RADIOISOTOPES AND CLINICAL USES

RADIOISOTOPES AND CLINICAL USES

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 m ass number 4 less and atomic number 2 less , have 4 to 8 Mev energy. 88 Ra 226 → 86 Rn 222 + 2 He 4 + 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

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 15 P ---> 32 16 S+ 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 15 P ---> 30 14 Si + 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 27 Co ---> 60 28 Ni + 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 (67hrs) (6hrs) Tc 99m------------> Tc 99 + γ RADIOACTIVE SERIES Naturally occurring radioactive elements grouped into 3 series : Uranium , Actinium, Thorium. U 238 ---------------> Pb 206 4.51 x 10 9 yr U 235 ---------------> Pb 207 7.13 x 10 8 yr Th 232 --------------> Pb 208 1.39 x 10 10 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 t 1/2 >>>>>>>> daughter t 1/2 e.g. 88 Ra 226 _________________ 86 Rn 222 + 2 He 4 transient equilibrium: parent t 1/2 >> daughter t 1/2 e.g. Mo-99-----------> Tc 99m + -1 β

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 THERAPY DIAGNOSIS internal external in vitro in vivo systemic sources tele radio 14 C 3 H 125 I others 201 Tl 123 I 111 In 67 Ga 81 Rb- 81m Kr others ß + emitters for PET 18 F, 11 C, 13 N, 15 O 86 Y, 124 I 68 Ge- 68 Ga 82 Sr- 82 Rb 131 I, 90 Y 153 Sm, 186 Re 188 W- 188 Re 166 Ho, 177 Lu, others a -emitters: 225 Ac- 213 Bi 211 At, 223 Ra 149 Tb e - -emitters: 125 I sealed sources and applicators: 192 Ir, 60 Co, 137 Cs others seeds for brachytherapy : 103 Pd, 125 I microspheres 90 Sr - 90 Y, others 60 Co- Tele cobalt gamma knife 137 Cs - 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 should be easily screened

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 Rcm 2 /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 Rcm 2 /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 Rm 2 / mCi -h Conversion factor w.r.t to radium is 2.53 mCi of Cs 137 per mg of Ra 226 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 125 I 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- I 125 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 I 125 over gold 198 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 Rcm 2 / mCi -h Seeds tried in permanent implant. Under development TANTULUM-182 0.18 – 0.5 MeV 6.87 Rcm 2 / 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 /mm 3 Tenth value layer in lead 0.2 mm To improve dose distribution and shelf life compared to I 125 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

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 Cs 137 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 /mm 3 so highly miniaturized LDR source seeds and HDR sources possible. Less attenuation in tissue than I 125 and Pd 103 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

39. 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

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