For MBBS, BDS and MD students

1. RADIOISOTOPES IN
MEDICINE
Prof (Dr) Viyatprajna Acharya
M.D. PhD

2. At the end of the class….
• You’ll learn the background of use of radioisotopes in Medicine
• Terminologies in relation to radioisotopes
• Uses of radioisotope in research
• Diagnostic applications
• Therapeutic applications

3. Earnest Rutherford (N.P. 1908)
• Nuclear theory of atom
• Negatively charged
electrons revolve around
positively charged nucleus
• Niels Bohr (N.P. 1922)-
Modified Rutherford theory

4. Two times Nobel prize winner(Phy-
1903, Chem-1911)
• Coined the term “Radioactivity”
• Won prize in Physics for radioactivity
• Won NP in Chemistry for discovering
Radium and Polonium
• 1st woman to win NP
• 1st woman to win NP twice
• 1st woman professor at Sorbonne
University
• 1st woman/man scientist to win NP twice
in 2 different subjects
• Died of aplastic anemia due to prolonged
exposure of Radium
• Daughter Irene and Son-in-law E. Joliot
got NP for artificial production of
isotopes and Polonium

5. Why study radioisotopes??
•Research
•Diagnosis & Prognosis
•Treatment

6. Radioactivity
• It is the spontaneous emission of accelerated high energy
particles and electromagnetic radiations from the unstable
atomic nuclei of an element.
• The nucleus thereby loses energy and changes into more stable
nucleus of another element.

7. Few terminologies…..
• Proton (p+)- one +ve charge; 4.8x 10-10 esu
very long T1/2- ~1015 years
• Electron (e-)- -ve ly charged- -4.8x 10-10 esu
Mass is 1/2000 of proton
• Neutron- No charge; Mass equals to proton
• Isotope- Same atomic number, different atomic mass
e.g. I125, I 131
• Isobar- Same atomic mass, different atomic number e.g. C14,
N14
• Different types of radiation
 γ rays- Electromagnetic radiations
α & β- high-velocity charged particles

8. Radioactive decay is a first order process

9. Half-life of radioactivity
• Time taken for an isotope to become half of its radioactivity
• T1/2 of I131 is 8 days

10. Units of radioactivity
• Curie- most frequently used unit
• Becquerel- SI derived unit of radioactivity
• Specific activity- activity per quantity of a radionuclide and is a physical
property of that radionuclide
• Roentgen- measurement of exposure dose
• Rad and gray- Absorbed dose by tissue; maxm 5rads/year allowable limit
• Rem- Roentgen equivalent of man; unit of radiation dosage

11. Applications of radioactivity in research
• Tracers in metabolic pathways e.g. C14, N15 label, β emitters
• Turnover rate of a substance in the body
• Total body content of a particular substance can be known– Isotope
dilution technique e.g. Uric acid pool, ECF, ICF
• Carbon dating- Paleobiology

13. • 32P- Trace the nucleic acid synthesis in vivo and in vitro
• 51Cr- RBC lysis
Immunological or pathological mechanisms
• Double-labelled water molecules for BMR detection

14. Diagnostic application of radioisotopes
• 51Cr- Internal haemorrhage and intravascular hemolysis
• Thyroid uptake studies- 15μCi I131 administered
Normal– Within 2hrs- 25% uptake
Within 24hrs- 50% uptake
Hyperthyroidism- ↑uptake
Hypothyroidism- ↓uptake
• Thyroid scanning- Few hrs after administering I131, patient is put
under thyroid scanner (gamma ray counter)
Silent nodule- Thyroid CA
Cold nodule- non-functioning tissue- 20% are malignant, goiter, cyst,
fibrosis
Hot nodule- Over-Functioning tissues- Thyroiditis, adenoma

15. • Bone scan- 90Sr
• Kidney scanning- 131I labelled Hippuran
131I labelled Diodrast
• 99mTc, 137Ba- Radiocardiography- Nuclear stethoscope
• 133Xe- study cerebral circulation
• PET Scan- 11C, 13N, 15O

16. Diagnostics related to Biochemistry
• RIA
• Radiochromatography
• Autoradiography
• Radioimmunoelectrophoresis

17. • Acts on dividing cells
• Cancer therapy and few non-malignant cases
• Brachytherapy- 137Cs needles, Ra needles in Uterine CA, CA Cx, Buccal CA
• Teletherapy- Liquid form cancers usually, CA Cx, vagina, vulva;
Deep X-ray was used earlier- now obsolete
Linear accelerator (LINAC)- Electrons are accelerated to higher energy
levels of 8-12 MV and directed to CA tissue
131I – thyroid CA
32P- Polycythemia vera
Therapeutic applications of radioisotopes

18. Biological effects of radioactivity
A. Stochastic (zero-threshold effects)- Genetic effects, malignancies
B. Non-stochastic (dose can be decided)-
• DNA damage
• Free radical damage
• Local necrosis
• Exposure from Medical imaging has doubled in USA from 1980 to today
• CT Scan alone accounts for 24% of radiation exposure
• Repeat CT scans increase risk of cancer

19. Effects on normal tissues
Skin- Epilation, sweat glands permanently damaged
erythema, blisters– Acute radiodermatitis
Chronic radiodermatitis- Skin atrophy, hypopigmentation,
fibrosis, lack of elasticity
Overdose- burning of skin, sloughing
GIT- Nausea vomiting
Chronic- adhesions, obstruction
Blood cells- Pancytopenia
Reproductive organs- 1000 rad- sterility

20. Radiation protection
• Lead apron
• Dosimeter- measures radiation
exposure over a certain period
of time

21. It is the darkest before dawn
www.vpacharya.com