Room: Exhibit Hall | Forum 1
Purpose: To study the effect of a lead shield in the calibration of a dosimeter placed above the shield in a fluoroscopy guided interventional procedure using MC simulations, and to derive a backscatter correction factor and a new dose calculation algorithm that allows estimating Hp (0.07) to unprotected soft tissues.
Methods: A personal thermoluminescent dosimeter (TLD) was modelled by means of the Monte Carlo (MC) code Penelope. The results obtained were validated against measurements performed in reference conditions in a secondary standard dosimetry laboratory. Next, the MC model was used to evaluate the backscatter correction factor needed for the case where the dosimeter is worn over a lead shield to estimate the personal equivalent dose Hp (0.07) to unprotected soft tissues. For this purpose, the TLD was irradiated over a water slab phantom with a photon beam representative of the result of a fluoroscopy beam scattered by a patient. Incident beam angles of 0Â° and 60Â°, and lead thicknesses between the TLD and phantom of 0.25 and 0.5 mm Pb were considere.
Results: A backscatter correction factor of 1.23 (independent of lead thickness) was calculated comparing the results with those faced in reference conditions (i.e., without lead shield and with an angular incidence of 0Â°). The corrected dose algorithm was validated in laboratory conditions with dosimeters irradiated over a thyroid collar and angular incidences of 0Â°, 40Â° and 60Â°, as well as with dosimeters worn by interventional radiologists and cardiologists.
Conclusion: The corrected dose algorithm provides a better approach to estimate the equivalent dose to unprotected soft tissues such as the eye lenses. Dosimeters that are not shielded from backscatter radiation might underestimate personal equivalent doses when worn over a lead apron and, therefore, should be specifically characterized for this purpose.
Not Applicable / None Entered.