have 130 MeV Silicon detector telescope with 2 x-y modules: measure energy in addition to location of exiting protons Silicon Detector Telescope GLAST Readout 1.3 ms shaping time Binary readout Time-over-Threshold TOT Large dynamic range Simple 2D Silicon Strip Detector (SSD) Telescope of 2 x-y modules built as long as Nanodosimetry 2 single-sided SSD / module measure x-y coordinates GLAST Space Mission developed SSD 194 mm pitch, 400 mm thickness Time-Over-Threshold ~ Energy Transfer TOT charge LET Digitization of position (hit channel) in addition to energy deposit (TOT)

Calibration of Proton Energy vs. TOT Derive energy resolution from TOT vs. E plot Good agreement between measurement in addition to MC simulations Image of Al Annulus Subdivide SSD area into pixels Strip x strip 194um x 194um 4 x 4 strips (0.8mm x 0.8mm) Image corresponds to average energy in pixel Energy Resolution => Position Resolution Slice of average pixel energy in 4×4 pixels (need to apply off-line calibration!) Clear profile of pipe, but interfaces are blurred

Multiple Scattering: Migration Protons scatter OUT OF target (not INTO). Scatters have larger energy loss, larger angles, fill hole, dilute energy Image Features: Washed out image in 2nd plane (30cm downstream) Energy diluted at interfaces (Fuzzy edges, Large RMS, Hole filled in partially) Migration of events are explained by Multiple Coulomb Scattering MCS GEANT4 MC: Use of Angular In as long as mation Angular distributions well understood Si Telescope allows reconstruction of beam divergence in addition to scattering angles Select 2 Areas in both MC in addition to Data A = inside annulus : Wax + Al B = outside annulus : Wax only GEANT4 MC: Migration Protons entering the object in front face but leaving it be as long as e the rear face Beam profile in slice Energy of protons entering front face Migration out of object

GEANT4 MC: Use of Angular In as long as mation Less Migration Angular Cut at MCS of the Wax Sharp Edges (Energy Average) Sharp Edges (Energy RMS) Angular cut improves the contrast at the interfaces Conclusions Present status of pCT: Long tradition, increased interest with many new proton accelerators (see next talk by Stephen G. Peggs) pCT will be useful as long as treatment planning (reconstruction of true density distribution) Potential dose advantage wrt X-rays ( see Poster M10-204 by Satogata et al. ) Use of GEANT4 simulation program aids in planning of experiments (correlation of energy in addition to angle, “migration”) (see Poster M6-2, L. R. Johnson et al.) Our future plans: Optimization of beam energy Investigation of optimal energy measurement method Dose – contrast – resolution relationship on realistic phantoms

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