Quintero-Quintero A, Patiño-Camargo G, Soriano Á, Palma J D, Vilar-Palop J, Pujades M C, Llorca-Domaica N, Ballester F, Vijande J, Candela-Juan C
Department of Atomic, Molecular and Nuclear Physics, Universitat de València (UV), Burjassot (València) 46100, Spain. Grupo de Física Nuclear Aplicada y Simulación, Universidad Pedagógica y Tecnológica de Colombia (UPTC), Tunja (Boyacá), 150003, Colombia.
J Radiol Prot. 2018 Jun;38(2):549-564. doi: 10.1088/1361-6498/aab38f. Epub 2018 Mar 2.
Fluoroscopy guided interventional procedures provide remarkable benefits to patients. However, medical staff working near the scattered radiation field may be exposed to high cumulative equivalent doses, thus requiring shielding devices such as lead aprons and thyroid collars. In this situation, it remains an acceptable practice to derive equivalent doses to the eye lenses or other unprotected soft tissues with a dosimeter placed above these protective devices. Nevertheless, the radiation backscattered by the lead shield differs from that generated during dosimeter calibration with a water phantom. In this study, a passive 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 H (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 0° and 60°, and lead thicknesses between the TLD and phantom of 0.25 and 0.5 mm Pb were considered. 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 0°). The corrected dose algorithm was validated in laboratory conditions with dosimeters irradiated over a thyroid collar and angular incidences of 0°, 40° and 60°, as well as with dosimeters worn by interventional radiologists and cardiologists. The corrected dose algorithm provides a better approach to estimate the equivalent dose to unprotected soft tissues such as 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.
荧光透视引导介入手术给患者带来显著益处。然而，在散射辐射场附近工作的医护人员可能会受到高累积当量剂量照射，因此需要铅围裙和甲状腺防护颈圈等屏蔽装置。在这种情况下，将剂量计置于这些防护装置上方来推算眼晶状体或其他未受保护软组织的当量剂量仍是一种可接受的做法。不过，铅屏蔽产生的反向散射辐射与剂量计在水模体中校准期间产生的辐射不同。在本研究中，利用蒙特卡罗（MC）代码Penelope对被动式个人热释光剂量计（TLD）进行建模。将所得结果与在二级标准剂量测定实验室参考条件下进行的测量结果进行验证。接下来，使用MC模型评估剂量计佩戴在铅屏蔽上方时估算未受保护软组织的个人当量剂量H(0.07)所需的反向散射校正因子。为此，用代表患者散射的荧光透视束结果的光子束在水板模体上照射TLD。考虑了0°和60°的入射束角度以及TLD与模体之间0.25和0.5毫米铅的铅厚度。将结果与参考条件下（即无铅屏蔽且入射角为0°）的结果比较，计算出反向散射校正因子为1.23（与铅厚度无关）。校正剂量算法在实验室条件下得到验证，剂量计在甲状腺防护颈圈上照射且入射角为0°、40°和60°，以及介入放射科医生和心脏病专家佩戴剂量计的情况。校正剂量算法为估算眼晶状体等未受保护软组织的当量剂量提供了更好的方法。未屏蔽反向散射辐射的剂量计在佩戴于铅围裙上方时可能会低估个人当量剂量，因此应为此目的进行专门表征。
