High Performance Optical Computed Tomography for Accurate Three-Dimensional Radiation

256 Pages·2017·25.54 MB·English

WWeesstteerrnn UUnniivveerrssiittyy
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Electronic Thesis and Dissertation Repository
3-28-2018 2:00 PM
HHiigghh PPeerrffoorrmmaannccee OOppttiiccaall CCoommppuutteedd TToommooggrraapphhyy ffoorr AAccccuurraattee
TThhrreeee--DDiimmeennssiioonnaall RRaaddiiaattiioonn DDoossiimmeettrryy
Kurtis Hendrik Dekker, The University of Western Ontario
Supervisor: Jordan, Kevin J., The University of Western Ontario
Joint Supervisor: Battista, Jerry J., The University of Western Ontario
A thesis submitted in partial fulfillment of the requirements for the Doctor of Philosophy degree
in Medical Biophysics
© Kurtis Hendrik Dekker 2018
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Part of the Medical Biophysics Commons
RReeccoommmmeennddeedd CCiittaattiioonn
Dekker, Kurtis Hendrik, "High Performance Optical Computed Tomography for Accurate Three-
Dimensional Radiation Dosimetry" (2018). Electronic Thesis and Dissertation Repository. 5264.
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Abstract
Optical computed tomography (CT) imaging of radiochromic gel dosimeters is a method
for truly three-dimensional radiation dosimetry. Although optical CT dosimetry is not
widely used currently due to previous concerns with speed and accuracy, the complexity
of modern radiotherapy is increasing the need for a true 3D dosimeter. This thesis reports
technicalimprovementsthatbringtheperformanceofopticalCTtoaclinicallyusefullevel.
Newscannerdesignsandimprovedscanningandreconstructiontechniquesaredescribed.
First,wedesignedandimplementedanewlightsourceforacone-beamopticalCTsystem
whichreducedthescattertoprimarycontributioninCTprojectionimagesofgeldosimeters
fromapproximately25%toapproximately4%. Thisdesign,whichhasbeencommercially
implemented,enablesaccurateandfastdosimetry.
Second, we designed and constructed a new, single-ray, single-detector parallel-beam op-
tical CT scanner. This system was able to very accurately image both absorbing and scat-
tering objects in large volumes (15 cm diameter), agreeing within ∼1% with independent
measurements. IthasbecomeareferencestandardforevaluationofopticalCTgeometries
anddosimeterformulations.
Third, we implemented and characterized an iterative reconstruction algorithm for optical
CT imaging of gel dosimeters. This improved image quality in optical CT by suppressing
theeffectsofnoiseandartifactsbyafactorofupto5.
Fourth, we applied a fiducial-based ray path measurement scheme, combined with an iter-
ativereconstructionalgorithm,toenableopticalCTreconstructioninthecaseofrefractive
index mismatch between different media in the scanner’s imaged volume. This improved
thepracticalityofopticalCT,astime-consumingmixingofliquidscanbeavoided.
Finally,weappliedthenewlaserscannertothedifficultdosimetrytaskofsmall-fieldmea-
surement. We were able to obtain beam profiles and depth dose curves for 4 fields (≤ 3×3
ii
cm2) using one 15 cm diameter dosimeter, within 2 hours. Our gel dosimetry depth-dose
curvesagreedwithin∼1.5%withMonteCarlosimulations.
In conclusion, the developments reported here have brought optical CT dosimetry to a
clinicallyusefullevel. Ourtechniqueswillbeusedtoassistfutureresearchingeldosimetry
andradiotherapytreatmenttechniques.
Keywords: Cancer, Radiation Therapy, Radiation Dosimetry, Small-field Dosimetry,
ComputedTomography,OpticalImaging,StrayLight,LaserScanning
iii
Co-Authorship Statement
Chapter 2 is adapted from a manuscript published as “Stray light in cone beam optical
computedtomography: II.Reductionusingaconvergentlightsource”byKurtisH.Dekker,
Jerry J. Battista and Kevin J. Jordan, Physics in Medicine and Biology, 61, 2910-2925
(2016). KHD designed the study, performed experiments and analysis, and wrote and
editedthemanuscript. KJJandJ2Bsupervised,providedinputonstudydesignandanalysis,
andeditedthemanuscript.
Chapter 3 is adapted from a manuscript published as “Scanning laser optical computed to-
mographysystemforlargevolume3Ddosimetry”byKurtisH.Dekker,JerryJ.Battistaand
Kevin J. Jordan, Physics in Medicine and Biology, 62, 2636-2657 (2017). KHD designed
the study, performed experiments and analysis, and wrote and edited the manuscript. KJJ
andJ2Bsupervised,providedinputonstudydesignandanalysis,andeditedthemanuscript.
Chapter 4 is adapted from a manuscript published as “Technical Note: Evaluation of an
iterativereconstructionalgorithmforopticalCTradiationdosimetry”byKurtisH.Dekker,
Jerry J. Battista and Kevin J. Jordan, Medical Physics, 44, 6678-6689. KHD designed the
study, performed experiments and analysis, and wrote and edited the manuscript. KJJ and
J2Bsupervised,providedinputonstudydesignandanalysis,andeditedthemanuscript.
Chapter 5 is adapted from a manuscript published as “Optical CT imaging of solid ra-
diochromicdosimetersinmismatchedrefractiveindexsolutionsusingascanninglaserand
large area detector” by Kurtis H. Dekker, Jerry J. Battista and Kevin J. Jordan, Medical
Physics,43,4585-4597(2016). KHDdesignedthestudy,performedexperimentsandanal-
ysis,andwroteandeditedthemanuscript. KJJandJ2Bsupervised,providedinputonstudy
designandanalysis,andeditedthemanuscript.
Chapter 6 describes gel dosimetry experiments performed at the London Regional Cancer
Program. Experiments were performed by Kurtis H. Dekker, Sydney Bell, and Kevin J.
iv
Jordan. KHD performed optical CT imaging and analysis, assisted in irradiations, and
authored the chapter. SB manufactured gel dosimeters and performed irradiations. KJJ
supervised experiments, manufactured gel dosimeters, performed irradiations and edited
thechapter. JerryJ.Battistaalsoeditedthechaptermanuscript.
Appendix A is adapted from a technical note published as “Fixed, object-specific intensity
compensation for cone beam optical CT radiation dosimetry” by Kurtis Hendrik Dekker,
Rubin Hazarika, Matheus A. Silveira, and Kevin J. Jordan, Physics in Medicine and Biol-
ogy,63, 06NT02(2018). KHDdesignedthestudy, supervisedandperformedexperiments,
and wrote and edited the manuscript. RH and MAS performed experiments and edited the
manuscript. KJJprovidedinputonstudydesign,supervised,andeditedthemanuscript.
v
Acknowledgements
First, I would like to thank my supervisors, Drs. Kevin Jordan and Jerry Battista, whose
guidance and passion for medical physics enabled and inspired my development as a re-
searcher. I also wish to thank my advisory committee members, Drs. Tim Scholl and
GeorgeHajdok,forvolunteeringtheirtimeandinsightsinmy(veryinfrequent)committee
meetings. I am also grateful to the examiners for volunteering their time to review this
dissertation.
IwishtothankthestaffintheDepartmentofMedicalBiophysicsofficefortheirhelpwith
various administrative details. I would also like to extend my gratitude to the Department
of Physics and Engineering at the London Regional Cancer Program. In particular: Barb
Barons, for administrative support; George De Waele, for machining various components;
the engineering group, for help with the linear accelerators; and the physicists and physics
associates,fortheirguidanceandknowledgeofclinicalradiotherapyphysics. Additionally,
Ithanktheco-opstudentsIhaveworkedwithoverthepastfiveyears.
I would also like to acknowledge the sources of funding that contributed to my disser-
tation, including the London Regional Cancer Program and the Department of Medical
Biophysics at the University of Western Ontario. In addition, funding for the project was
providedbytheOntarioResearchChallengeFund(OCAIROproject)andagrantfromthe
Plunkett foundation in London, Ontario. My graduate studies have also been supported by
scholarships from the Ontario Ministry of Training, Colleges, and Universities and from
theNaturalSciencesandEngineeringResearchCouncilofCanada(NSERC).
I thank all of my friends, both in the department here and outside of it. Finally, I thank my
brother,Lukas;myparents,RonandTeresa;andmyfiancée,Erin,fortheirsupport.
vi
Contents
Abstract ii
Co-AuthorshipStatement iv
Acknowlegements vi
TableofContents vii
ListofFigures xiii
ListofTables xx
ListofAppendices xxii
ListofAbbreviations xxiii
ListofSymbols xxv
1 GeneralIntroduction 1
1.1 CancerBasics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 CancerinCanada . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 RadiationTherapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Radiationtherapyprocess . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.2 Advancesinexternalbeamradiotherapy . . . . . . . . . . . . . . . 6
1.3 RadiotherapyQualityAssurance . . . . . . . . . . . . . . . . . . . . . . . 9
1.4 RadiationDosimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.4.1 Propertiesofdosimeters . . . . . . . . . . . . . . . . . . . . . . . 10
1.4.2 Comparisonofcommondosimeters . . . . . . . . . . . . . . . . . 13
1.5 TheCasefor3DDosimeters . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.6 3DChemicalDosimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.6.1 Geldosimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.6.1.1 Geldosimeterbasics . . . . . . . . . . . . . . . . . . . . 17
1.6.1.2 Condensedhistoryofgeldosimetry . . . . . . . . . . . . 18
1.6.2 Non-gel3Dchemicaldosimeters . . . . . . . . . . . . . . . . . . . 19
1.6.3 3Dchemicaldosimeterreadout . . . . . . . . . . . . . . . . . . . . 20
1.7 OpticalComputedTomography . . . . . . . . . . . . . . . . . . . . . . . . 21
1.7.1 Computedtomographybasics . . . . . . . . . . . . . . . . . . . . 21
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1.7.1.1 Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.7.1.2 Projections . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.7.1.3 TheFourierSliceTheoremandtomographicreconstruction 24
1.7.1.4 Backprojection-basedreconstructiontechniques . . . . . 26
1.7.1.5 Algebraic/Iterativereconstructionalgorithms . . . . . . 27
1.7.2 OpticalCTscanners . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.8 MotivationofResearch . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.8.1 Straylighteffects . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.8.1.1 Straylightinattenuationmeasurements . . . . . . . . . . 31
1.8.1.2 StraylightinopticalCT . . . . . . . . . . . . . . . . . . 32
1.8.1.3 StraylightreductioninopticalCT . . . . . . . . . . . . . 35
1.8.2 Largevolumedosimetry . . . . . . . . . . . . . . . . . . . . . . . 35
1.8.3 Opticalartifactsandimagereconstruction . . . . . . . . . . . . . . 36
1.9 ResearchHypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.10 SpecificObjectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
1.11 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2 StrayLightReductioninCone-beamOpticalCT 46
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.2 MaterialsandMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.2.1 FresnelmodifiedopticalCTscanner . . . . . . . . . . . . . . . . . 48
2.2.2 Verticalslotarray . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.2.3 Testsolutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.2.4 Phantoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.2.4.1 UniformsolutioninVista10vessel . . . . . . . . . . . . 53
2.2.4.2 FEPfingerphantom . . . . . . . . . . . . . . . . . . . . 56
2.2.5 Experimentalsetups . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.2.5.1 Fanbeamvs. narrowbeamgeometry . . . . . . . . . . . 57
2.2.5.2 Fanbeamvs. conebeam-uniformphantom . . . . . . . 58
2.2.5.3 Fanbeamvs. conebeam-fingerphantom . . . . . . . . . 58
2.2.5.4 Gelatinfingerphantomimaging . . . . . . . . . . . . . . 58
2.2.5.5 Sourcespotsizeoptimization . . . . . . . . . . . . . . . 59
2.3 ResultsandDiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.3.1 Straylight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.3.1.1 Fanbeamvs. narrowbeamgeometry . . . . . . . . . . . 60
2.3.1.2 Uniformphantom . . . . . . . . . . . . . . . . . . . . . 61
2.3.1.3 Fanbeamvs. conebeam-fingerphantom . . . . . . . . . 62
2.3.1.4 Gelatinfingerphantom . . . . . . . . . . . . . . . . . . . 63
2.3.2 Imageartifactsandsourcespotsizeoptimization . . . . . . . . . . 65
2.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
2.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3 Large-volumeScanningLaserOpticalCT 72
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.1.1 OpticalCTdosimetry . . . . . . . . . . . . . . . . . . . . . . . . . 72
viii
3.1.2 Large-volume3Ddosimetry . . . . . . . . . . . . . . . . . . . . . 73
3.1.3 OpticalCTscanners . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.1.4 StraylighteffectsinopticalCT . . . . . . . . . . . . . . . . . . . . 74
3.1.5 Studyobjectivesandoutline . . . . . . . . . . . . . . . . . . . . . 75
3.2 ScannerDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.2.1 Choiceofscannergeometry . . . . . . . . . . . . . . . . . . . . . 78
3.2.2 OpticalCTaquarium . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.2.2.1 Lens-shapedacylindricalaquarium . . . . . . . . . . . . 79
3.2.2.2 Importanceofasymmetricdesign . . . . . . . . . . . . . 80
3.2.3 Detectorcollimationandflood-fielduniformity . . . . . . . . . . . 80
3.2.4 CTsamplingandreconstruction . . . . . . . . . . . . . . . . . . . 81
3.3 InitialCharacterizationTests . . . . . . . . . . . . . . . . . . . . . . . . . 83
3.3.1 Detectorlinearity . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3.3.2 Noiseandstability . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.3.3 Parallelbeamgeometryverification . . . . . . . . . . . . . . . . . 85
3.3.4 Spatialresolutioninprojectionimages . . . . . . . . . . . . . . . . 86
3.3.5 Summaryofspecifications . . . . . . . . . . . . . . . . . . . . . . 87
3.4 OpticalCTscanningexperiments . . . . . . . . . . . . . . . . . . . . . . . 88
3.4.1 Phantoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.4.2 OpticalCTscanparameters . . . . . . . . . . . . . . . . . . . . . . 88
3.4.3 Large-volumeuniformabsorbingphantom . . . . . . . . . . . . . . 89
3.4.4 Large-volumeuniformscatteringphantom . . . . . . . . . . . . . . 90
3.4.5 Smallabsorbingfingerphantomingel-likescatteringmedium . . . 90
3.4.6 Small absorbing finger phantom in highly scattering medium - op-
posingsinogramreconstructions . . . . . . . . . . . . . . . . . . . 91
3.5 ResultsandDiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.5.1 Large-volumeuniformabsorbingphantom . . . . . . . . . . . . . . 93
3.5.2 Large-volumescatteringphantom . . . . . . . . . . . . . . . . . . 95
3.5.3 Absorbingfingerphantomingel-likescatteringmedium . . . . . . 97
3.5.4 Small absorber in highly scattering medium - opposing sinogram
reconstructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
3.5.5 Summaryofresultsandcurrentlimitations . . . . . . . . . . . . . . 101
3.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
3.7 Appendix: RayTracingforAquariumDesign . . . . . . . . . . . . . . . . 103
3.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4 IterativeReconstructioninOpticalCT:NoiseandArtifactReduction 108
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
4.1.1 OpticalCTdosimetry . . . . . . . . . . . . . . . . . . . . . . . . . 108
4.1.2 Effectsofimagenoiseandartifactsondosimetricanalysis . . . . . 109
4.1.3 IterativeCTreconstruction . . . . . . . . . . . . . . . . . . . . . . 111
4.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.2.1 OpticalCTscanner . . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.2.2 OpticalCTdatasets . . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.2.2.1 Phantomdatasets . . . . . . . . . . . . . . . . . . . . . . 113
ix
4.2.2.2 Geldataset . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.2.3 Imagereconstruction . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.2.3.1 Filteredbackprojection(FBP) . . . . . . . . . . . . . . . 114
4.2.3.2 Ordered subsets convex algorithm with total variation
minimization(OSC-TV) . . . . . . . . . . . . . . . . . . 115
4.2.4 Imagereconstructiondetails . . . . . . . . . . . . . . . . . . . . . 117
4.2.4.1 OSC-TViterationstoppingconditions . . . . . . . . . . . 118
4.2.5 Imageanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
4.2.5.1 Meanandstandarddeviation . . . . . . . . . . . . . . . . 119
4.2.5.2 Contrasttoartifact+noiseratio(CANR) . . . . . . . . . 119
4.2.5.3 GradientPreservation . . . . . . . . . . . . . . . . . . . 119
4.3 ResultsandDiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
4.3.1 Uniformsolutionphantom(PhantomA) . . . . . . . . . . . . . . . 120
4.3.2 FingerPhantom(PhantomB) . . . . . . . . . . . . . . . . . . . . . 123
4.3.2.1 Contrasttoartifact+noiseratio . . . . . . . . . . . . . . 123
4.3.2.2 Gradientsharpness . . . . . . . . . . . . . . . . . . . . . 123
4.3.3 Geldosimeterwithsmallfields(PhantomC) . . . . . . . . . . . . . 125
4.3.3.1 Contrasttoartifact+noiseratio . . . . . . . . . . . . . . 125
4.3.3.2 Gradientsharpness . . . . . . . . . . . . . . . . . . . . . 126
4.3.3.3 Fieldcentralattenuationcoefficientvalue . . . . . . . . . 128
4.3.4 Investigationofmeancentralvaluedrop-off . . . . . . . . . . . . . 129
4.4 DiscussionandConclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 130
4.5 Appendix: CalculationofTotalVariationGradient . . . . . . . . . . . . . . 132
4.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
5 IterativeReconstructioninOpticalCT:MismatchedRefractiveIndexScan-
ning 137
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.1.1 Opticalcomputedtomography(CT)forthree-dimensional(3D)ra-
diationdosimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.1.2 PRESAGE(cid:13)R soliddosimeters . . . . . . . . . . . . . . . . . . . . . 138
5.1.3 Intentionallymismatchedrefractiveindex . . . . . . . . . . . . . . 140
5.1.4 Studyoutline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
5.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
5.2.1 ScanninglaseropticalCTsystem . . . . . . . . . . . . . . . . . . . 142
5.2.1.1 Scanningwavelengths . . . . . . . . . . . . . . . . . . . 144
5.2.2 Raypathmeasurement . . . . . . . . . . . . . . . . . . . . . . . . 144
5.2.2.1 Mathematicaldescription . . . . . . . . . . . . . . . . . 144
5.2.2.2 Implementation in optical CT iterative reconstruction
process . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
5.2.3 Aquariumliquidselection . . . . . . . . . . . . . . . . . . . . . . 147
5.2.4 CTscanningandreconstruction . . . . . . . . . . . . . . . . . . . 148
5.2.5 Validationoftechniquewithauniformsolutionphantom . . . . . . 149
5.2.6 PRESAGE(cid:13)R experiments . . . . . . . . . . . . . . . . . . . . . . . 150
5.2.6.1 Irradiationsetup . . . . . . . . . . . . . . . . . . . . . . 150
x