radioisotopes seminar

TATA MEMORIAL HOSPITALTMHTMH

DEPARTMENT OF RADIATION ONCOLOGY

RADIOISOTOPES USED IN BRACHYTHERAPYRADIOISOTOPES USED IN BRACHYTHERAPY

Dr.Vijay Palwe Dr. Gaurav Bahl



Brachytherapy

• Definition:

“Placement of sealed radioactive sources into or immediately adjacent to the target tissue is called as brachytherapy.”



History“Actually Radiotherapy started in the form of Brachytherapy”

1898 :

Marie & Pierre Curie isolated

Radium and work on

Brachytherapy started.



Robert Abbe (American surgeon ): First used Ra after loading technique for treatment of cancer.

1910 :1st text-book of Radium therapy Wickham & Degrais.1920-30s :major work in Paris “Paris System”

1930s : Meredith developed “Manchester System”

1934 :“Paterson-Parker”

History



• 1950-60s : Advent of mega voltage type tele-therapy machines had provided treatment option with non-invasive procedure; EBRT treatment.

• So, there was decline in progress of interstitial Brachytherapy.

Brachytherapy was considered ‘lost art’.

History



• 1964: Bernard Pierquin et al. used Ir192

after-loading interstitial implant.• 1980-90s : HDR after-loading , computer planning

& optimization came in use.

New possibilities in Interstitial Brachytherapy with advantages of HDR after-loading & computer optimization.

History



• According to dose rate 1) High dose rate (HDR)- - >12 Gy/Hr

(Usual dose rate of HDR Brachy.is 100-300 Gy/Hr)

2) Medium dose rate (MDR) - 2-12 Gy/Hr 3)Low dose rate (LDR) - - 0.4 -2 Gy/Hr 4)Ultra low dose rate (ULDR)- -0.01-0.3 Gy/Hr

Types of Brachytherapy



SOME BASIC DEFINITIONS• Radioactivity: No. of disintegrations per unit time (sec ,min,

hrs.) expressed in curies• 1 curie (ci)=3.7x1010 disintegration /sec• 1 Bequerel (Bq) =1 disintegration / sec. (S.I.unit)

• Half life(T1/2): “The time required for a radioactive isotope to lose half of its original activity .”

• Half Value layer (HVL): “The thickness of the specified substance that when introduced into the path of radiation coming from source, reduces the exposure rate at some point of measurement by one half.”



• Exposure Rate : Ionization equivalent of the kerma in air

• Exposure Rate constant: Exposure rate in R/h at a point from a 1mCi point source

• Formula: l2

Γδ = (dx/dt) A

• Dx/dt=exposure rate due to photon of energy greater than δ,at a distance l from a point source of activity A.

• Special Unit- Rm2h-1Ci-1



Properties of an IDEAL brachytherapy source (Godden,1988)

• Gamma ray energy high enough to avoid energy deposition in bone by photo-electric effect.

• Low enough to minimize need for radiation protection.

(ideal 0.2-0.4MeV)

• T1/2 such that correction for decay during Rx is minimal

• Absent / easily screened charge particle emission



• High specific activity eg. 192 Ir

• No gaseous disintegration product eg. radon

• Insoluble & non-toxic

• Not in powder form eg. Radium sulphate

• Can be made in different shapes eg. 192 Ir

• Perm. Implants- t1/2 should be short



Types of Radioisotopes depending upon type of emission

• γ emitters : 226Ra,222Rn,60Co,137Cs,192Ir,198Au,

125I,103Pd,169Yb,145Sm,241Am.

• β emitters : 32P,90Sr,90Y,106Ru,49Va,166Ho,144Pr

• neutron emitter: 252Cf



ISOTOPES USED IN BRACHYTHERAPY can be embedded in

• Surface Applicator- placed directly on surface of tumor eg. Hard palate, skin, ocular

• Intracavitory- inserted into specially designed apparatus that is placed into body cavity eg. Gynec.malign, nasopharynx

• Intraluminal- Various organs with lumen (Oesophagus, endobronchial, biliary etc.)

• Interstitial- Directly through tissues encompassing tumor• Intravascular- coronaries, peripheral art. internal mammary etc.



Application Traditional Current Future

Intracavitory---LDRHDR

Ra226Co60

Cs137Ir192

Am241,Ir192, Yb169Yb169,Ir192, Co 60

Interstitial ---Non after loading -After loading--HDR

Ra226------

Cs137Ir192Ir192

--I125, Pd103,Yb169Yb169, Ir192

Permanent implant –Conventional dose-rate-Ultra low dose rate--

Rn222--

Au198I125, Pd103

Au198, Cs131I125, Pd103

Intra vascular ---Cardiac stents—Catheter based cardiac—Catheter based peripheral -

--P32P32,Sr/Y90Ir192

?Yb169, Yu169,I125, Pd103, Yb169

Radioactive sources: Past, present and future



Element Isotope E(mev) T1/2

HVL Pb (mm)

Exposure rate constant Source

formClinical applicaion

Radium Ra226 0.83* 1626yrs

16 8.25 Tubes Needle

LDR ICA & Interstitial

Radon Rn222 0.83 3.83 day

16 8.25 Gas Perm. implant Temp. mould

Cesium Cs137 0.662 30 yrs

6.5 3.28 Tubes Needle

LDR ICA & Interstitial

Iridium Ir192 0.379 73.8 day

6 4.69 Seeds,Wires, ribbon

LDR/HDR

Cobalt Co60 1.25 5.26 yrs

11 13.07 Sphere HDR ICA

Iodine I125 0.028 59.6 day

0.025 1.45 Seeds PermanentImplant

Palladium Pd103 0.020 17 day

0.013 1.48 Seeds PermanentImplant

Properties of radioactive sources



Gold Au198 0.412 2.7 day

6 2.35 Seeds PermanentImplant

Sr / Y Sr90-Y90

2.24b 28.9yrs

- - Plaque Ocular

Americanum Am241 0.060 432 yrs

0.12 0.12 Tubes LDR ICA

Ytterbium Yb169 0.093 32 day

0.48 1.80 Seeds LDR Interstitial

Californium Cf252 2.4 n 2.65 day

- - Tubes High LET LDR ICA

Cesium Cs131 0.030 9.69 day

0.030 0.64 Seeds LDR Perm. Imp

Samarium Sm145 0.043 340 day

0.060 0.885 Seeds LDR Temp Interstitial

Element Isotope E(mev) T1/2

HVL Pb (mm)

Exposure rate constant

Source form

Clinical applicaion



RADIUM

• Earliest & once the most commonly used isotope• Naturally occuring • T ½ =1626 yrs• Disintegrates very slowly to hazardous radioactive gas Radon• At least 78 γ rays from Ra & its decay products of energy- ranging from

0.184 MeV - 2.45 MeV (avg.0.83Mev)• Some high energy β rays (max.3.26 Mev)• β filtration : 0.5 mm of Lead/ platinum• Has been widely used for intracavitary,interstitial & mould applications• Radium sulfate/Ra chloride mixed with inert filler & loaded in cell(1cm long

&1mm in dia.made of 0.1-0.2 mm thick Gold foil. )



0.66mg/cm

0.66mg/cm 1.0mg/cm

0.33mg/cm 0.66mg/cm

Uniform

Indian Club

Dumb bell

Tube

TYPES OF RADIUM NEEDLES



Uranium Ra Rn RaA RaB RaC Pb

α α α βγ βγ

T1/2 1620Yrs

3.83days

3.05min

26.8min

19.7minStable

Radium : provides constant source, replenishes decaying stock of Radon



Outer case(Pt+10%Ir)

Space forRa+filler mixture

Eyelet holecells

Wall thickness: 0.5mm of Pt+Ir alloy1mm of Pb to stop β

Gold foil : 0.1 mm thick Cells : used for loading

Physical characters of Ra 226 needles



NOW OBSOLETE because

• Leak of radioactive salt/gas

• High cost

• Difficulty in Disposal

• Better Radium substitute

• Produces hazardous radioactive gas Radon

• Specific activity low

• Mixture of several intermediate radioactive products-dose calculation error

can occur.



CESIUM 137: ( Cs137)

• Recovered from fission products made in Nuclear Reactor

• T1/2 : 30 yrs

• Relatively cheaper, extraction simple,

• Decay system :

• 55137 Cs 137

56Ba + 0-1e + γ

• No gaseous decay product, safer than Ra

• γ ray energy = 0.662 MeV

• Beta filtration – 0.5 mm Pt or stainless steel

• Available in tubes, needles, pellets.

• Replaced Ra in t/t of gynaecologic cancers.

Miniature cylindrical source



5mm

Active bead

(1.1mm dia.)

Stainless steel

1.8

Miniature cylindrical source

Miniature cylindrical source of CAESIUM 137: ( Cs137)



Spacer beads

Retaining spring

Min.cyl.sources

Spiral spring

Screw thread

Source train

Manual afterloading system of Cs

Source train consist of

flexible stainless steel holder containing

miniature source separated by

spherical steel spacers 1.8 mm in diameter.

Sources and spacers retained by a steel spring.



Cs 137 is incorporated in glass bead & encapsulated

in stainless steel ball bearing. which with inactive

spacer beads, can be pneumatically loaded from

intermediate safe to pt. applicator.

Remote afterloading system of Cs

2.5mm



IRIDIUM 192 (192Ir)

• Produced in Nuclear reactors.• T1/2 =73.8 days• Decays through β emission and electron capture to 192Pt and 192Osmium

• Decay scheme: 192I 192 Pt+ 0-1e+ γ

• Emits 11 γ rays of energies ranging from 0.136 to 0.613 MeV• Effective γ rays energy is appr. 0.380 MeV• Emits β particles max energy 0.670 MeV• β filtration =0.1mm of platinum• (Eliminated by stainless steel capsule)• HVT- 4.5mm of Lead (Pb)• Available in nylon strands or as platinum cladded wire.



PHYSICAL PROPERTIES OF 192Ir seed

•Seeds are 3mm long & 0.5 mm in dia.

•Internal diameter core of 30%Ir +70%Pt

surrounded by 0.2 mm thick stainless wall



192 Ir wire( coil form) Single Pin Hair Pin

Physical forms of 192Ir-Core dia 0.1mm 0..4mm

Sheath thickness 0.1mm 0.4mm

Overall 0.3mm 0.6mm

Wire Hair pins



GOLD (198Au)

• Produced in Nuclear reactor when 197Au absorbs one neutron

• Emits primarily Y rays

• Energy 0.412 MeV (monoenergetic)

• T1/2 = 64.7 hrs ( 2.7 days)

• Available in seeds and grain forms encased in Pt (0.1mm) filters β radiation.

• Suitable for permanent implants ( Short half life)

• Replaced Radon seeds in permanent implants

• Protection problem easily solved ( Emit only 3Y rays in contrast to complex

spectrum of Ra & also lower y energy)

• Also prepared in colloidal form for t/t of ascitis due to intraperitoneal tumors.



IODINE( 125I)• Produced in Nuclear reactors• Used in permanent implants & can also be used in removable implants.

• T1/2 = 59.6 days

• Y ray photon Energy = 0.274 MeV & 0.355 MeV• Decay scheme = electron capture • 124Xenon 125I 125Telleurium • Adv over Rn & Au –longer t1/2

-convenient for storage

- low photon energy, less shielding .

But- dosimetry is much complex

& most T/t planning systems doesn’t take anisotropy

in account



Types of Iodine 125 implants

• Type 6702: used in temporary interstitial implants• Consists of welded Titanium capsule containing 3 resin spheres onto which

125I is adsorbed by ion exchange.• Sources available in air kerma rate at 1 m of 6.4-51.9 μGy h-1

• Effective energy 28.5 kev

0.8mm

4.5mm

125 I adsorbed on ion exchange resin 0.05 mm Titanium



Type 6711• Used in permanent implant• Consists of welded titanium capsule containing I 125adsorbed onto a silver

rod (which also act as x ray marker)• Active length=3mm & dia. 0.5 mm• Overall length = 4.5mm & dia.0.8mm• Sources available with air kerma rate of 1m of 0.13-7.58 μGy h-1

0.8mm 0.5mm

3.0mm4.5mm



Model 2300 of 125I

• Radioactive Iodine adsorbed on a tungston wire that is encapsulated by 2 walls of titanium

• Suitable for both temporary & permanent implantations as available in wide range of source strengths.

• Tungston wire –radiographic marker

• Double walled encapsulation –reduces risk of radioactive leakage



PALLADIUM 103 (103 Pd)

• Produced in nuclear reactors when stable 102Pd absorbs a neutron.• Decay scheme = via electron capture ( 1st & 2nd excited states of

Ruthenium103)• T1/2 = 17 days• Photon energy = 21 kev• Useful in permanent implants• HVL for Lead= 0.008 mm• Substitute for 125I (shorter half life)• Available in form of seeds• Used in prostate implants



0.8mm

4.5mm

Titanium end cup Lead Xray markerPd plated grafite pelletLaser weld

103Pd seed



COBALT 60 (60Co)

• Produced by neutron activation of stable isotope 59Co

• Decay scheme: 6027Co 60

28Ni+ -1 0e + y

• T1/2 = 5.26 yrs• Each disintegration produces 2 y rays of energy 1.33 & 1.17 MeV

(avg energy 1.25 MeV)• β energy= 0.318 MeV• HVL in Lead = 10 mm• Relatively high penetrating power makes an excellent isotope in teletherapy.• Recently used in opthalmic plaques for t/t of ocular melanomas &

retinoblastomas.• Activity higher , can be used in brachytherapy.



Reasons for re-emergence of 60Co as brachytherapy source

• No need for frequent replacements • Cost effective• Miniaturised,(same size of conventional Ir192 source)• High activity• Low operating cost.



STRONTIUM 90 (90 Sr) & Yttrium90 (90Y)

• 90Sr decays through β ray emission to 90Y• 90Sr always coexist in equilibrium with radioactive daughter 90Yttrium• T1/2=28 yrs• Max β ray energy =0.54 MeV• Dose falls very rapidly away from the applicator & is appr.20% at 2mm depth

in tissue.• Dose rate on surface in range of 100 cGy /S thus t/t delivered in seconds• Used in corneal ulcers, pterygium, corneal vascularization & neoplasms.• Yttrium in colloidal preparations used in malignant effusions.• Yttrium pellets in pituitary gland to abolish its secretary activity in hormonal

control of breast cancers.• Yttrium used in SIR (selective internal radiation) in liver malignancies.• 89Sr (non-sealed) used in t/t of bone mets.



PHOPHORUS 32 (32 P)

• Unsealed radioisotope• Produced in nuclear reactor by neutron bombardment of sulfur,• Pure β-emitter• Max β energy =1.71 MeV• T1/2 =14.7 days• Formerly used in t/t of polycythemia vera & other hemat. malignancies• Also in t/t of superficial warts, basal cell ca, angiomas.• Now used in intrapleural, intraperitonial instillations.• 32P coated stents - used in t/t of arterial restenosis.



CALIFORNIUM 252 (252Cf)

• Neutron emitter (Radiobiological superiority)• Production from multiple neutron capture by 238U• Decay scheme – alfa emission• Produces charged particles, gamma rays & neutrons• T1/2=2.63 yrs• Neutron energy= 2.3 MeV• Typical source -0.25ug – 0.45ug (each ug emits 2.34 x106 neutrons)• Available in seeds or tubes form• Used in ca cervix LDR ICA



NEWER ISOTOPES IN BRACHYTHERAPY



RUTHENIUM 106 (106 Ru)• Fission by-product

• Decay scheme- β emission

• Max energy -0.039 MeV, avg.energy-0.009 MeV

• 106Ru 106Rh + β

• T1/2=368 days

• 106Ru in radioactive equilibrium with daughter 106Rh

• Used in shallow opthalmic lesions



VANADIUM 49( 49 Va)

• Produced through (p,n) reaction with 48Ti

• Emits positrons & gamma rays

• Positrons avg energy -0.696MeV , y ray avg energy- 0.511 MeV

• T1/2= 16 days

• Stent being utilized for intracoronary applications



HOLMIUM166 (166HO)• Produced through (n,y) reaction with 165 Ho

• Decay scheme-β emission

• 166Ho 165 Ho+ β 166Er(stable)

• Max β energy= 1.9 MeV (avg 0.63)

• T1/2=27 hrs

• Considered for intravascular brachytherapy



PRASEODYMUM 144 (144 Pr)

• Fission byproduct of Cerium144

• Decay scheme –β emission

• T1/2 =285 days

144Pr 144Ni+ β

• Max β energy 3 MeV (avg 1MeV)

• Considered for intravascular brachytherapy.



THANK YOU

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