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RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology. RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY. Part 16.1: Optimization of protection in fluoroscopy Practical exercise. Overview.

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RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

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  1. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION INDIAGNOSTIC ANDINTERVENTIONAL RADIOLOGY Part 16.1: Optimization of protection in fluoroscopy Practical exercise

  2. Overview • To become familiar with quality control tests in fluoroscopy. • To measure the standard entrance dose rate to the patient • To assess the patient thickness variation effect on scattered radiation 16.1: Optimization of protection in fluoroscopy

  3. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 16.1: Optimization of protection in fluoroscopy Measurement of standard entrance dose rate

  4. Fluoroscopy - Standard Dose Rate Purpose : • Measurement of dose rate at the entrance of patient for different thickness • Effect on scattered radiation Method : • Use different water equivalent absorber (acrylic, 20 cm for a standard patient) or copper sheets (2 mm for a standard patient • Place dosimeter on input (x-ray tube side) of absorber 16.1: Optimization of protection in fluoroscopy

  5. Set-up for measurement of standard dose rate. 16.2: Optimization of protection in fluoroscopy

  6. The ionization chamber should be protected pressure and possible malfunctioning. It should be in contact with the acrylic to include backscatter in the measurement. 16.2: Optimization of protection in fluoroscopy

  7. Use10 cmthickness of acrylic to simulate a thin patient. The table to intensifier distance is35 cm(this distance will be kept constant for the different patient thicknesses) 16.1: Optimization of protection in fluoroscopy

  8. The chamber is easily centred using the fluoroscopic image 16.1: Optimization of protection in fluoroscopy

  9. The entrance dose rate is1.78 mGy/min. 16.1: Optimization of protection in fluoroscopy

  10. The phantom thickness is now20 cm. 16.1: Optimization of protection in fluoroscopy

  11. The chamber now reads8.85 mGy/min. 16.1: Optimization of protection in fluoroscopy

  12. If the distance between the input screen of the intensifier and the entrance of the patient is increased, i.e.,extra 20 cm. The patient entrance dose rate will increase. 16.1: Optimization of protection in fluoroscopy

  13. Note:the chamber looks magnified (the intensifier is further away from the patient). 16.1: Optimization of protection in fluoroscopy

  14. Before(intensifier-table distance: 35 cm) Now(intensifier-table distance: 55 cm) 16.1: Optimization of protection in fluoroscopy

  15. The entrance dose rate with the intensifier at 55 cm from the table is17.9 mGy/min(to be compared with the previous value of 8.85 mGy/min). 16.1: Optimization of protection in fluoroscopy

  16. Now the phantom thickness is increased up to30 cmof acrylic. 16.1: Optimization of protection in fluoroscopy

  17. The patient entrance dose rate at the surface of the phantom increases to 24.8 mGy/min(the reading was 8.85 with 20 cm thickness). 16.1: Optimization of protection in fluoroscopy

  18. The dose rate due to scatter radiation also increases with the patient thickness. For30 cmacrylic, 3 mGy/his measured close to the phantom. 16.1: Optimization of protection in fluoroscopy

  19. With thehigh contrast modethe dose rate for scatter radiation (30 cm acrylic), increases to 7 mGy/h.The patient entrance dose rate is now 59.6 mGy/min. 16.1: Optimization of protection in fluoroscopy

  20. With10 cmacrylic the dose rate due to scattered radiation is 0.2 mGy/h. 16.1: Optimization of protection in fluoroscopy

  21. With20 cmacrylic the dose rate due to scattered radiation is 1 mGy/h. 16.1: Optimization of protection in fluoroscopy

  22. With30 cmacrylicthe dose rate due to scattered radiation is 3 mGy/h. 16.1: Optimization of protection in fluoroscopy

  23. Note that with the extra thickness the image quality is extremely poor (the border of the chamber is hardly visible) 16.1: Optimization of protection in fluoroscopy

  24. Fluoroscopy - Standard Dose Rate Analysis : • should be < 25 mGy/min Frequency : • acceptance, tube change • generator repair • intensifier repair • 6 monthly 16.1: Optimization of protection in fluoroscopy

  25. Where to Get More Information Quality Control in Diagnostic Imaging, Gray JE, Winkler NT, Stears J, Frank ED. Available at no cost. http://www.diquad.com/QC%20Book.html 15.3: Optimization of protection in radiography

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