This document provides information on radioactivity and radioactive isotopes used in clinical medicine. It discusses the properties of natural and artificial radioactivity and types of radioactive decay. Common medical radioisotopes used for therapy and diagnosis like radium-226, cesium-137, cobalt-60, iridium-192, gold-198, and iodine-125 are described in terms of their production, half-lives, emissions, and clinical applications and source forms. The ideal properties of radioisotopes for use in teletherapy and brachytherapy are also summarized.

1. RADIOACTIVITY-NATURAL & ARTIFICIAL
RADIOACTIVE ISOTOPES-PROPERTIES &
CLINICAL USES
DR.SUGASHWARAN.J
MODERATOR:DR.SATHIYAN,
DEPT OF RADIATION ONCOLOGY,
KMIO,BANGALORE.

2. 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.

3. 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

4. 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

5. 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

6. 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 βdecay.
• Electron emission – β- decay
• Positron emission – β+ decay

7. • 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.
32
15P ---> 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.
30
15P ---> 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.

8. 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.
• 60
27Co ---> 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

9. 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

10. 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

11. RADIOISOTOPES IN CLINICAL MEDICINE
RADIOISOTOPES
• 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

12. ISOTOPES IN MEDICINE
THERAPYDIAGNOSIS
internal externalin vitro in vivo
systemic sources tele radio14C
3H
125I
others
99
Mo-99m
Tc
201Tl
123I
111In
67Ga
81Rb-81mKr
others
ß+ emitters
for PET
18F, 11C,13N,15O
86Y, 124I
68Ge-68Ga
82Sr-82Rb
131I,90Y
153Sm,186Re
188W-188Re
166Ho,177Lu,
others
a-emitters:
225Ac-213Bi
211At, 223Ra
149Tb
e
--emitters:
125I
sealed sources
and
applicators:
192Ir, 60Co,
137Cs
others
seeds for
brachytherapy:
103Pd,
125I
microspheres
90Sr - 90Y, others
60Co-
Tele
cobalt
gamma
knife
137Cs-
Tele
cesium

13. IDEAL ISOTOPES
TELETHERAPY 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

14. 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

15. 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.

16. 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/cm
Needles with 0.5 and 0.25 mg/cm and tubes with multiples
5mg radium were also available

17. RADIUM-226
SOURCES 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.

18. 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

19. 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

20. 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.

21. 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 activity
SOURCE FORMS
• Needles ,pellets,Tubes
• Curie size cobalt unit- cathethron
• Encapsulated spheres in HDR brachytherapy.
• Teletherapy 1952 Canada by Johns

22. 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 .

23. IRIDIUM-192
USE
• 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.

24. IRIDIUM-192
HAIRPIN
• Used by Guide-Gutter Technique in smaller intraoral lesions
esp. small tumors of mobile portion of tongue,
FOM; Anal region
SEEDS
• Two types of seeds
1)Active dia 0.3 mm,
Length and outer dia 3mm and 0.5mm
2)Active dia 0.01mm
Iridium seeds encapsulated on nylon ribbon of
diameter of 0.8mm, spaced at 1-0.5cm center to
center distance

25. IRIDIUM-192
MINIATURE 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.

26. 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.

27. 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

28. 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

29. 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.

30. 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

31. 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.

32. 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 iodinateddeoxyuridine.
• Tried as seeds in LDR temporary implants

33. 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.

34. 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

35. 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

36. 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

37. 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.

38. RADIOISOTOPE IMAGING
organ Isotope used / activity
brain In-113m / 7-10mCi
kidney Hg-197 / 150mCi
lungs Tc-99 / 1mCi
I-131 / 0.15-0.3mCi
In-113 / 1mCi
spleen Cr-51 / 0.3mCi
bone Sr-85 / 0.1mCi
Sr-87 / 1mCi
F-18 / 1mCi
pancreas Se-75 / 0.2mCi
placenta Cr-51 / 0.05mCi
Tc-99 / 0.5-1mCi

40. METABOLISM USE
Isotope used/
activity
Labeled material &
technique
Interference
Fat metabolism I-131/ .025-.05mCi Triolium
orally
%of dose excreted
in feces over
several days
Gastrointestinal
blood loss
Cr-51/ .03-.04mCi RBC
I.V
Activity in feces
Iron metabolism Fe-59/.003-.01mCI Ferrric citrate Rate of
disappearance from
plasma is index of
erythropoiesis

41. THANK YOU