Dosimetry

1. Dosimetry Ultrasound interaction with tissue Sanja Dolanski Babić March, 2010.

2. Dosimetry

3. What’s the difference between radiation and radioactivity? Radiation - the process of emitting energy as waves or particles, and the radiated energy Radioactivity - the property of radionuclides of spontaneously emitting ionizing radiation Sources of radiation – natural and artificial Dosimetry – assessment of radiation dose by measuring or calculating and assessment of biological damages

4. Types of ionizing radiation

5. The half-life is the time taken for half of the atoms of a radioactive substance to decay. [A]= Bq Bq = 27 x 10-12 Ci

6. Pie chart for background radiations Standard warning sign for a possible radioactive hazard

8. Basic principle of devices for detecting and measuring of radiation Basic detector Measuring effects of radiation Effective volume of detector Electrical: el.current or impulse Optical Calorimetric Chemical Biological Fragments of fission a, b- particles X, g - radiation gass liquid solid

9. 1. Devices for track visualisation of radioactive particles– radiographic track and Wilson cloud chamber Devices for detecting and measuring of radiation: 2. Counters (detectors)– Geiger counter, scintillation detector, semiconductor detector, gamma-camera etc. 3. Dosimeter is a small portable instrument for measuring and recording the total accumulated dose of ionizing radiation a person receives – such as a film badge, thermoluminescent or pocket dosimeter Radiation detectors are used in: nuclear physics, medicine, particle physics, astronomy and industry

10. Protection from radiation Radiographic film Diagnostics Radiotherapy 4.1 Slide 1

11. Ionization Chamber (1898. Marie Curie) • device used for two major purposes: detecting charged particles in the air (as in a smoke detector) and for detecting or measuring of ionizing radiation • - device measures the electric current generated when radiation ionizes the gas in the chamber and therefore makes it electrically conductive • electric currents are very • low: around 10-15 A • dosimetry in medicine measures very low doses X and radiation Principle of an ionization chamber

12. Simplified diagram of a smoke alarm

13. Geiger-Müller Counter - detects a single particle of ionizing radiation and produce an audible click for each GM tube – simply gas detector – higher voltage at the source of current – imediate “chain” ionization of the gas – electric current is 1010 times higherthan primary electric current – GM counter is used to detect usually alpha and beta radiation

14. Scintillation counter - measures ionizing radiation - sensor fluoresces when struck by ionizing radiation - a sensitive photomultiplier tube measures the light from crystal - sodium iodide scintillation counter detects gamma rays

15. Chest X ray examination That’s how it used to be...

16. EXPOSURE(X)– measure for ionization of the air mass of 1kg X = DQ/Dm [X]=C/kg 1 R = 2.58 x 10-4 C/kg - defined only for electromagnetic radiations which energies are smaller than 3 MeV

17. RADIATION ABSORBED DOSE (D)– measure of increasing internal energy (DU) in a mass of 1 kg tissue (DU) caused by absorption of ionizing radiations D = DU/Dm [D]=Gy=J/kg 1Gy = 100 rad - defined for all ionizing radiations - measuring of absorbed doses are not possible in living tissues

18. dose in sivert

19. - EQUIVALENT DOSE is calculated: Deq = D x H; H is radiation quality factor[Deq]= Sv ; 1 Sv = 100 rem

20. EFFECTIVE EQUIVALENT DOSE: Deq x f - each body part has its own weight factor, f

21. Radiation levels and their effects --- DOSE SPEED – radiation doses during 1sec - very important to biological damages

22. Radiation levels and their effects

23. X ray examination 0.02- 0.05 mSv 0.03 mSv

24. Chest X ray examination Marija Surić, Institut za medicinska istraživanja, Zagreb

25. Interactions between Ultrasound and Tissue

26. Diagnostic frequency range: 0,5 MHz - 20 MHz the time of puls: 0,2 - 2,0 ms intensity: 1 - 100 mW/cm2 - amplitudes of vibrating: do 10 nm Therapy frequency range : 0,8 MHz - 1 MHz - constant wave intensity : 100 - 1000mW/cm2 - amplitudes of vibrating: 10 - 25 nm Conditions of ultrasound scanning

27. Ultrasound waves • have the depth of penetration at the f=0,88 MHZ around 5 cm for muscle tissue, 10 cm for fat tissue and 0,3 cm for bone • have very low apsorbtion in fat tissues (use for diagnostic), higher in muscles and the highest in bones (use for therapy)

28. Ultrasound waves • The sideeffects in diagnostic usage almost do not exist because the pulses are short, intensities are low and frequencies are very high. • Scanning of small structures (embrio, eye) requires higher frequencies because of the better resolution. But higher frequencies mean fast changes in local pressure what presents risk for breaking of macromolecules. Intensity must be lower.

29. Ultrasound effects: 1. thermical 2. mechanical 3. appereance of caviation 4. chemical 5. biological

30. 1.Thermical effects – are used in therapy; thermical stress possible 2. Mechanical effects – bonds in macromolecules break when amplitude of the oscillation is higher than 10 nm and the change of local pressure is few atmospheres

31. 3. Cavitation – the appereance of air bubbles inside the tissue that is treated by ultrasound of high intensity - molecular bonds are breaking and free radicals are occuring 4. Chemical effects – breaking of chemical bonds and producing free radicals 5. Biological effects – ultrasound is fatal for bacteria, viruses and fungies