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Radiation protection in NM

Radiation protection in NM. Dr.Sayed abbas NMT 244 Lecture 3. Overview. Key issue in use of unsealed radioactive sources _ External hazard _ Contamination _ Internal hazard. Sealed/ Unsealed Sealed source Radioactive material sealed / encapsulated and cannot escape .

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Radiation protection in NM

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  1. Radiation protection in NM Dr.SayedabbasNMT 244Lecture 3

  2. Overview • Key issue in use of unsealed radioactive sources _ External hazard _ Contamination _ Internal hazard

  3. Sealed/ Unsealed • Sealed source • Radioactive material sealed / encapsulated and cannot escape . • Unsealed source • Material can escape .

  4. What is a Sealed Radioactive Source? A sealed radioactive source is a container of encapsulated radioactive material, which usually has the appearance of a small, harmless piece of metal. The capsule or material of a sealed source is strong enough to maintain leak tightness under the conditions of use for which the source was designed,

  5. Who is exposed?

  6. Nature of exposure

  7. General Concepts: • ALARA “Radiation exposures should be kept (As Low As Reasonably Achievable)” • Methods & Techniques that reduce patient exposure also reduce exposure for the radiological technologist and other occupationally exposed persons. The following are the most technique used: • Beam Limitation Devices. • Protective lead aprons & shielded barriers function as gonadal shields for diagnostic radiology personnel. • Optimum Exposure Factors. • Use high speed image receptor System. • Employment of proper radiographic technique

  8. External Hazard • Must protect against External Radiation • _ Time • _ Distance • _ Shielding

  9. Basic principles • Protection against exposure from external radiation hazard is achieved through the application of three principles: 1. Decrease the exposure time. 2. Increase the distance from the radiation source. 3. Use shielding where necessary. Time: • The dose accumulated by a worker in an area having a particular dose rate is proportional to the time spent in that area: • Total doses can be reduced by minimizing the time spent in a radioactive area. Dose = Dose rate  Exposure time

  10. Time • Handle for as short a time as possible : Seems obvious , but several techniques will help • Can use ‘Butterflies’ / cannulas for injections • ( After loading used in Brachytherapy)  radioactive implants directly into the tissue.

  11. Distance • Keep as far away from source as possible : • seems obvious , but several techniques will help • Use forceps to handle sources • Use long-handled carriers to transport sources • Firms use large Type A packages • Radioactive patients sit apart from family • Plan departments to maximize distances

  12. Distance: • Distance is the most effective means of protection from ionizing radiation. Radiological technologist receives less radiation exposure by standing farther away from a source of radiation . Inverse Square Law : • It expresses the relationship between the distance and intensity of radiation . • The law states: the intensity of the radiation is inversely proportional to the square of the distance .this means that as the distance between the radiation source and measurement point increases , the quantity of radiation measured at that point decreases by the square of its distance from the source .

  13. Inverse square law

  14. I1 / I2 = (d2)2 / (d1)2 • In the case of a point source, the variation of dose rate with distance is given simply by the inverse square law. where I1 and I2 are the intensity or dose at distance d1 and d2 respectively. • Doubling the distance from the sourcereduces the dose rate to one quarter of its original value. How much does trebling the distance from the source reduce the dose rate? Example: the dose rate at 2m from a particular gamma source is 400 sv/h. What distance will it give a dose rate of 25 Sv/h? • Solution:I1 / I2 = (d2)2 / (d1)2 400*2 = 25 * (d2)2 (d2)2 = 64 d2= 8m

  15. Shielding • Need to Know type of radiation • Imaging uses Y radiation • Radiochemical Labs mostly B radiation • Plan to use local shielding • May also need Wall shielding

  16. Local shielding 1 • Vial shielding • β emitters –Perspex Vial shields & storage • Glass vial fine <0.75MeV • Lead>0.7mm attenuation outweighs Bremsstrahlung • ϒemmitters –Tungsten Vial shields & lead- lined box for storage • Tc-99m generators use Depleted Uranium • ( increased proportion of U-238)

  17. Local Shielding 2 • Nuclear Medicine Syringes • ϒemitters – Tungsten syringe shields lead-lined box for storage

  18. Local Shielding 3 • L- Bench Shielding • ϒ emitters - lead-lined shield & lead- glass • Β emitters - Perspex L shields

  19. Local Shielding 4 • Radioactive Waste Shielding • ϒemitters – Sharps bins & lead-lined containers • β emitters – Perspex waste containers, often lined with polythene bags

  20. Sharps bins & lead-lined containers ϒ emitters

  21. Wall shielding • Often unnecessary for Nuclear Medicine • However, same principles employed for X-ray rooms should be applied to assess requirements for Nuclear Medicine ( or Radiochemical laboratories)

  22. Example: PET • Positron Emission Tomography • 511keV Gammas • 370MBq activities • Short half-lives • High energy gamma photons so shielding must be thicker • Higher doserates lead to operational difficulties

  23. PET facilities • Pharmaceutical lab • Cyclotron, synthesis, dispensing & QA • Greater level of work than standard nuclear medicine • Patient prep & scanning • _ Admin, injection, patient rest, scan ,discharge • _patient poses greater hazard due to PET energy and activity

  24. PET Pharmaceutical Production • Cyclotron heavily shielded in concrete • Inside large shielded vault • Air extraction & monitoring • No entry to vault during production

  25. PET lab • Cyclotron products transferred by underground lines into lab hot cells • Initial synthesis by equipment inside shielding

  26. PET Lab • Subsequent dispensing in shielded cabinet • Automated syringe fill station • Lead shielding around hot objects • QA carried out in laminar flow cabinet using lead ‘’ castles’’

  27. Patient preparation • All questions , admin, instructions & chatting BEFORE presence of activity • Injection using butterfly • Syringe stored in thick lead pot _special base to prevent abandonment • Issue of syringe shield use: better or worse dose levels? • _High energy gamma photons

  28. Scanning • Patient rested in isolated room_Watched on CCTV , call button • Lines on floor to WC & scanner • Staff encourage self-positioning • Controls in shielded room

  29. Thank You for your kind attention

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