Quimby-based Brachytherapy Systems · Quimby-based Brachytherapy Systems Robert D. Zwicker...
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Transcript of Quimby-based Brachytherapy Systems · Quimby-based Brachytherapy Systems Robert D. Zwicker...
QuimbyQuimby--based based BrachytherapyBrachytherapySystemsSystems
Robert D. ZwickerRobert D. ZwickerRadiation Medicine DepartmentRadiation Medicine Department
University of KentuckyUniversity of Kentucky
ClassicalClassical BrachytherapyBrachytherapy SystemsSystems
•• QuimbyQuimby (1932): uniform Ra(1932): uniform Ra--226 226 activity distributionactivity distribution
•• PatersonPaterson--Parker (1934): heavy Parker (1934): heavy peripheral loading of Raperipheral loading of Ra--226226
•• Paris (1978): uniform IrParis (1978): uniform Ir--192 wire 192 wire loadingloading
QuimbyQuimby System (E. System (E. QuimbyQuimby, 1932), 1932)
•• Equally spaced RaEqually spaced Ra--226 needles226 needles•• Planar or Volume distributionsPlanar or Volume distributions•• Tables of exposure rates along a central Tables of exposure rates along a central
line perpendicular to implant planeline perpendicular to implant plane•• Tables of exposure rates at periphery of Tables of exposure rates at periphery of
volume implantvolume implant•• Concepts applied to IrConcepts applied to Ir--192 implants192 implants
QuimbyQuimby System: planar dose System: planar dose distributiondistribution
•• For points equidistant from implant For points equidistant from implant plane, dose rate is higher near the plane, dose rate is higher near the centercenter
•• IsodoseIsodose curves bulge outward near curves bulge outward near the center of the plane the center of the plane
QuimbyQuimby--type type planar implantplanar implant
From C. Saw and N, From C. Saw and N, SuntharalingamSuntharalingam, Med. Phys , Med. Phys
15: 391, 198815: 391, 1988
QuimbyQuimby System: System: biplanarbiplanar implantsimplants
•• QuimbyQuimby mainly concerned with mainly concerned with surface applicatorssurface applicators
•• No effective guidance for multiple No effective guidance for multiple plane implantsplane implants
•• Two plane implants hotter near Two plane implants hotter near center, cooler at edgescenter, cooler at edges
•• Central minimum dose typically 25Central minimum dose typically 25--30% hotter than prescription dose30% hotter than prescription dose
TwoTwo--plane Irplane Ir--192 192 QuimbyQuimby implant:implant:(a) central plane (a) central plane between sourcesbetween sources(b) central plane (b) central plane bisecting sourcesbisecting sources
From R. Zwicker and R. SchmidtFrom R. Zwicker and R. Schmidt--UllrichUllrich, IJROBP 31: 149, 1994, IJROBP 31: 149, 1994
QuimbyQuimby System: Volume System: Volume ImplantsImplants
•• Uniform sources 1 to 2 cm apart Uniform sources 1 to 2 cm apart throughout implant volumethroughout implant volume
•• Tables of source strengths published Tables of source strengths published for minimum of 1000 for minimum of 1000 cGycGy at volume at volume peripheryperiphery
QuimbyQuimby based systems using based systems using IrIr--192 seeds in ribbon192 seeds in ribbon
•• Kwan System (Kwan et al.)Kwan System (Kwan et al.)•• Memorial System (Anderson et al.)Memorial System (Anderson et al.)•• Tufts System (Zwicker et al.)Tufts System (Zwicker et al.)•• Saw System (Saw et al.)Saw System (Saw et al.)
Kwan System (Kwan et al., 1983)Kwan System (Kwan et al., 1983)
•• Two plane implants, uniform distribution of Two plane implants, uniform distribution of IrIr--192 seed activities192 seed activities
•• Examined ratio of peripheral (A) to central Examined ratio of peripheral (A) to central (B) dose(B) dose
•• Studied positioning of sources inside Studied positioning of sources inside volumevolume
•• Studied Studied interstrandinterstrand and and interplanarinterplanarspacing (1.0 and 1.5 cm)spacing (1.0 and 1.5 cm)
Kwan Kwan system: system:
source and source and calculation calculation
point point positionspositions
From Kwan et al, Med. From Kwan et al, Med. Phys. 10, 456, 1983Phys. 10, 456, 1983
Kwan System: Kwan System: interstrandinterstrand
and and interplanarinterplanarspacingsspacings
From Kwan et al, Med. From Kwan et al, Med.
Phys. 10, 456, 1983Phys. 10, 456, 1983
Kwan Kwan System: System:
dose dose uniformityuniformity
From Kwan et al, Med. From Kwan et al, Med. Phys. 10, 456, 1983Phys. 10, 456, 1983
Kwan System: ConclusionsKwan System: Conclusions
•• Extend sources to lateral boundaries of Extend sources to lateral boundaries of target volumetarget volume
•• Use 1.5 cm Use 1.5 cm interstrandinterstrand and and interplanarinterplanarspacingspacing
•• Dose rate curves given for 2.0 cm target Dose rate curves given for 2.0 cm target thickness (x 0.87 for 2.5 cm)thickness (x 0.87 for 2.5 cm)
•• Equivalent square used for rectangular Equivalent square used for rectangular implantsimplants
Memorial System (Anderson et al)Memorial System (Anderson et al)
•• Devised for use with inDevised for use with in--house stocks of Irhouse stocks of Ir--192192•• BiplanarBiplanar implants, reference point near cornerimplants, reference point near corner•• InterplanarInterplanar separation 1.5 cm, target thickness separation 1.5 cm, target thickness
2.5 cm2.5 cm•• one fewer strand in superficial planeone fewer strand in superficial plane•• NomographNomograph gives number of strands for 10 gives number of strands for 10
GyGy/day/day•• Similar ISimilar I--125 125 nomographnomograph widely used for widely used for
prostate implantsprostate implants
Memorial Memorial System: System: IrIr--192 192
nomographnomograph
from L. Anderson and A. from L. Anderson and A. OsianOsian, , Endocuriether/HypEndocuriether/Hyp
OncOnc. 2: 5, 1986. 2: 5, 1986
Tufts System (Zwicker et al, 1985)Tufts System (Zwicker et al, 1985)
•• Considers range of target thicknessesConsiders range of target thicknesses•• InterplanarInterplanar separation varied with target separation varied with target
thicknessthickness•• Reference dose extends to target Reference dose extends to target
boundaries along symmetry axesboundaries along symmetry axes•• Tables of plane separation and dose rates Tables of plane separation and dose rates
givengiven
Tufts System: (a) central plane between Tufts System: (a) central plane between source planes; (b) central plane bisectingsource planes; (b) central plane bisecting
source ribbons; target volume = source ribbons; target volume = WLtWLtFrom R. Zwicker et al, IJROBP 11: 2163, 1985From R. Zwicker et al, IJROBP 11: 2163, 1985
Saw Method (C. Saw et al, 1988)Saw Method (C. Saw et al, 1988)
•• Examined choice of reference dose rate Examined choice of reference dose rate for varied implant geometriesfor varied implant geometries
•• Studied single and two plane implantsStudied single and two plane implants•• Used coverage (CI), homogeneity (HI), Used coverage (CI), homogeneity (HI),
and external volume (EI) indicesand external volume (EI) indices•• Found maximum in HI for a given (optimal) Found maximum in HI for a given (optimal)
reference dose ratereference dose rate•• Provided plots of optimal reference dose Provided plots of optimal reference dose
rate versus implant sizerate versus implant size
Saw Method: Saw Method: biplanarbiplanar implant area (a) 3x3 cm;implant area (a) 3x3 cm;(b) 6x6 cm; (c) 9x9 cm; (d) 12x12 cm(b) 6x6 cm; (c) 9x9 cm; (d) 12x12 cm
From C. Saw and N. From C. Saw and N. SuntharalingamSuntharalingam, Med. Phys. 15: 391, 1988, Med. Phys. 15: 391, 1988
Saw Method: Saw Method: optimized dose optimized dose
rate, CI, HI, rate, CI, HI, and EIand EI
From C. Saw and N. From C. Saw and N. SuntharalingamSuntharalingam, Med. Phys. 15: , Med. Phys. 15:
391, 1988391, 1988
ConclusionsConclusions
•• QuimbyQuimby--based implants widely used in based implants widely used in LDR LDR brachytherapybrachytherapy
•• Need for dose rate/activity tables, plots, Need for dose rate/activity tables, plots, nomographsnomographs eliminated by availability of eliminated by availability of computer planning computer planning
•• Understanding of characteristics of Understanding of characteristics of QuimbyQuimby--based implants is useful in based implants is useful in modern treatment planningmodern treatment planning