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