Scintillation dosimetry: Scintillation dosimetry: Review, new innovations and Review, new innovations and applications applications Sam Beddar, Ph.D., Sam Beddar, Ph.D., Professor Professor Department of Radiation Physics, UT MD Anderson Cancer Center Department of Radiation Physics, UT MD Anderson Cancer Center & UT Graduate School of Biomedical Sciences & UT Graduate School of Biomedical Sciences & Luc Beaulieu, Ph.D., Luc Beaulieu, Ph.D., Associate Professor Associate Professor Department of Physics, Department of Physics, Universit Université Laval & Laval & Department of Radiation Department of Radiation Oncology, CHU de Quebec Oncology, CHU de Quebec OUTLINE UTLINE • Introduction Introduction • Properties of plastic Properties of plastic scintillation detectors scintillation detectors • Applications Applications – Daily QA Daily QA – Radiosurgery Radiosurgery – Clinical prototype Clinical prototype – Proton therapy Proton therapy – Works in progress Works in progress • Conclusions Conclusions
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Scintillation dosimetry: Review, new innovations and ... · Scintillators with longer wavelengths have lower light emission Archambault L, Arsenault J, Gingras L, Beddar A S, Roy
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Scintillation dosimetry: Scintillation dosimetry: Review, new innovations and Review, new innovations and
applicationsapplications
Sam Beddar, Ph.D., Sam Beddar, Ph.D., ProfessorProfessor
Department of Radiation Physics, UT MD Anderson Cancer Center Department of Radiation Physics, UT MD Anderson Cancer Center & UT Graduate School of Biomedical Sciences& UT Graduate School of Biomedical Sciences
&&
Luc Beaulieu, Ph.D., Luc Beaulieu, Ph.D., Associate Professor Associate Professor
Department of Physics, Department of Physics, UniversitUniversitéé Laval & Laval & Department of Radiation Department of Radiation Oncology, CHU de QuebecOncology, CHU de Quebec
OOUTLINEUTLINE
•• IntroductionIntroduction
•• Properties of plastic Properties of plastic scintillation detectorsscintillation detectors
•• ApplicationsApplications–– Daily QADaily QA–– RadiosurgeryRadiosurgery–– Clinical prototypeClinical prototype–– Proton therapyProton therapy–– Works in progressWorks in progress
•• In the last 20 years, significant advances have been made In the last 20 years, significant advances have been made in scintillation dosimetryin scintillation dosimetry
•• They have a unique set of advantagesThey have a unique set of advantages
•• With the increasing complexity of radiotherapy treatments, With the increasing complexity of radiotherapy treatments, scintillation detectors could be used for quick and accurate scintillation detectors could be used for quick and accurate dose measurements even in complex geometriesdose measurements even in complex geometries
The purpose of this presentation is to show the advantages The purpose of this presentation is to show the advantages of of scintillatonscintillaton dosimetry and to explain how it can be used dosimetry and to explain how it can be used in modern radiotherapyin modern radiotherapy
•• In scintillation detectors:In scintillation detectors:
•• Impinging particles or photons will excite atoms or Impinging particles or photons will excite atoms or molecules of the scintillating medium.molecules of the scintillating medium.
•• Electron beams: Interacting electrons are not the same as Electron beams: Interacting electrons are not the same as the ionization electronsthe ionization electrons
•• The decay of these excited states will produce The decay of these excited states will produce photons in the visible part of the spectrum.photons in the visible part of the spectrum.
•• Photon beams: Interacting photons are not the same as the Photon beams: Interacting photons are not the same as the detected photonsdetected photons
•• These photons will be guided to a These photons will be guided to a photodetectorphotodetector and and then converted in an electric signal.then converted in an electric signal.
-- Lower density Lower density …… and!!! nearly equivalent to waterand!!! nearly equivalent to water•• Density on the order of 1.03Density on the order of 1.03--1.06 g/cm1.06 g/cm33
•• (Generally) No high Z materials content.(Generally) No high Z materials content.
-- Excitation and emission spectra are similar in Excitation and emission spectra are similar in solid, liquid or vapor statessolid, liquid or vapor states
• Only a small portion of the incident kinetic energy lost is converted in fluorescent energy
– For plastic scintillating fibers like BCF-12 about 8000 photons/MeV
This means about 125 eV / scintillation photon.The total energy of visible light produced (at 430 nm or ~ 2.9 eV) represents an efficiency of 2.4% (97.6% goes in phonons!)
– The light output depends on the LET (i.e. CP type)
• The relationship between the specific energy loss (ionization density) and the light output is given by the Birks’ formula:
S: Scintillation efficiencyB(dE/dx): Density of damaged
molecules along the particle trackk: fraction of damage contributing to
quenching
– For electrons above 125 keV: dL/dx = S dE/dx» Thus L = SE !
– For large dE/dx, saturation can occurs along the track» dL/dx = S / (kB) (usualy for ion particles)
BIRKS’ FORMULA • Introduction• Properties• Applications• Conclusion
dLdx
=S dEdx
1+ kB dEdx
Archambault L, Beddar S, Sahoo N, Archambault L, Beddar S, Sahoo N, PoensichPoensich F, Gillin M, Mohan R, " Experimental Proof and F, Gillin M, Mohan R, " Experimental Proof and Feasibility of a 3D RealFeasibility of a 3D Real--Time Detector System for Therapeutic Proton Beams Time Detector System for Therapeutic Proton Beams ““, Med. Phys. 35: , Med. Phys. 35: 2905, 2008. (Abstract).2905, 2008. (Abstract).
• Organic (plastic) scintillators are:– Made of low Z materials.
– Light output is directly proportional to the exciting energy.» Linear with deposited energy for e-,γ.» …for electron above 100-125 keV.
– (Mostly) Transparent to its emitted photons.
– The gap is wide enough to be insensitive to a wide range of temperatures.
– Fast time response (physics of orbital transitions).
Beddar A S, Mackie T R, Beddar A S, Mackie T R, AttixAttix F H, "WaterF H, "Water--equivalent plastic scintillation detectors for highequivalent plastic scintillation detectors for high--energy beam dosimetry: I. energy beam dosimetry: I. Physical characteristics and theoretical considerationsPhysical characteristics and theoretical considerations““, Phys. Med. Biol. 37: 1883, Phys. Med. Biol. 37: 1883--1900, 1992. 1900, 1992.
Plastic scintillating fibers offer a good alternative to regular plastic scintillators:
• Increased light capture due to cladding (>internal reflection) • The cladding is also water-equivalent/ no perturbation
ORIGINAL PROTOTYPE
• High sensitivity (PMT)• Remove Cerenkov with background subtraction
Beddar, A S, Mackie, T R, and Attix, F H, "WaterBeddar, A S, Mackie, T R, and Attix, F H, "Water--equivalent plastic scintillation detectors for highequivalent plastic scintillation detectors for high--energy energy beam dosimetry: I. Physical characteristics and theoretical consbeam dosimetry: I. Physical characteristics and theoretical considerations," Phys. Med. Biol. 37: 1883iderations," Phys. Med. Biol. 37: 1883--1900, 1992. 1900, 1992.
Beddar A S, Mackie T R, Beddar A S, Mackie T R, AttixAttix F H, "WaterF H, "Water--equivalent plastic scintillation detectors for highequivalent plastic scintillation detectors for high--energy beam dosimetry: I. energy beam dosimetry: I. Physical characteristics and theoretical considerationsPhysical characteristics and theoretical considerations““, Phys. Med. Biol. 37: 1883, Phys. Med. Biol. 37: 1883--1900, 1992. 1900, 1992.
Although the light spectrum due to Cerenkov emission is differenAlthough the light spectrum due to Cerenkov emission is different t from the scintillation spectrum, de Boer et al have shown that sfrom the scintillation spectrum, de Boer et al have shown that spectral pectral filtration is not sufficient to remove completely the Cerenkov lfiltration is not sufficient to remove completely the Cerenkov light.ight.
• In plastics like polystyrene, electrons with energies 146 keV and higher produce a blue light due to Cerenkov emission
• This light is superposed on the scintillation signal• If a large amount of clear optical fiber is in the radiation
field, Cerenkov emission can be significant (>15 %)
de Boer S F, Beddar A S Rawlinson J F "Optical filtering and spde Boer S F, Beddar A S Rawlinson J F "Optical filtering and spectral measurement of radiationectral measurement of radiation--induced light in plastic scintillator dosimetryinduced light in plastic scintillator dosimetry““, Phys Med , Phys Med BiolBiol 38: 94538: 945--958, 1993. 958, 1993.
• Commercialized product• Rugged and simple to construct• Good stability and reproducibility• Independent of temperature and pressure• No high-voltage bias• Remote operation and reset• Easily used by trained technical staff• Cost effective
Beddar S, Beddar S, ““A new scintillator detector system for the quality assurance of A new scintillator detector system for the quality assurance of 6060Co and highCo and high--energy therapy energy therapy machinesmachines””. Phys Med . Phys Med BiolBiol 39: 25339: 253––263, 1994. 263, 1994.
A DAILY QA DETECTOR SYSTEM • Introduction• Properties• Applications• Conclusion
Stability of the QA device over time
Beddar A S, Beddar A S, ““A new scintillator detector system for the quality assurance of A new scintillator detector system for the quality assurance of 60Co and high60Co and high--energy energy therapy machinestherapy machines””, Phys Med , Phys Med BiolBiol 39: 25339: 253––263, 1994. 263, 1994.
A DAILY QA DETECTOR SYSTEM • Introduction• Properties• Applications• Conclusion
SCINTILLATION FIBER ARRAYPROTOTYPE
• Alta U2000c• Interline• Color• Cooled @ -20º
• Fixed focal• f/# = 1.4
• PMMA
• BCF12 (blue)
• Subtract Cerenkov contamination with chromatic removalArchambault L, Beddar S, Archambault L, Beddar S, GingrasGingras L, Roy R, Beaulieu L, "Measurement accuracy and Cerenkov L, Roy R, Beaulieu L, "Measurement accuracy and Cerenkov removal for high performance, high spatial resolution scintillatremoval for high performance, high spatial resolution scintillation dosimetryion dosimetry““, Med. Phys. 33: 128, Med. Phys. 33: 128--135, 135, 2006. 2006.
LacroixLacroix F, Archambault L, F, Archambault L, GingrasGingras L, Beddar AS, and Beaulieu L. Clinical prototype of a plastic wL, Beddar AS, and Beaulieu L. Clinical prototype of a plastic waterater--equivalent scintillating fiber dosimeter matrix for IMRT QA applequivalent scintillating fiber dosimeter matrix for IMRT QA applications, Med Phys 35 (2008) 3682ications, Med Phys 35 (2008) 3682--3690.3690.
LacroixLacroix F, Archambault L, F, Archambault L, GingrasGingras L, Beddar AS, and Beaulieu L. Clinical prototype of a plastic wL, Beddar AS, and Beaulieu L. Clinical prototype of a plastic waterater--equivalent scintillating fiber dosimeter matrix for IMRT QA applequivalent scintillating fiber dosimeter matrix for IMRT QA applications, Med Phys 35 (2008) 3682ications, Med Phys 35 (2008) 3682--3690.3690.
LacroixLacroix F, Archambault L, F, Archambault L, GingrasGingras L, Beddar AS, and Beaulieu L. Clinical prototype of a plastic wL, Beddar AS, and Beaulieu L. Clinical prototype of a plastic waterater--equivalent scintillating fiber dosimeter matrix for IMRT QA applequivalent scintillating fiber dosimeter matrix for IMRT QA applications, Med Phys 35 (2008) 3682ications, Med Phys 35 (2008) 3682--3690.3690.
Beddar, A. S., Mackie, T. R., and Attix, F. H., "WaterBeddar, A. S., Mackie, T. R., and Attix, F. H., "Water--equivalent plastic scintillation detectors for highequivalent plastic scintillation detectors for high--energy beam dosimetry: II. Properties and measurements," Phys. Menergy beam dosimetry: II. Properties and measurements," Phys. Med. Biol. 37, 1901ed. Biol. 37, 1901--1913 (1992) c1913 (1992) c
Beddar, A. S., Mackie, T. R., and Attix, F. H., "WaterBeddar, A. S., Mackie, T. R., and Attix, F. H., "Water--equivalent plastic scintillation detectors for highequivalent plastic scintillation detectors for high--energy beam dosimetry: II. Properties and measurements," Phys. Menergy beam dosimetry: II. Properties and measurements," Phys. Med. Biol. 37, 1901ed. Biol. 37, 1901--1913 (1992) c1913 (1992) c
Beddar S, Beddar S, KinsellaKinsella T J, T J, IkhlefIkhlef A, Sibata C H, A, Sibata C H, ““Miniature 'ScintillatorMiniature 'Scintillator--FiberopticFiberoptic--PMT' detector PMT' detector system for the dosimetry of small fields in stereotactic system for the dosimetry of small fields in stereotactic radiosurgeryradiosurgery””, IEEE Trans. Nucl. Sci. 48: , IEEE Trans. Nucl. Sci. 48: 924924--928, 2001.928, 2001.
MONTE CARLO SIMULATIONS FOR PROTON BEAMS• Use Geant4 for a complete simulation
– Electromagnetic and hadronic processes– Production and tracking of visible light (scintillation and
Cerenkov)• Understand the behavior of a plastic scintillator
irradiated with protons• Optimize light collection efficiency
• Rapid, but requires correction for light propagation• Similar to a-Si dosimetry, but takes advantage of the
water equivalence of the plastic scintillator• Not as accurate as point-like scintillation dosimeters• See Petric et al. for more information
PetricPetric M P, M P, RobarRobar J L, Clark B G, J L, Clark B G, ““Development Development and characterization of a tissue equivalent plastic and characterization of a tissue equivalent plastic scintillator based dosimetry system,scintillator based dosimetry system,”” Med Phys 33: Med Phys 33: 9696--105, 2006.105, 2006.
• Scintillator irradiated with low energy (< 125 keV) photons is less water equivalent than megavoltage photons
• Chemical composition of plastic scintillator may be changed for a better response (Williamson et al., Kirov et al.)
• Kirov et al. have developed a 3D scintillation detector for the characterization of Ru-106 eye plaques
Kirov A S, Kirov A S, PiaoPiao J Z, J Z, MathurMathur N K, Miller T R, N K, Miller T R, DevicDevic S, S, trichtertrichter S, S, ZaiderZaider M, M, SoaresSoares C G, C G, LoSassoLoSasso T, T, ““ThreeThree--dimensional scintillation dimensional scintillation dosimetry method: test for a 106Ru plaque dosimetry method: test for a 106Ru plaque applicatorapplicator””, Phys Med , Phys Med BiolBiol 50: 306350: 3063--3081, 3081, 2005.2005.
see also Williamson J F, Dempsey J F, Kirov A S, Monroe J I, see also Williamson J F, Dempsey J F, Kirov A S, Monroe J I, BinnsBinns W R, W R, HedtjHedtjäärnrn, , ““Plastic scintillator Plastic scintillator response to lowresponse to low--energy photonsenergy photons””, Phys Med , Phys Med BiolBiol 44: 85744: 857--871, 1999.871, 1999.
• Direct measurement of the dose delivered to organs, critical structures, and within the vicinity of a tumor is feasible and can be used to verify treatment plan delivery.
• We believe this can be done using an in vivoscintillation detector composed of multiple probes arranged in an application-specific design that can monitor true in vivo dose in real time.
Urethral detector consisting of a capillary containing line and point probes for measurement of dose at the urethra. The outer diameter of the catheter is 2 mm (6F).
A single PSD is placed in an empty standard prostate plastic catheter. The remaining 12 catheters are used for planning and delivery The PSD is read in real-time to monitor the treatment delivery.
L. Archambault L. Archambault F.H. AttixF.H. AttixS.F. de BoerS.F. de BoerT.M. BriereT.M. BriereL. Gingras L. Gingras M. M. GuillotGuillotA. Ikhlef A. Ikhlef T.J. T.J. KinsellaKinsellaF. F. LacroixLacroix
T.R. MackieJ.F. RawlinsonJ.F. RawlinsonR. RoyR. RoyC.H. SibataC.H. SibataJ.V. J.V. SiebersSiebersF. F. ThThéériaultriault--ProulxProulxM. VilleneuveM. VilleneuveN. N. SuchowerskaSuchowerskaS. LawS. Law
…… and all others who have contributed to the field of and all others who have contributed to the field of scintillation dosimetryscintillation dosimetry