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Geometrical study of the optimum PET detector for monitoring

Geometrical study of the optimum PET detector for monitoring. I. Torres- Espallardo , P. Solevi , J. E. Gillam , J. F. Oliver, G. Llosá , M. Trovato , C. Solaz , C. Lacasta and M. Rafecas IFIC (Univ. Valencia/CSIC), Spain. Index.

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Geometrical study of the optimum PET detector for monitoring

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  1. Geometrical study of the optimum PET detector for monitoring I. Torres-Espallardo, P. Solevi, J. E. Gillam, J. F. Oliver, G. Llosá, M. Trovato, C. Solaz, C. Lacasta and M. Rafecas IFIC (Univ. Valencia/CSIC), Spain

  2. Index • „Evaluation of RPC-based PET appliedto in-beam HT monitoring“ – Review status (IT). • Geometricaloptimizationforcrystal-based PET dedicatedto HT monitoring (IT). • Novel PET design: AXPET fortreatmentverification (PS).

  3. „Evaluation of RPC-based PET appliedto in-beam HT monitoring“ – Review status. • Geometricaloptimizationforcrystal-based PET dedicatedto HT monitoring. • Novel PET design: AXPET fortreatmentverification

  4. PET for HT monitoring Nowadays, PET istheonlyfeasibleandclinicallyusedmethod. Challenges: • Crystal-based vs. Resistive-Plate-Chamber In-beam, in-room • Wash-out processes • Low positron yield • Partial ring geometry (*) • (*)only for in-beam Time Of Flight (TOF ) • Gas detector • Advantages: • Scintillating crystals and photon sensor. • Standard technology for clinical PET. • Excellent timing resolution • Inexpensive construction in large areas. • Depth of interacion information (layered structure) γ γ Scintillatingcrystal HV Position readout e- E Photodetectors

  5. RPC-based vs. Crystal-based PET for HT monitoring January 2012 April 2012 November 2012 November 2013 Deliverable 2.7: Comparisonofbothtechnologiesfortreatmentverification: performanceestimation (UGENT), individual hadron beam forrangeanalysis (IFIC) andtreatmentpatientdata (Dresden) After mid-termmeeting in Ciudad Real: UGENT proposedtopresentthisworkatthe IEEE-MIC conference in 2012  Oral Presentation. After November-2012 WP2 meeting: include in theworktheoptimizedgeometryofthe RPC-based PET Finalizingthepaper: twotechnologies, different geometries (full-ring and partial-ring; standardandextended), for a widerangeofsources

  6. Source Simulations -Performace evaluation sources (NEMA protocol) - Include a linear sourcesmallerthantheproposed in NEMA (70 cm to 15 cm) toadapttothetreatmentsizes presentedby S. Vanderberghe (UGENT) -Patient Treatment data from GSI - Presentedby H. Rohling (Oncoray, Un. Dresden) -Positron distribution hadron beam with Geant4 • Output: • Positron distributionproducedwithinthe PMMA phantom. Ideal hadron beam (noenergy, nopositionuncertainty) (L= 20 cm, D = 15 cm) Physicspackages: QGSP_BIC_HP forhadronic model andstandardforelectromagetic model

  7. Simulations of the detectors using GATE (Standard) RPC PET CRYSTAL-BASED PET (Gemini) Complete and 14-Heads RPC system Geometrycourtesyof F. Diblen, UGhent 28 Heads 80 cm 20 Heads • TOF FWHM: 50, 100, 200 ps 20/60 modules in a radial sector • Axial FOV: 30 cm • Diameter: 80 cm • Noenergyavailable • Crystal: 4x4x22 mm3,LYSO • TOF resolution: 200, 400, 600ps FWHM • Axial FOV: 18 cm • Diameter: 90 cm • Energywindow: 440-665 keV Stack composition 5 glass plates with 120x300x3.2 mm3 8 mm pitch 4 gas volumes filled with Freon • Spatial Resolution: σx = 3.9 mm (module); σy = 2 mm; σz = 4 mm • (Data providedbyD.Watts & F.Sauli)

  8. Simulations of the detectors using GATE (Extended & Optimized) OPTIMIZED RPC PET EXTENDED CRYSTAL-BASED PET (Gemini) 14-Heads RPC system GeometrycourtesyofD.Watts, Tera Geometrycourtesyof F. Diblen, UGhent • TOF FWHM: 50, 100, 200 ps 20 Heads • Axial FOV: 60 cm • Diameter: 80 cm • Noenergyavailable 80 cm • Crystal: 4x4x22 mm3,LYSO • TOF resolution: 200, 400,600 ps FWHM • Axial FOV: 40 cm • Diameter: 90 cm • Energywindow: 440-665 keV Stack composition 5 glass plates with 120x300x1.95 mm3 (glass thickness 150 μm) 4 mm pitch 4 gas volumes filled with Freon 60 modules in a radial sector Std Opt 8 mm 4 mm

  9. Image Reconstruction TOF-MLEM: Maximum-LikelihoodExpectation-Maximizationmodifiedtoinclude TOF information • Ray tracingbased on Siddonalgorithm • TOF: Gaussiandistributionwhose FWHM equaltothe time resolutionandmeanequaltotheexpectedpositionoftheemissionusingδT. Image Quality Evaluation R50: z coordinate where the distal part of the activity profile drops at 50% of the maximum. E98: z coordinate where the integral of the activity curve reaches 98% of the total area ROI: 20x20x200 mm centered on the beam 50% ofImax E98 R50

  10. Resultsforprotonbeams(I) Crystal-based (completeand partial ring system)

  11. Resultsforprotonbeams(II) Extended Crystal-based (completeand partial ring system)

  12. Resultsforprotonbeams(III) RPC-based, completesystem

  13. Resultsforprotonbeams(IV) RPC-based, partial ring

  14. Resultsforprotonbeams(V) Optimized RPC-based, partial ring Forcomparison: PR standardcrystal-based PR: 14; NMod: 60

  15. Resultsforprotonbeams (VI) R50 Crystal-based ΔRref(mm) E (MeV) Full Ring Partial Ring E (MeV) E (MeV) ΔRref(mm) RPC-based RPC-based

  16. Resultsforprotonbeams(VII) R50 Crystal-based, Std Crystal-based, Ext. ΔRref(mm) E (MeV) E (MeV) RPC-based, Std. ΔRref(mm) E (MeV) E (MeV) RPC-based, Opt.

  17. Conclusions • Limitingfactorfor RPC-based PET dedicatedto HT monitoringisthesensitivity (supportedbytheresultswithpatientdata). • Investigatingother geometries, such a trapezoidalmoduleswouldincreasethesensitivity(underinvestigation). • Althoughithasbeenshownthatthistechnologyhaslimitationsfor on-line monitoring, thisdoes not implythat RPC-baseddevicescould not beusefulforotherapplications (wholebodyimaging).

  18. „Evaluation of RPC-based PET appliedto in-beam HT monitoring“ – Review status. • Geometricaloptimizationforcrystal-based PET dedicatedto HT monitoring. • Novel PET design: AXPET fortreatmentverification

  19. Simulations of the hadron beam with Geant4.9.3 • Output: • Positron distributionproducedwithinthe PMMA phantom. (L= 20 cm, D = 15 cm) • G4 Physicspackages: • QGSP_BIC_HP forhadronicmodel • Standard forelectromagetic model Ideal hadron beam (noenergy, andpositionaluncertainty)

  20. Simulationsoftreatmentdatawith GATE andPosGen(*) Proton treatment (from WP6, courtesyofCh. Robert, IMNC - UMR 8165): Simulatedannihilationmapsbased on a treatmet plan using GATE-TPS sourceandthepatientreceived ~2 Gy per fractionwithtwobeams. Numberofsimulatedannihilationsis 3.5∙108 produced after 10 minutes. Carboniontreatment (from GSI, courtesyof H. Rohling, Oncoray): Simulatedannihilationmapsbased on a real treatmet plan of a clivalchondrosarcomaandthepatientreceived 0.662 Gy per fractionwithoneoftwofields. Numberofsimulatedannihilationsis 2.7∙106. (*) Poenisch, K. Parodi, B. G. Hasch, W. Enghardt: The modelling of positron emitter production and PET imaging during carbon ion therapy. Phys. Med. Biol. 49 5217-5232, 2004

  21. Simulations of the detectors using GATE 6.1 Dedicated PET: reduceddiameterandincreased axial extension improvedsensitivity Commercial PET: based on thegeometryofthe Philips Gemini (courtesyof F. Diblen, Un. Ghent) SPR-PET SC-PET PR-PET C-PET 30 cm 30 cm 40 cm 40 cm 60 cm 30 cm 60 cm 20 Heads 30 cm Sensitivityincrease

  22. Image Reconstruction TOF-MLEM: Maximum-LikelihoodExpectation-Maximizationmodifiedtoinclude TOF information • Ray tracingbased on Siddonalgorithm • TOF: Gaussiandistributionwhose FWHM equaltothe time resolutionandmeanequaltotheexpectedpositionoftheemissionusingδT. Image Quality Evaluation R50: z coordinate where the distal part of the activity profile drops at 50% of the maximum. ROI: 20x20x200 mm centered on the beam 50% ofImax R50

  23. Resultsforprotonbeams Comparisonstandard PET todedicated PET 160 MeVprotons, 40th iteration Full ring standard Partial ring standard PR-PET C-PET SPR-PET SC-PET Better TOF 200 400 600 Sentivityincrease Improvements in TOF removepartiallythewideningartifact due tothe partial ring, but theincrease in axial directionandthereductionofthedetectordiameterhave a higherimpact in reducingtheartifact.

  24. Range Verification Range calculationsfromthereconstructedpositrondistributionofprotonandcarbonionbeams Protons Carbon Ions

  25. Treatment datareconstruction Proton treatment: Annihilation Points Axial Coronal Sagittal SC-PET Profilesofthereconstructedimagesof SC-PET at different TOFs (15th iteration) TOF= 200 ps; 15th iteration Carboniontreatment: Annihilation Points C-PET SC-PET Nasal area: hotspotsfor C-PET andalmostnoactivityfor SC-PET, like in thereference

  26. Conclusions • Positron distributioncomingfromionbeams (protonsandcarbonions), itisobservedthatTOF haslittleeffect on therangecalculations. The sensitivityofthescanneriscrucialtoachieve 3-mm rangedifference. Betterimagesofthepositrondistributionof a real treatment plan are also observedforthehighest sensitive PET configuration. In theshortterm, quantitative analysisofpatientdatawithprotonsandcarbonions will beincluded in ourstudytocharacterizetheminimumrequirements in termsofsensitivityof a PET systemfor on-line dose monitoring.

  27. „Evaluation of RPC-based PET appliedto in-beam HT monitoring“ – Review status. • Geometricaloptimizationforcrystal-based PET dedicatedto HT monitoring. • Novel PET design: AXPET fortreatmentverification (P. Solevi)

  28. AX-PET: 100 mm long LYSO crystals, axially oriented with 3x3 mm2 section, combined with an array of WLS strips. Both LYSO and WLS are individually read-out by SiPMs. AX-PET concept & features • Sensitivity and resolution decoupled • Reduced parallax error WLS • Full ring based on AX-PET is tested for in-room PET. Why? LYSO Large fraction of triple events yielded can increase sensitivity, crucial for HT monitoring. A modified AX-PET module was tested with dSiPM and provides 269 ps CRT (FWHM). ”A Monte-Carlo based model of the AX-PET demonstrator and its experimental validation” P. Solevi et al, PMB 58 (2013)

  29. First results in HT monitoring Pencil p and C ions monoenergetic beams: triple inclusion study. C ion treatment in PMMA, 5 minutes long acquisition, 2 Gy delivered, TOF study. Double+triples, 5' long acq. Double, 5' long acq.

  30. Thanksforyourattention!!! • Acknowlegments: • ENVISION projectco-fundedbythe European Commissionunderthe FP7 grantagreementno. 241851. • ITN ENTERVISION (FP7, G.A. No. 264552). • Spanish Ministerio de Economía y Hacienda, through “Juan de la Ciervaprogram“, FPA2010-14891 grant, FIS2011-14585, and PTA2011-6139-I. • GeneralitatValencianathrough GV/2013/133. • University of Valencia trough UV-INV-PRECOMP12-80755.

  31. ENVISION Project • European NoVelImaging Systems forIONtherapy • on-line dose monitoringbydevelopingnovelimagingmodalitiesrelatedto dose depositionthatallowtoassessthetreatedvolumeduringhadrontherapy Hadron beam TOF γ Patient γ Tumor TOF in-beam PET (crystal- and RPC-based) to reconstruct the positron distribution generated by the hadron beam γ Scintillators crystals (LaBr3) to build a Compton Camera to image the „prompt gamma“ generated in the first nanoseconds.

  32. WPs in ENVISION • IRIS groupisinvolved in: • WP2: TOF in-beam PET (crystal- and RPC-based). • WP3: detectionof prompt radiation (in-beam SPAT: gamma, lightchargedparticlesandneutrons), overcomingtheinherentsensitivityofib-PET tometabolism.

  33. PET and Compton Camerafor HT monitoring Novelmethodof in-vivo dosimetrybased on thedetectionoftheprompt-gammaproduced after thetherapeutic beam  not affectedbythewash-out processes Nowadays, PETistheonlyfeasibleandclinicallyusedmethod. Challenges: • Wash-out processes • Low positronyield, short half-lifepositronemitters • Partial ring geometry(*) • (*)onlyfor in-beam In-beam, in-room Time Of Flight (TOF ) Detectiontechnique: Compton Camera

  34. TOF RPC-based PET • RPC stands for Resistive Plate Chamber • Gas detector • Advantages: • Excellent timing resolution • Inexpensive construction in large areas. • Depth of interacion information (layered structure) • Basics: • Incoming photon ionizes the gas • High voltage creates an avalanche of electrons • Several layers gives good detection efficiency • Thin layers gives better timing properties Sensitive Area (precisesmallgap 300 μm) (M. Couceiro, Jornadas DFM, 2010)

  35. Results for carbon beams (I) CRYSTAL-PET RPC-PET

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