RADIOACTIVITY-NATURAL & ARTIFICIAL RADIOACTIVE ISOTOPES-PROPERTIES &

CLINICAL USES

DR.SUGASHWARAN.J MODERATOR:DR.SATHIYAN,

DEPT OF RADIATION ONCOLOGY, KMIO,BANGALORE.

RADIOACTIVITY• Radioactivity is the property of certain

substances to undergo spontaneous disintegration, with emission of particle or energy in form of electromagnetic energy due to instability of the nucleus.

• Radioactivity was first discovered in 1896 by the French scientist Henri Becqueral while working on phosphorescent materials.

• The change from one nucleus to another is called as disintegeration.

• Total 118 elements discovered till now• Most of them are stable.

RADIOACTIVITY

PROPERTIES.• It cannot be altered in any way by

any known agent• It is unaltered by any chemical

combination in which it may be found• Rate of decay of a particular

radioactive material is the same irrespective of variations in temperature or pressure.

• It is same for freshly prepared & for very old material

• It can never be switched off

RADIOACTIVITY

NATURAL

• The phenomenon of spontaneous emission of rays by heavy elements having atomic number greater than 82

• Eg: Radium-226

ARTIFICIAL

• This nucleus produced by bombardement of particle

• Emits electrons, neutrons, positrons and gamma rays

• Eg: Cobalt-60, Phosphorus-32

• Discovered by Curie and Juliet in 1934

RADIOACTIVE DECAY• Radioactive Decay is a process by

which unstable nuclei reach a more stable configuration.

• Alpha particle decay• Beta particle decay• Gamma emission• Electron capture• Internal conversion• Isometric transition

ALPHA DECAY• Radioactive nuclides with very high atomic

numbers decay mostly with the emission of α particle with a mass number 4 less and atomic number 2 less , have 4 to 8 Mev energy.

• 88Ra226 → 86Rn222 + 2He4 + α ray (4.87MeV)

BETA DECAY• The process of radioactive decay, in which

an electron or positron is ejected is called the β decay.

• Electron emission – β- decay• Positron emission – β+ decay

• Beta negatron: high neutron proton ratio, originates from the nucleus like alpha emitters. neutron in the nucleus changes to a proton, increasing the atomic number by one.

3215P ---> 32

16S+ B- + e- + v(+1.71 Mev)

• Beta positron: low neutron proton ratio, comes from the nucleus which has too many protons. proton in the nucleus changes to a neutron, decreasing the atomic number by one.

3015P ---> 30

14Si + B+ + e+ + v(+3.3 Mev)

• Annihilation radiation: When positrons are released they quickly combine with electrons and both disappear, their masses being converted to two photons of electromagnetic radiation. Both have energy of 0.511 MeV.

GAMMA EMISSSION• After emission of alpha or beta particles if the

daughter is still excited, it emits the excess energy in the form of electromagnetic rays( photons) or gamma ray.

• 6027Co ---> 60

28Ni + B- +gamma• Gamma rays of 1.17 MeV and 1.33 MeV are

produced. • Do not affect the mass no or atomic no.ELECTRON CAPTURE• It is an alternative to positron decay• when atom doesn’t have sufficient energy for β+

decay. atom captures a k shell electron to convert a proton into neutron.

• empty hole in the involved shell filled by outer electron characteristic x rays.

• e.g. Cr-51, Fe-55, I-125

ISOMETRIC TRANSITION• After alpha or beta emission by the parent,

sometimes the daughter remains in excited state for sometime i.e. for hours to days. It is said to be in metastable state. Later it emits photons or gamma rays to achieve a stable configuration.

• Mo-99-----------> Tc 99m + -1 β 0

(67hrs) (6hrs)• Tc 99m------------>Tc 99 + γ

RADIOACTIVE SERIES• Naturally occurring radioactive elements grouped

into 3 series : Uranium , Actinium, Thorium.

• U238 ---------------> Pb206 4.51 x 109 yr

• U235 ---------------> Pb207 7.13 x 108 yr

• Th232--------------> Pb208 1.39 x 1010 yr

RADIOACTIVE EQUILIBRIUM • parent nuclei --------------> daughter nuclei (radioactive) (radioactive)• if half life of parent is longer than that of daughter,

then after certain time a condition of equillibrium will be achieved.

• Ratio of parent activity : daughter activity = constant

TYPES • secular equilibrium: parent t1/2 >>>>>>>>

daughter t1/2

e.g. 88

Ra226 _________________ 86

Rn222 + 2 He4

• transient equilibrium: parent t1/2 >> daughter t1/2

e.g. Mo-99-----------> Tc 99m + -1 β 0

RADIOISOTOPES IN CLINICAL MEDICINERADIOISOTOPES• If two atoms of an element are having same

atomic no (Z) but differ in their atomic mass(A) then those two atoms are called as isotope of each other and if atom is having property of radioactive emission it is called as radioisotopes.

Mainly used• As gamma ray sources for teletherapy and

brachytherapy• For ‘tracer’ studies for diagnostic and research

purposes• For internal administration for therapeutic

purposes

ISOTOPES IN MEDICINETHERAPYDIAGNOSIS

internal external in vitro in vivo

systemic sources tele radio14C3H125I

others

99Mo-99mTc

201Tl 123I111In67Ga

81Rb-81mKrothers

ß+ emittersfor PET

18F, 11C,13N,15O86Y, 124I

68Ge-68Ga82Sr-82Rb

131I,90Y153Sm,186Re188W-188Re

166Ho,177Lu, others

a-emitters:225Ac-213Bi

211At, 223Ra 149Tb

e--emitters:125I

sealed sourcesand

applicators:192Ir, 60Co,

137Csothers

seeds forbrachytherapy:

103Pd, 125I

microspheres90Sr - 90Y, others

60Co-Tele

cobalt

gammaknife

137Cs- Tele

cesium

IDEAL ISOTOPESTELETHERAPY SOURCES

• Easily available and cost effective.

• High energy• Moderate gamma

ray constant (determines activity & output)

• High specific activity availability (Ci/gm) to allow fabrication of smaller sources & to achieve higher output

• Long half life of source and container (10 yrs)

• Disposable without radiation hazard to environment

• Low self attenuation

BRACHYTHERAPY SOURCES• Photon energy :low to

medium i.e. 0.03 to 1MeV

• Moderate gamma ray constant

• High specific activity availability (Ci/gm)

• Isotropic: same magnitude in all directions around the source

• Long half life of source- temporary

• Permanent implants need fairly short half life to minimize precaution

• Material available in insoluble & non-toxic

• Sources can be made in different shapes & sizes: Tubes, needle, wire, rod, beads etc.

• Absence of charged particle emission or it should be easily screened

CLASSIFICATION ACCORDING TO EMITTERS• Beta emitters(pure) H-3, P-32• Gamma emitters(pure) Cr-51, Fe-55,

Se-75, Sr-85, Sr-87m, Tc-99m, In-113m, I-125, Hg-197, Co-57

• Gamma & beta emitters Na-24, Fe-59, Co-60, I-131, I-132, Xe-133, Au-198

• Positron emitter F-18• Positron & beta emitter Co-58• Alpha emitters (beta & gamma)Ra-

226,Rn-222

RADIUM-226• Discovered by Marie Curie in 1898.• Sixth member of the radio active series which

starts with uranium and ends with lead.• Isolated from Pitchblende ore.• Half life 1600 years• 49 different gamma rays from 0.184-2.45 MeV• Gamma energy 0.83 MeV• Half value 12mm Pb• ERC:8.25 Rcm2/mg-h• Filtration 0.5-1mm Pt• Mostly in the form of radium sulfate or

chloride crystals• Filler used is magnesium oxide.

RADIUM_226• Outer case platinum alloy with 10% iridium, sealed

container.• Thickness needles- min 0.5mm (0.6mm), tubes- 1

mm• Cell loading system – Cell length 1 cm, 1 mm

diameter, Cell made up of 0.1-0.2 mm gold.SOURCE FORMS• Uniform intensity can be full/half/quarter intensity (0.66/0.33/0.165mg/cm)• Dumbbell has high activity at both ends (0.66) and middle(0.33)• Indian club has more activity at one end. (1mg/cm) rest uniform of 0.66mg/cmNeedles with 0.5 and 0.25 mg/cm and tubes with

multiples 5mg radium were also available

RADIUM-226SOURCES AND USE • Tubes- moulds skin tumors, intracavitary treatment• Needles- implant nasopharynx ,oral cavity, different

from tube with pointed end only.DISADVANTAGES• Radium and its daughter products are alpha ray

emitter • Radon is noble gas readily soluble in tissue• Cannot be incinerated• Large radiation protection needed for high gamma

energy• Such high energy not required for brachytherapy so

thickness of source increases.• Transportation• Heavy protection screens• Heavy rectal shields for intracavity application• Practical maximum activity concentration low

unsuitable for afterloading systems.

RADON-222• Half life 3.83 days• Photon energy 0.83 MeV• HVL 12 mm Pb• ERC:10.15 Rcm2/mg-h• Extraction complex• Gas encapsulated gold tubings and

seeds• Used in LDR permanent implants and

temporary moulds

CESIUM-137• 1956, by brucer.• Half life is 30 years• Monoenergetic gamma ray emitters,

energy of 0.662 MeV• HVL 6.5mm• Beta particle of low energy 0.51MeV• Fission product of nuclear reactor• Extraction simple• Barium product

CESIUM-137• Filtration 0.5mmPt or o.5mm stainless steel• Unfiltered cesium ERC:3.26 Rm2/mCi-h• Conversion factor w.r.t to radium is 2.53 mCi of Cs137

per mg of Ra226

• Amersham model CDCS-J tube-13.5mm active length, 20mm physical length, 2.65mm physical diameter, capsule of 0.5mm thickness, LDR intracavity source.

• Needles used in place or radium for temporary manual afterloading LDR interstitial implants. Tubes have almost replaces radium tubes with external diameter 1.5-2.., active length 3-4.5mm and capsule of alloy of .5-.65mm.

SOURCE FORMS• Cylindrical –manual after loading.• Spherical pellet – selectron remote afterloading• Use - LDR intracavity, vaginal, intra uterine and interstitial brachytherapy train of sources.

COBALT-60• By neutron activation • Half life 5.26 years• Decays to nickel• Beta energy 0.318 MeV• Photon 1.25 MeV (1.17 and 1.33)• HVL 11.0 mm• Pt-Ir or stainless steel• High specific activitySOURCE FORMS• Needles ,pellets,Tubes• Curie size cobalt unit- cathethron• Encapsulated spheres in HDR brachytherapy.• Teletherapy 1952 Canada by Johns

IRIDIUM-192• 1960• Neutron activation of

stable Ir 191.• Easily available pure raw

material.• Large neutron capture

surface area.• No significant

contaminant isotope.• Half life 73.8 days• Beta energy 0.079-

0.672mev• Photon energy 0.38MeV• Filtration 0.1mm

platinum• HVL 4.5 mm• 4.69 Rcm2 /h-mCi• Thin flexible source

SOURCE FORMS• Wires - closed

radiation source.

• Hair pins.• Seeds• Ribbons• Miniature

sources .

IRIDIUM-192USE• Seeds in nylon ribbon – LDR temporary interstitial

implant, intravascular brachytherapy ( cardiac)• Metal wires - LDR temporary interstitial implant,

returned to vendor after 1-3 patients use.• Encapsulated miniaturized source on cables- HDR

interstitial and intracavity brachytherapy, intravascular peripheral brachytherapy.

IRIDIUM WIRE• Platinum covered Ir 192 supplied in 500 mm

length coils with core of 0.1mm thick, encased in a sheath of platinum, 0.1mm thick

• known as a closed radiation source• Wire is cut to the required length and loaded into plastic tubes or hypodermic needles• Air kerma rate - 4.19mGy/h• Clinically used in after loading interstitial implants.

IRIDIUM-192HAIRPIN• Used by Guide-Gutter Technique in smaller

intraoral lesions esp. small tumors of mobile portion of tongue, FOM; Anal regionSEEDS• Two types of seeds1)Active dia 0.3 mm, Length and outer dia 3mm and 0.5mm2)Active dia 0.01mm Iridium seeds encapsulated on nylon ribbon of diameter of 0.8mm, spaced at 1-0.5cm center to center distance

IRIDIUM-192MINIATURE Ir-192 SOURCES FOR HDR• HDR radionuclide of high specific activity needed =

12 gray/ hr without limiting miniaturization.• Max specific activity depend on

No of atoms per gram Neutron capture cross section of target Neutron flux of reactor Purity of target and product

• Decay time of product.• Diameter: 0.2 to1.3 mm (1.1mm)• Active length: 1 -20 mm (4.5mm)• Air kerma rate of 42 mGy/hr• Active wire is encased in stainless steel. • In recent time a smaller slightly dimension 4.95

mm length and 0.9 mm diameter source with similar dose

distribution available.

GOLD-198• Nuclear reactor product.• Half life 2.7 days• Short half life so permanent implant.• Mainly gamma emitter –0.412 MeV β energy 0.96MeV• HVL 2.5mm, 0.1mm platinum• Gold seed typical 2.5 mm long with an outer

diameter 0.8 mm. Clinically used in LDR permanent implant as option for radon

• Disadvantage – exposure to using personnel - confinement of the patient. - short half life.

IODINE-125• Neutron activation of xenon -125• Half life 59.4days• 125I decays by electron capture and internal

conversion process give rise to 27 to 35KeV.• Tenth value layer 0.01mm lead• Sources in forms seeds• Highly anisotropic• Model 6701- I125 absorbed on a tungsten wire

encapsulated by two walls of titanium.• MODEL 6702- form of iodide ions• High intensity seeds model 6711-22.1KeV

and 25.2KeV

IODINE-125• Advantages:

– More isotropic, – Wide range source, – Wire radio graphic marker– Less chance of leakage.

• Advantage of I125 over gold198 – Long half life,– Convenient storage,– Low photon energy so less shielding.

• Disadvantage – high cost as compared to iridium seeds.

- Highly anisotropic• Clinically used for Ultra low dose permanent

interstitial implants prostate.• LDR temporary interstitial implant as episcleral

Plaque in treatment of choroidal melanoma

PALLADIUM-103• 1988, MODEL 200 • Neutron bombardment of Palladium 102 • Half life 17 days• Decay by electron capture, mostly to Ruthenium-103

and liberates Auger electron. • Effective energy 20.9 KeV(20 to 23 KeV)• Tenth value layer 0.03 mm Pb • Biological advantage in permanent implant because the dose is delivered at a faster rate.• RBE 1.3 to 1.5.• Used as ultra low dose permanent implant in early stage prostate cancer.• Active material is coated onto a graphite pellets 0.9mm

long• and 0.6mm diameter, between is 1mm lead marker.• Seeds are encapsulated in a 0.05 mm thick titanium

tube which is Laser welded.

CESIUM-131• 0.03MeV• 9.69days• 0.03 mm HVL• 0.64 Rcm2/mCi-h• Seeds tried in

permanent implant.

• Under development

TANTULUM-182• 0.18 – 0.5 MeV• 6.87 Rcm2/mCi-h • Half life 115 days• HVL 12 mm Pb• Source form :

Wires• Temporary

interstitial implants

STRONTIUM-90

• Energy 0.54-2.27MeV• Half life 28.9 years• HVL 0.14mm lead• Temporary application for shallow ocular lesion . e.g. pytregium• Source form is a plaque• Seeds tried in intravascular

brachytherapy.

SAMARIUM-145• Photon energy 38.2 - 61.4 MeV• Half life 340 days• Maximum specific activity 73 GBq/mm3 • Tenth value layer in lead 0.2 mm• To improve dose distribution and shelf life

compared to I125

• In addition photon energy emitted allows sensitization of cells to radiation damage by the addition of iodinated deoxyuridine.

• Tried as seeds in LDR temporary implants

CALIFORNIUM-252• Decay by alpha emission• Half life – 2.65yrs• Give particle radiation neutron 2.1-2.3 MeV • Gamma energy- 0.5-1Mev• RBE neutron = 6 so bulky gynecological

tumors can be better treated by high LET, esp. in hypoxia

• Rapid dose wall will maintain acceptable late complications.

• Has been tried as high LET LDR intracavitary tubes.

• Clinically no difference, still experimental• Costly, more complex radiation protection

and handling• More hazard to doctors using it.

AMERICUM-241• Energy 13.9-125 KeV, dominant is 60 KeV• Half life 432 years• Maximum specific activity 0.34 GBq/mm3• Tenth value layer of lead 0.42mm• Rectal shield by 50% dose need 0.2mm

lead foil• Disadvantage : alpha emitter, only low

specific activity available• Alternative to Cs137 for Ca Cervix and Ca

Endometrium.• As tubes in LDR intracavity

brachytherapy

YETTERBIUM-169• Energy 100 KeV• Half life 32 days• Thin 0.4mm lead shield for rectum

and bladder • Maximum specific activity 340

GBq/mm3

• so highly miniaturized LDR source seeds and HDR sources possible.

• Less attenuation in tissue than I125 and Pd103 and high specific activity

• LDR temporary interstitial implants as plaque for treatment of choroidal melanoma.

• Future role in HDR source, intraoperative and intravascular brachytherapy.

• USE gynecological intracavity treatments.

• Commercially not available

Radiobiological supplementation

• High RBE/LET• Use in hypoxia• Palidium103• Samarium 145• Americunum241• Yttrium 169 • Energy in kev so more effective

theoretically, but none effective in hypoxia

• All tested, only palladium useful in prostate implant

• Very costly, only USA, short half life

DIAGNOSTICS

• Thyroid function test. I-132

• Renal function test. I-131 labeled ortho- iodohippurate.

• Pernicious anemia-radioactive cobalt labeled vitamin b 12.

• Red cell survival- Cr51

• Melanoma detection P32.

• Thyroid scans I-131 Tc99m

• Brain Tc99m• Liver I-131 Tc 99m

THERAPEUTICS

• Thyroid disease- I-131

• Bone marrow irradiation and whole body irradiation- P-32

• Radioactive gold 198 malignant pleural effusions.

RADIOISOTOPE IMAGING organ Isotope used / activity

brain In-113m / 7-10mCi

kidney Hg-197 / 150mCilungs Tc-99 / 1mCi

I-131 / 0.15-0.3mCiIn-113 / 1mCi

spleen Cr-51 / 0.3mCi

bone Sr-85 / 0.1mCiSr-87 / 1mCiF-18 / 1mCi

pancreas Se-75 / 0.2mCi

placenta Cr-51 / 0.05mCiTc-99 / 0.5-1mCi

METABOLISM USEIsotope used/ activity

Labeled material & technique

Interference

Fat metabolism I-131/ .025-.05mCi Trioliumorally

%of dose excreted in feces over several days

Gastrointestinal blood loss

Cr-51/ .03-.04mCi RBCI.V

Activity in feces

Iron metabolism Fe-59/.003-.01mCI Ferrric citrate Rate of disappearance from plasma is index of erythropoiesis

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