View
0
Download
0
Category
Preview:
Citation preview
Real-time monitoring of ion ranges
J.M. Létangon behalf of IPNL and CREATIS groups (Lyon, France)
2nd Workshop on Hadron Beam Therapy of CancerErice, Sicily, Italy
May 20, 2011 - May 27, 2011
• Two facilities for C-ion facilities will be available in 2015-16● Caen (Archade, IBA-C400 cyclotron): fundamental research● Lyon (ETOILE center): clinical facility and translational research
PRRHRhône-Alpes Research Program in Hadrontherapy
6. Simulations for the treatment plan / dose deposition D. Sarrut, N. Freud
Medical
Mathematics
Physics
Radiobiology
Dosimetry
Imaging
Technology
1. Medical Project (evaluation) J. Balosso, P. Pommier
2. Medico-economical simulations P. Pommier
3. In silico modelling of treatments B. Ribba
4. Basic data acquisition, online control D. Dauvergne
5. Hadronbiology, radiobiological effects of carbon ions C. Rodriquez, M. Beuve and N. Foray
7. Movement and deformation of tumours B. Shariat, D. Sarrut
8. Technological developements (gantry) collab. CEA, M. Bajard
Research topics of PRRH(coordinators: Prof. J-M. Moreau, Prof. J. Remillieux)
Outline of the talk
1. Context of the research
2. Rationale of real-time monitoring
3. Preliminary development (TOF)
4. Measurements
5. Simulations and Physics models
6. Camera designs
7. Reconstruction issues
8. TPS issues
Rationale of real-time monitoring
With Ion-Beam Therapy:
1. The dose is more conformational to the tumor
2. but uncertainties exist
● stoichiometric calibration (~3% in ion range)
● patient motion intra and inter fractions
► Need for a feedback loop to stop treatment if deviations occur
Ion range vs Dose
In-situ 1-D Camera is sufficient for real-time ion range monitoring of each beam spot (information in the plane normal to the beam can be integrated).
Dose calculations are not necessary for real-time monitoring, it is an off-line issue.
511 keV γ-rays vs prompt photons
Statistical photons Giant Dipole Resonance Nucleon-nucleon Bremsstrahlung
12C 310 MeV/u in water
Le Foulher 2010
What is the best particle to monitor treatment?
► β+ emitters cannot be used because of time constraints
► several 2ndary particles (γ, n, p...) are instantly emitted and correlated to the Bragg peak
► Choice may depend on the incident particle type (p, C-ion...)
Choice for real-time monitoring
Outline of the talk
1. Context of the research
2. Rationale of real-time monitoring
3. Preliminary development (TOF)
4. Measurements
5. Simulations and Physics models
6. Camera designs
7. Reconstruction issues
8. TPS issues
Many 2ndary particles (esp. for C-ion beam) out of the patient
► Background rejection welcome (e.g. neutrons)
► Need of a beam tagging device for TOF measures
► Knowledge of the transversal position of each ion would ease 1D reconstruction
Development of an Hodoscope
Preliminary development
• 1mm2 square fibers (2 planes H+V x 32 fibers): spatial resolution• Light transmission: optic fibers• coupled to flat panel PM : Hamamatsu H8500 64 channels
Timing resolution: 350 ps rmsFluence capability of fibers: >1012 ions/cm2
Scintillating fibers hodoscope (1st proto)
Fluence(1012 ions / cm2)
Threshold(mV)
Efficiency (%)
0.7 30 95
230 65
15 90
4
15 85
No gain in efficiency when:● decreasing the threshold● increasing the HT
To Do:– Measurement of the
maximum count rate– Development of a
hodoscope coupled to a MCP-PMT
4020 60 Charge (pC)
charge spectrum at the flat-panel output with a beam of 12C ions at 75 MeV/u
Scintillating fibers hodoscope (1st proto)
Ageing:> 1 year on clinical condition
Outline of the talk
1. Context of the research
2. Rationale of real-time monitoring
3. Preliminary development (TOF)
4. Measurements
5. Simulations and Physics models
6. Camera designs
7. Reconstruction issues
8. TPS issues
Several sets of C-ion experiments have been carried out
● Low energy [GANIL]: ✗ 13C-ion @ 73 MeV/u✗ 12C-ion @ 95 MeV/u
● High energy [GSI]: ✗ 12C de 292 MeV/u✗ 12C de 310 MeV/u
Prompt-γ experiments
Prompt-γ experiments: Setup
Setup● Collimated scintillators @ 90°● Target on a translation table
GANIL TOF measurements with BaF2 13/3
3
Prompt-γ experiments: 2-D TOF spectrum
● Broad prompt-γ spectrum● Time and energy window for better background removal
12C at 95 MeV/u
Longitudinal Position (mm)
Num
ber
o f g
amm
a /
ion
No selectionTime of flight (2-4 ns)
E. Testa et al., Appl. Phys. Lett. 93, 093506 (2008)
beam
Prompt-γ experiments: Feasibility studyPrompt-γ emission depth scans
12C at 95 MeV/u
Longitudinal Position (mm)
Num
ber
o f g
amm
a /
ion
No selectionTime of flight (2-4 ns)
E. Testa et al., Appl. Phys. Lett. 93, 093506 (2008)
beam
Prompt-γ experiments: Feasibility studyPrompt-γ emission depth scans
1st evidence with C-ion of correlation between prompt-γ emission and ion range
prompt-γ yield = 0.3 per C-ion (Edep
>2MeV)
Pulse Shape Discrimination – BC501
Prompt-γ experiments: Neutron study
GANIL
BC
501
BaF
2
Neutron uncorrelated in time and position with C-ions
No apparent range verification with n
18/33
Prompt-γ experiments: Neutron study
Outline of the talk
1. Context of the research
2. Rationale of real-time monitoring
3. Preliminary development (TOF)
4. Measurements
5. Simulations and Physics models
6. Camera designs
7. Reconstruction issues
8. TPS issues
GANIL – 13C@73 MeV/u (PMMA target)
Prompt-γ counting rate: simulations overestimate by a factor of ~ 12with Binary Cascade (BIC) nuclear collision model
F. Le Foulher IEEE TNS 2010
GANIL – 12C@95 MeV/u (PMMA target)
E>2 MeV
Prompt-γ simulations: Early comparisons
Monte Carlo toolbox Geant4 v9.1
GANIL – 13C@73 MeV/u (PMMA target)
Prompt-γ counting rate: simulations overestimate by a factor of ~ 12with Binary Cascade (BIC) nuclear collision model
F. Le Foulher IEEE TNS 2010
GANIL – 12C@95 MeV/u (PMMA target)
E>2 MeV
Prompt-γ simulations: Early comparisons
Monte Carlo toolbox Geant4 v9.1
A complete tuning (identification free parameters) of Geant4 nuclear models for hadrontherapy domain is required
3 stages:
Nuclear CollisionBinary Cascade, QMD, Bertini Cascade
EquilibrationPrecompound Model, Preequilibrium Model
DeexcitationMultifragmentation, Evaporation, Fermi Break-Up, PhotonEvaporation
Prompt-γ simulations: Geant4 nuclear model
QMD tuning is a complicated problem• Multiparameter• Some parameters have some degrees of freedom
(within physical constraints)• Not always easy to predict the influence of modifications
(dose, β+ emitters, other 2ndary particles...)• Not much documented• Ultimate check (Photon Yield in the Detector) is CPU demanding
2 'free' parameters have been identified for prompt-γ yield:● Cluster size● Particle wavepacket width
Prompt-γ simulations: QMD nuclear collision
G. Dedes unpublished 2011
● QMD cluster size has a straightforward influence:✗ Lower maximum distance ✗ Smaller clusters ✗ Smaller nuclei ✗ Lower excitation Energy ✗ Lower yields
● but there are some physical limits due to nucleons size and the impact on light fragment yield will have to be investigated
Prompt-γ simulations: QMD cluster size
G. Dedes unpublished 2011
Prompt-γ simulations: QMD cluster size
Clear improvements but not sufficientG. Dedes unpublished 2011
Shape is better reproduced by QMD 2fm
As expected, increase in lighter fragments with decreasing clustering maximum distance
Prompt-γ simulations: QMD cluster size
G. Dedes unpublished 2011
2ndary fragment distributions
Lighter fragments have lower excitation energies and produce less photons:
Prompt-γ spectrum change
Prompt-γ simulations: QMD cluster size
G. Dedes unpublished 2011
Lighter fragments have lower excitation energies and produce less photons:
Prompt-γ spectrum change
Prompt-γ simulations: QMD cluster size
G. Dedes unpublished 2011
Geant4 nuclear models are indeed tunable for the hadrontherapy domain. Further investigations are needed (HP neutrons, De-Excitation Handler, Photon Evaporation...)
Outline of the talk
1. Context of the research
2. Rationale of real-time monitoring
3. Preliminary development (TOF)
4. Measurements
5. Simulations and Physics models
6. Camera designs
7. Reconstruction issues
8. TPS issues
Collimated prompt-γ camera
M. Testa REBS 2010
Components:- Hodoscope: ion tagging (time and position) with scintillating fibres
(delayed stop signal)- Collimation: vertical slits (W)- Detectors: LYSO (start signal) - TOF: γ-n discrimination (resolution: 1ns)
Polychromatic prompt-γ spectrum (exponential fit)
Line segment prompt-γ source(to simulate the prompt-γ emission points along the ion range)
The collimator geometry is a trade-off between detection efficiency and spatial resolution (S=T=3mm)
Simulation set-up
M. Testa REBS 2010
Collimated prompt-γ camera: design
Q/2
22 mm
25 mm
28 mm
d
Q/2
M. Testa REBS 2010
Collimated prompt-γ camera: spatial resolution
3 detection profiles (shift 3mm) 11 detection profiles (shift 1mm)
Quantitative evaluation of the spatial resolution:
fit erf, error function (inflection point)
Spatial resolution RCam: minimum detectable shift in source edge displacement
Spatial resolution driven by the collimator (around 2mm for a 3mm slit)and by the number of detectors for a given FOV (detection solid angle)
( )DetCollCam RRfuR ,=
M. Testa REBS 2010
Collimated prompt-γ camera: spatial resolution
On-going work of F. Roellinghoff (PhD@CPO with IBA) of collimated and slit cameras
● Measured prompt-γ yields:
● ~ 2×10-7 γ ion-1 (1 detector, field of view ~ 3 mm)
● ~ 1 to 2×10-7 γ ion-1 · msr-1 · mm-1
● Typical carbon treatment : ● ~ 2×107 ions per energy slice (average)● ~ 4 γ for 1 slice in 1 detector 3mm x 5cm
● Multi-detector ● 25 crystals at a same FOV (depth)
→ size equivalent to GSI-PET
● Yield per energy slice:
● Along ion range ~ 100 counts / FOV
● Beyond ion range ~ 30 counts / FOV
→ resolution on Bragg peak position ~ 3 - 4 mm (MC simulations)
Pencil beam scanning
Collimated prompt-γ camera: clinical conditions
2ble scattering Compton camera: setup
M.-H. Richard TNS 2011
Compton cone completely defined by● 2 scattering + ● 1 partial absorption events
Fragmentation point reconstruction:
simple line-cone intersection
● incident C-ion: hodoscope● hypothesis: no straggling
M.-H. Richard TNS 2011
2ble scattering Compton camera: MC simulations
● TOF for (n + scattered-γ) background rejection:
no shielding
● Si-scatterer to limit Doppler broadening
● Point source (broad spectrum)
Prompt-γ energy spectrum
2ble scattering Compton camera: FWHM
True events
Edep
< 2MeV
e- escape from the 1st scatterer (MIP)
FWHM 6mm
FWHM 30mm
Bad events
2ble scattering Compton camera: FWHM
True events
Edep
< 2MeV
e- escape from the 1st scatterer (MIP)
FWHM 6mm
FWHM 30mm
Bad events
Spatial resolution (6mm) acceptable but low detection efficiency (10-5)
Scatterer stack Compton camera: setup
F. Roellinghoff NIMA 2011
Based on MC simulations: from all events in the absorber, 75% correspond to total absorption in a 1in LYSO for a typical prompt-γ spectrum
● most single scattering events are reconstructible● higher detection efficiency for the same scatterer equivalent Si-thickness
F. Roellinghoff NIMA 2011
Scatterer stack Compton camera: simulations
● 10 Silicon strip detector (2mm thickness)● 1in LYSO absorber● Point source (broad spectrum) at 10cm from the 1st scatterer● Line-cone reconstruction
F. Roellinghoff NIMA 2011
Scatterer stack Compton camera: PSF
Spatial resolution (8.3mm) still acceptable and higher (x25) detection efficiency (2.5x10-4)
Scatterer stack Compton camera: Proton beam
Detection Efficiency
FWHM
scatterer limitscatterer limit
FWHM and DE deteriorate when the lateral position of emission
point along the ion range is away from the camera center
Study the influence of the fragmentation point lateral position(Compton camera centered in front of Bragg peak)
160MeV proton beam upon a water phantom (9x9x20 cm3)
Scatterer stack Compton camera: p@160MeV
Reconstructed pointsEmission points
Comparison of γ profiles
Reconstructed profile:
PSF(pos)
*[D
E(pos) x prompt-γ_profile]
Scatterer stack Compton camera: p@160MeV
Reconstructed pointsEmission points
Comparison of γ profiles
Reconstructed profile:
PSF(pos)
*[D
E(pos) x prompt-γ_profile]
More advanced Compton reconstruction techniques are required
Angular Resolution Measure
Scatterer stack CC by-product: SPECT imaging
M.-H. Richard unpublished 2011
Reconstruction algorithm necessary (no hodoscope)
Detection efficiency:● 0.05% @ 300keV● 0.1% @ 511keV● 0.09% @ 1MeV
Proton Vertex Imaging for C-ion beams
Idea:Use 2ndary protons to monitor the C-ion range
Is the proton Statistics high enough for ion-range monitoring?
P. Henriquet PhD 2011
Secondary proton detection
[GANIL]
Experimental detection rate :2.41 x 10-5 proton/12C/msr
Simulated detection rate (Geant4) :2.51 x 10-5 proton/12C/msr
Proton Vertex Imaging: Measurements
P. Henriquet PhD 2011
Good agreement (~4%)
20 °
10 cm Tracker
p12C
Proton Vertex Imaging: 1st simulated setup
P. Henriquet PhD 2011
● C-ion@200MeV/u● 10cm PMMA target● Si-tracker @ +/-20° Trade-off between proton straggling (minimum at 0°) / reconstruction uncertainty (minimum at 90°)
Incident 12C(beam hodoscope)
Reconstructed vertex Segment S (of lenght d)
Single mode
Coincidence mode
Reconstruction modes:
● Single (with hodoscope)● Coincidence
Proton Vertex Imaging: 1st simulated setup
P. Henriquet PhD 2011
Single
Coincidence
Depth (mm)
C-ion@200MeV/u10cm PMMA target
Statistics:106 primary C-ion
Single coincidence: higher statistics and better ion range discrimination
Depth-vertex profiles
Proton Vertex Imaging: "Clinical" setup
P. Henriquet PhD 2011
Target:● 3mm cranium bone● 25cm sphere (cervical tissue)
2 Detector pairs:● Pixellated Si-planes (10x10cm2)● +/-20° angle @ 30 & 35 cm
12C-ion beam:● 100 to 300MeV/u● 106 primary particles
(NB: about 107 C-ion / energy slice for 1GyE in a 120cm3 tumor volume)
Proton Vertex Imaging: "Clinical" setup
P. Henriquet PhD 2011
Depth (mm)
Reconstructed vertices
Generated vertices
Depth-Vertex profiles
Reconstructed vertex profile drop is correlated to ion range [150 - 300MeV/u]
Proton Vertex Imaging: "Clinical" setup
P. Henriquet PhD 2011
Depth (mm)
Reconstructed vertices
Generated vertices
Depth-Vertex profiles
Reconstructed vertex profile drop is correlated to ion range [150 - 300MeV/u]
Proton vertex imaging is a promising technique. Further investigations are needed
Outline of the talk
1. Context of the research
2. Rationale of real-time monitoring
3. Preliminary development (TOF)
4. Measurements
5. Simulations and Physics models
6. Camera designs
7. Reconstruction issues
8. TPS issues
3D Compton reconstruction
Analytical inversion formula Iterative List-mode Maximum Likelihood Expectation-Maximization
(LM-MLEM)
Status:● Line-cone reconstruction simple but limited● Hodoscope must be available (pb for SPECT)
2 research themes are investigated:
Analytical 3D Compton reconstruction
V. Maxim Inverse Problems 2009
Compton projection Pf definition:
V. Maxim Inverse Problems 2009
Inversion formula:
Analytical 3D Compton reconstruction
Fourier transform of the 2D Radon transformof the Compton projections
Exact Analytical inverse Compton transform exists!
Bessel function
Scattering probability
Analytical 3D Compton reconstruction
● Point γ source● Broad spectrum● 1.3 x 105 events
NB axial = plane normal to the beam
Real detector(energy and spatial resolutions)
Ideal detector (Δx=ΔE=0): projections truncation artefacts
Axial slicesTransverse slices
Application to the proposed scatterer-stack Compton camera
No axial resolution with the scatterer-stack Compton camera setup
FWHM = 6mm(transverse)
Analytical 3D Compton reconstruction
● Point γ source● Broad spectrum● 1.3 x 105 events
NB axial = plane normal to the beam
Real detector(energy and spatial resolutions)
Ideal detector (Δx=ΔE=0): projections truncation artefacts
Axial slicesTransverse slices
Application to the proposed scatterer-stack Compton camera
No axial resolution with the scatterer-stack Compton camera setup
FWHM = 6mm(transverse)
Limited applicability with one single CC(use as initialisation of an iterative reconstruction)
Outline of the talk
1. Context of the research
2. Rationale of real-time monitoring
3. Preliminary development (TOF)
4. Measurements
5. Simulations and Physics models
6. Camera designs
7. Reconstruction issues
8. TPS issues
TPS: Prior computation of detector response
The real-time monitoring (feedback loop) should be carried at the detector level
The detector signature must be pre-computed from the optimized DICOM RT-plan
Simple distance measures must be developped to trigger the feedback loop
Robustness issues must be taken into account
TPS needs:● a flexible optimization inverse planning SW● to optimize at the same time entry channels & fluences w.r.t.
● the prescribed dose,● plan uncertainties,● the way the ion range will be monitored
Development of a Genetic Algorithm-based TPS
Genetic Algorithm-based TPS
F. Smekens PhD 2011
OAR PTV
C-shape model
3000 beams after10000 generations
50 initial beams
● Continuous coding (angles and target points)
● Variable length (nr of beams)
128x128x107 voxels (1mm)
Genetic Algorithm-based TPS
F. Smekens PhD 2011
Application to CT data
200 beams (random pos+ang)
3000 beams (14000 generations)128x128x107 voxels (1mm)
Genetic Algorithm-based TPS
F. Smekens PhD 2011
Application to CT data
To do: include robustness and monitoring issues
Conclusions
Collaborators: IPNL: M. Bajard, M. Chevallier, D. Dauvergne, G. Dedes, S. Deng,
P. Henriquet, J. Krimmer, F. Le Foulher, C. Ray, M.-H. Richard, E. Testa, M. Testa
CREATIS: N. Freud, X. Locajono, V. Maxim, R. Prost, F. Roellinghoff, F. Smekens
Research program supports:● PRRH ETOILE (CPER 2007-2013)● GDR MI2B (CNRS-IN2P3)● Project ANR Gamhadron (2010-2013)● FP7 Collaboration project ENVISION (2010-2013)● FP7 ITN project ENTERVISION (2011-2014)
Real-time monitoring of ion-range seems accessible, several solutions are being investigated, but many developments are still required before translating to clinic.
Recommended