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Radioisotopes seminar

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Radioisotopes seminar

  1. 1. RADIOISOTOPES USED IN BRACHYTHERAPY Dr.Vijay Palwe Dr. Gaurav Bahl
  2. 2. Brachytherapy <ul><li>Definition: </li></ul><ul><li>“ Placement of sealed radioactive sources into or immediately adjacent to the target tissue is called as brachytherapy.” </li></ul>
  3. 3. History <ul><li>“ Actually Radiotherapy started in the form of Brachytherapy” </li></ul>1898 : Marie & Pierre Curie isolated Radium and work on Brachytherapy started.
  4. 4. 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
  5. 5. <ul><li>1950-60s : Advent of mega voltage type tele-therapy machines had provided treatment option with non-invasive procedure; EBRT treatment. </li></ul><ul><li>So, there was decline in progress of interstitial Brachytherapy. </li></ul>Brachytherapy was considered ‘lost art’. History
  6. 6. <ul><li>1964 : </li></ul><ul><li>Bernard Pierquin et al . used Ir192 after-loading interstitial implant. </li></ul><ul><li>1980-90s : </li></ul><ul><li>HDR after-loading , computer planning & optimization came in use. </li></ul>New possibilities in Interstitial Brachytherapy with advantages of HDR after-loading & computer optimization . History
  7. 7. <ul><li>According to dose rate </li></ul><ul><li>1) High dose rate (HDR)- </li></ul><ul><li>- > 12 Gy/Hr </li></ul><ul><li>(Usual dose rate of HDR Brachy.is 100-300 Gy/Hr ) </li></ul><ul><li>2) Medium dose rate (MDR) </li></ul><ul><li>- 2-12 Gy/Hr </li></ul><ul><li>3)Low dose rate (LDR) - </li></ul><ul><li>- 0.4 -2 Gy/Hr </li></ul><ul><li>4)Ultra low dose rate (ULDR)- </li></ul><ul><li>-0.01-0.3 Gy/Hr </li></ul>Types of Brachytherapy
  8. 8. SOME BASIC DEFINITIONS <ul><li>Radioactivity: No. of disintegrations per unit time (sec ,min, hrs.) expressed in curies </li></ul><ul><li>1 curie (ci)=3.7x10 10 disintegration /sec </li></ul><ul><li>1 Bequerel (Bq) =1 disintegration / sec. (S.I.unit) </li></ul><ul><li>Half life(T1/2 ): “The time required for a radioactive isotope to lose half of its original activity .” </li></ul><ul><li>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.” </li></ul>
  9. 9. <ul><li>Exposure Rate : Ionization equivalent of the kerma in air </li></ul><ul><li>Exposure Rate constant : Exposure rate in R/h at a point from a 1mCi point source </li></ul><ul><li>Formula: </li></ul><ul><li>l 2 </li></ul><ul><li>Γ δ = (dx/dt) </li></ul><ul><li>A </li></ul><ul><li>Dx/dt=exposure rate due to photon of energy greater than δ ,at a distance l from a point source of activity A. </li></ul><ul><li>Special Unit- Rm 2 h -1 Ci -1 </li></ul>
  10. 10. Properties of an IDEAL brachytherapy source (Godden,1988 ) <ul><li>Gamma ray energy high enough to avoid energy deposition in bone by photo-electric effect. </li></ul><ul><li>Low enough to minimize need for radiation protection. </li></ul><ul><li>(ideal 0.2-0.4MeV) </li></ul><ul><li>T1/2 such that correction for decay during Rx is minimal </li></ul><ul><li>Absent / easily screened charge particle emission </li></ul>
  11. 11. <ul><li>High specific activity eg. 192 Ir </li></ul><ul><li>No gaseous disintegration product eg. radon </li></ul><ul><li>Insoluble & non-toxic </li></ul><ul><li>Not in powder form eg. Radium sulphate </li></ul><ul><li>Can be made in different shapes eg. 192 Ir </li></ul><ul><li>Perm. Implants- t1/2 should be short </li></ul>
  12. 12. Types of Radioisotopes depending upon type of emission <ul><li>γ emitters : 226 Ra, 222 Rn, 60 Co , 137 Cs, 192 Ir, 198 Au, </li></ul><ul><li>125 I , 103 Pd, 169 Yb, 145 Sm, 241 Am. </li></ul><ul><li>β emitters : 32 P, 90 Sr , 90 Y, 106 Ru, 49 Va, 166 Ho, 144 Pr </li></ul><ul><li>neutron emitter : 252 Cf </li></ul>
  13. 13. ISOTOPES USED IN BRACHYTHERAPY can be embedded in <ul><li>Surface Applicator- placed directly on surface of tumor eg. Hard palate, skin, ocular </li></ul><ul><li>Intracavitory - inserted into specially designed apparatus that is placed into body cavity eg. Gynec.malign, nasopharynx </li></ul><ul><li>Intraluminal- Various organs with lumen </li></ul><ul><li>(Oesophagus, endobronchial, biliary etc.) </li></ul><ul><li>Interstitial- Directly through tissues encompassing tumor </li></ul><ul><li>Intravascular- coronaries, peripheral art. internal mammary etc. </li></ul>
  14. 14. Radioactive sources: Past, present and future ? Yb169, Yu169, I125, Pd103, Yb169 P32 P32, Sr/Y90 Ir192 -- Intra vascular --- Cardiac stents— Catheter based cardiac— Catheter based peripheral - Au198, Cs131 I125, Pd103 Au198 I125 , Pd103 Rn222 -- Permanent implant – Conventional dose-rate- Ultra low dose rate-- -- I125, Pd103,Yb169 Yb169, Ir192 Cs137 Ir192 Ir192 Ra226 --- --- Interstitial --- Non after loading - After loading-- HDR Am241,Ir192, Yb169 Yb169,Ir192, Co 60 Cs137 Ir192 Ra226 Co60 Intracavitory--- LDR HDR Future Current Traditional Application
  15. 15. Properties of radioactive sources Permanent Implant Seeds 1.48 0.013 17 day 0.020 Pd103 Palladium Permanent Implant Seeds 1.45 0.025 59.6 day 0.028 I125 Iodine HDR ICA Sphere 13.07 11 5.26 yrs 1.25 Co60 Cobalt LDR/HDR Seeds, Wires, ribbon 4.69 6 73.8 day 0.379 Ir192 Iridium LDR ICA & Interstitial Tubes Needle 3.28 6.5 30 yrs 0.662 Cs137 Cesium Perm. implant Temp. mould Gas 8.25 16 3.83 day 0.83 Rn222 Radon LDR ICA & Interstitial Tubes Needle 8.25 16 1626yrs 0.83* Ra226 Radium Clinical applicaion Source form Exposure rate constant HVL Pb (mm) T1/2 E (mev) Isotope Element
  16. 16. LDR Temp Interstitial Seeds 0.885 0.060 340 day 0.043 Sm145 Samarium LDR Perm. Imp Seeds 0.64 0.030 9.69 day 0.030 Cs131 Cesium High LET LDR ICA Tubes - - 2.65 day 2.4 n Cf252 Californium LDR Interstitial Seeds 1.80 0.48 32 day 0.093 Yb169 Ytterbium LDR ICA Tubes 0.12 0.12 432 yrs 0.060 Am241 Americanum Ocular Plaque - - 28.9 yrs 2.24 b Sr90-Y90 Sr / Y Permanent Implant Seeds 2.35 6 2.7 day 0.412 Au198 Gold Clinical applicaion Source form Exposure rate constant HVL Pb (mm) T1/2 E (mev) Isotope Element
  17. 17. RADIUM <ul><li>Earliest & once the most commonly used isotope </li></ul><ul><li>Naturally occuring </li></ul><ul><li>T ½ =1626 yrs </li></ul><ul><li>Disintegrates very slowly to hazardous radioactive gas Radon </li></ul><ul><li>At least 78 γ rays from Ra & its decay products of energy- ranging from 0.184 MeV - 2.45 MeV (avg.0.83Mev) </li></ul><ul><li>Some high energy β rays (max.3.26 Mev) </li></ul><ul><li>β filtration : 0.5 mm of Lead/ platinum </li></ul><ul><li>Has been widely used for intracavitary,interstitial & mould applications </li></ul><ul><li>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. ) </li></ul>
  18. 18. 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
  19. 19. Uranium Ra Rn RaA RaB RaC Pb α α α βγ βγ T 1/2 1620Yrs 3.83days 3.05min 26.8min 19.7min Stable Radium : provides constant source, replenishes decaying stock of Radon
  20. 20. Wall thickness: 0.5mm of Pt+Ir alloy 1mm of Pb to stop β Gold foil : 0.1 mm thick Cells : used for loading Physical characters of Ra 226 needles Outer case(Pt+10%Ir) Space forRa+filler mixture Eyelet hole cells
  21. 21. NOW OBSOLETE because <ul><li>Leak of radioactive salt/gas </li></ul><ul><li>High cost </li></ul><ul><li>Difficulty in Disposal </li></ul><ul><li>Better Radium substitute </li></ul><ul><li>Produces hazardous radioactive gas Radon </li></ul><ul><li>Specific activity low </li></ul><ul><li>Mixture of several intermediate radioactive products-dose calculation error can occur. </li></ul>
  22. 22. CESIUM 137: ( Cs 137 ) <ul><li>Recovered from fission products made in Nuclear Reactor </li></ul><ul><li>T1/2 : 30 yrs </li></ul><ul><li>Relatively cheaper, extraction simple, </li></ul><ul><li>Decay system : </li></ul><ul><li>55 137 Cs 137 56 Ba + 0 -1 e + γ </li></ul><ul><li>No gaseous decay product, safer than Ra </li></ul><ul><li>γ ray energy = 0.662 MeV </li></ul><ul><li>Beta filtration – 0.5 mm Pt or stainless steel </li></ul><ul><li>Available in tubes, needles, pellets. </li></ul><ul><li>Replaced Ra in t/t of gynaecologic cancers. </li></ul>Miniature cylindrical source
  23. 23. Miniature cylindrical source of CAESIUM 137: ( Cs 137 ) 5mm Active bead (1.1mm dia.) Stainless steel 1.8 Miniature cylindrical source
  24. 24. 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.
  25. 25. 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
  26. 26. IRIDIUM 192 ( 192 Ir) <ul><li>Produced in Nuclear reactors. </li></ul><ul><li>T1/2 = 73.8 days </li></ul><ul><li>Decays through β emission and electron capture to 192 Pt and 192 Osmium </li></ul><ul><li>Decay scheme: 192 I 192 Pt+ 0 -1 e+ γ </li></ul><ul><li>Emits 11 γ rays of energies ranging from 0.136 to 0.613 MeV </li></ul><ul><li>Effective γ rays energy is appr. 0.380 MeV </li></ul><ul><li>Emits β particles max energy 0.670 MeV </li></ul><ul><li>β filtration = 0.1mm of platinum </li></ul><ul><li>(Eliminated by stainless steel capsule) </li></ul><ul><li>HVT- 4.5mm of Lead (Pb) </li></ul><ul><li>Available in nylon strands or as platinum cladded wire. </li></ul>
  27. 27. PHYSICAL PROPERTIES OF 192 Ir seed <ul><li>Seeds are 3mm long & 0.5 mm in dia. </li></ul><ul><li>Internal diameter core of 30%Ir +70%Pt surrounded by 0.2 mm thick stainless wall </li></ul>
  28. 28. 192 Ir wire( coil form) Single Pin Hair Pin Physical forms of 192 Ir- Core dia 0.1mm 0..4mm Sheath thickness 0.1mm 0.4mm Overall 0.3mm 0.6mm Wire Hair pins
  29. 29. GOLD ( 198 Au) <ul><li>Produced in Nuclear reactor when 197 Au absorbs one neutron </li></ul><ul><li>Emits primarily Y rays </li></ul><ul><li>Energy 0.412 MeV (monoenergetic) </li></ul><ul><li>T 1/2 = 64.7 hrs ( 2.7 days) </li></ul><ul><li>Available in seeds and grain forms encased in Pt (0.1mm) filters β radiation. </li></ul><ul><li>Suitable for permanent implants ( Short half life) </li></ul><ul><li>Replaced Radon seeds in permanent implants </li></ul><ul><li>Protection problem easily solved ( Emit only 3Y rays in contrast to complex spectrum of Ra & also lower y energy) </li></ul><ul><li>Also prepared in colloidal form for t/t of ascitis due to intraperitoneal tumors. </li></ul>
  30. 30. IODINE( 125 I) <ul><li>Produced in Nuclear reactors </li></ul><ul><li>Used in permanent implants & can also be used in removable implants. </li></ul><ul><li>T 1/2 = 59.6 days </li></ul><ul><li>Y ray photon Energy = 0.274 MeV & 0.355 MeV </li></ul><ul><li>Decay scheme = electron capture </li></ul><ul><li>124 Xenon 125 I 125 Telleurium </li></ul><ul><li>Adv over Rn & Au –longer t1/2 </li></ul><ul><li>-convenient for storage </li></ul><ul><li>- low photon energy, less shielding . </li></ul><ul><li>But- dosimetry is much complex </li></ul><ul><li>& most T/t planning systems doesn’t take anisotropy </li></ul><ul><li>in account </li></ul>
  31. 31. Types of Iodine 125 implants <ul><li>Type 6702 : used in temporary interstitial implants </li></ul><ul><li>Consists of welded Titanium capsule containing 3 resin spheres onto which 125 I is adsorbed by ion exchange. </li></ul><ul><li>Sources available in air kerma rate at 1 m of 6.4-51.9 μ Gy h -1 </li></ul><ul><li>Effective energy 28.5 kev </li></ul>125 I adsorbed on ion exchange resin 0.05 mm Titanium 0.8mm 4.5mm
  32. 32. Type 6711 <ul><li>Used in permanent implant </li></ul><ul><li>Consists of welded titanium capsule containing I 125adsorbed onto a silver rod (which also act as x ray marker) </li></ul><ul><li>Active length=3mm & dia. 0.5 mm </li></ul><ul><li>Overall length = 4.5mm & dia.0.8mm </li></ul><ul><li>Sources available with air kerma rate of 1m of 0.13-7.58 μ Gy h -1 </li></ul>0.8mm 0.5mm 3.0mm 4.5mm
  33. 33. Model 2300 of 125 I <ul><li>Radioactive Iodine adsorbed on a tungston wire that is encapsulated by 2 walls of titanium </li></ul><ul><li>Suitable for both temporary & permanent implantations as available in wide range of source strengths. </li></ul><ul><li>Tungston wire – radiographic marker </li></ul><ul><li>Double walled encapsulation –reduces risk of radioactive leakage </li></ul>
  34. 34. PALLADIUM 103 ( 103 Pd) <ul><li>Produced in nuclear reactors when stable 102 Pd absorbs a neutron. </li></ul><ul><li>Decay scheme = via electron capture ( 1 st & 2 nd excited states of Ruthenium103) </li></ul><ul><li>T1/2 = 17 days </li></ul><ul><li>Photon energy = 21 kev </li></ul><ul><li>Useful in permanent implants </li></ul><ul><li>HVL for Lead= 0.008 mm </li></ul><ul><li>Substitute for 125 I ( shorter half life ) </li></ul><ul><li>Available in form of seeds </li></ul><ul><li>Used in prostate implants </li></ul>
  35. 35. Titanium end cup Lead Xray marker Pd plated grafite pellet Laser weld 103Pd seed 0.8mm 4.5mm
  36. 36. COBALT 60 ( 60 Co) <ul><li>Produced by neutron activation of stable isotope 59 Co </li></ul><ul><li>Decay scheme: 60 27 Co 60 28 Ni+ -1 0 e + y </li></ul><ul><li>T1/2 = 5.26 yrs </li></ul><ul><li>Each disintegration produces 2 y rays of energy 1.33 & 1.17 MeV (avg energy 1.25 MeV ) </li></ul><ul><li>β energy= 0.318 MeV </li></ul><ul><li>HVL in Lead = 10 mm </li></ul><ul><li>Relatively high penetrating power makes an excellent isotope in teletherapy. </li></ul><ul><li>Recently used in opthalmic plaques for t/t of ocular melanomas & retinoblastomas. </li></ul><ul><li>Activity higher , can be used in brachytherapy. </li></ul>
  37. 37. Reasons for re-emergence of 60Co as brachytherapy source <ul><li>No need for frequent replacements </li></ul><ul><li>Cost effective </li></ul><ul><li>Miniaturised,(same size of conventional Ir192 source) </li></ul><ul><li>High activity </li></ul><ul><li>Low operating cost. </li></ul>
  38. 38. STRONTIUM 90 ( 90 Sr) & Yttrium90 ( 90 Y) <ul><li>90 Sr decays through β ray emission to 90 Y </li></ul><ul><li>90 Sr always coexist in equilibrium with radioactive daughter 90 Yttrium </li></ul><ul><li>T1/2=28 yrs </li></ul><ul><li>Max β ray energy =0.54 MeV </li></ul><ul><li>Dose falls very rapidly away from the applicator & is appr.20% at 2mm depth in tissue. </li></ul><ul><li>Dose rate on surface in range of 100 cGy /S thus t/t delivered in seconds </li></ul><ul><li>Used in corneal ulcers, pterygium, corneal vascularization & neoplasms. </li></ul><ul><li>Yttrium in colloidal preparations used in malignant effusions. </li></ul><ul><li>Yttrium pellets in pituitary gland to abolish its secretary activity in hormonal control of breast cancers. </li></ul><ul><li>Yttrium used in SIR (selective internal radiation) in liver malignancies. </li></ul><ul><li>89 Sr (non-sealed) used in t/t of bone mets. </li></ul>
  39. 39. PHOPHORUS 32 ( 32 P) <ul><li>Unsealed radioisotope </li></ul><ul><li>Produced in nuclear reactor by neutron bombardment of sulfur, </li></ul><ul><li>Pure β -emitter </li></ul><ul><li>Max β energy =1.71 MeV </li></ul><ul><li>T1/2 =14.7 days </li></ul><ul><li>Formerly used in t/t of polycythemia vera & other hemat. malignancies </li></ul><ul><li>Also in t/t of superficial warts, basal cell ca, angiomas. </li></ul><ul><li>Now used in intrapleural, intraperitonial instillations. </li></ul><ul><li>32 P coated stents - used in t/t of arterial restenosis. </li></ul>
  40. 40. CALIFORNIUM 252 ( 252 Cf) <ul><li>Neutron emitter (Radiobiological superiority) </li></ul><ul><li>Production from multiple neutron capture by 238 U </li></ul><ul><li>Decay scheme – alfa emission </li></ul><ul><li>Produces charged particles, gamma rays & neutrons </li></ul><ul><li>T1/2=2.63 yrs </li></ul><ul><li>Neutron energy= 2.3 MeV </li></ul><ul><li>Typical source -0.25ug – 0.45ug (each ug emits 2.34 x10 6 neutrons) </li></ul><ul><li>Available in seeds or tubes form </li></ul><ul><li>Used in ca cervix LDR ICA </li></ul>
  41. 41. NEWER ISOTOPES IN BRACHYTHERAPY
  42. 42. RUTHENIUM 106 ( 106 Ru) <ul><li>Fission by-product </li></ul><ul><li>Decay scheme- β emission </li></ul><ul><li>Max energy -0.039 MeV, avg.energy-0.009 MeV </li></ul><ul><li>106 Ru 106 Rh + β </li></ul><ul><li>T1/2=368 days </li></ul><ul><li>106 Ru in radioactive equilibrium with daughter 106 Rh </li></ul><ul><li>Used in shallow opthalmic lesions </li></ul>
  43. 43. VANADIUM 49( 49 Va) <ul><li>Produced through (p,n) reaction with 48 Ti </li></ul><ul><li>Emits positrons & gamma rays </li></ul><ul><li>Positrons avg energy -0.696MeV , y ray avg energy- 0.511 MeV </li></ul><ul><li>T1/2= 16 days </li></ul><ul><li>Stent being utilized for intracoronary applications </li></ul>
  44. 44. HOLMIUM166 ( 166 HO) <ul><li>Produced through (n,y) reaction with 165 Ho </li></ul><ul><li>Decay scheme- β emission </li></ul><ul><li>166 Ho 165 Ho+ β 166 Er( stable ) </li></ul><ul><li>Max β energy= 1.9 MeV (avg 0.63) </li></ul><ul><li>T1/2=27 hrs </li></ul><ul><li>Considered for intravascular brachytherapy </li></ul>
  45. 45. PRASEODYMUM 144 ( 144 Pr) <ul><li>Fission byproduct of Cerium144 </li></ul><ul><li>Decay scheme – β emission </li></ul><ul><li>T1/2 =285 days </li></ul><ul><li>144 Pr 144 Ni+ β </li></ul><ul><li>Max β energy 3 MeV (avg 1MeV) </li></ul><ul><li>Considered for intravascular brachytherapy. </li></ul>
  46. 46. THANK YOU

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