Department of Oral Health and Medicine, University Center for Dental Medicine Basel, University of Basel, Basel, Switzerland.
Division of Radiological Physics, Department of Radiology, University of Basel, Basel, Switzerland.
Dentomaxillofac Radiol. 2022 Sep 1;51(6):20210316. doi: 10.1259/dmfr.20210316. Epub 2022 Jun 28.
To investigate the effect of two different large field of view (FOV) positions in the vertical dimension and shielding (thyroid collar and eyeglasses) on the effective dose and the local doses of various sites of the craniofacial complex.
Organ doses and effective doses were calculated based on the measured doses using 27 pairs of thermoluminescent dosemeters in a paediatric tissue-equivalent of a 10-year-old anthropomorphic phantom. The large FOV of the 3D Accuitomo F170 CBCT scanner was used to image parts of the craniofacial complex. Six protocols were performed: (A) cranial position without shielding; (B) cranial position with shielding; (C) caudal position without shielding; (D) caudal position with shielding, (E) similar to C with 360 rotation and (F) similar to D with 360° rotation. Measurements were obtained in duplicate, and the relative δ value (%) was applied to compare the average doses between the protocols.
Changing the FOV position from cranial to caudal without using shielding resulted in an increase of the effective dose of 18.8%. Use of shielding in the caudal position reduced the dose by 31.6%. Local absorbed dose of the thyroid had the most relevant impact on calculation of the effective dose, followed by oesophagus, bone marrow and bone surfaces, especially when comparing the different protocols.
Application of shielding devices for thyroid in combination with a most caudal positioning of FOV led to the lowest local absorbed doses as well as the effective dose in a child phantom model.
研究垂直方向上两种不同大视野（FOV）位置和屏蔽（甲状腺领和眼镜）对颅面复合体各部位有效剂量和局部剂量的影响。
使用 27 对热释光剂量计在 10 岁儿童人体等效模型的组织等效体模中测量剂量，基于测量剂量计算器官剂量和有效剂量。3D Accuitomo F170 CBCT 扫描仪的大 FOV 用于对颅面复合体的部分部位进行成像。共进行了 6 种方案：（A）无屏蔽的颅位；（B）有屏蔽的颅位；（C）无屏蔽的尾位；（D）有屏蔽的尾位，（E）类似 C 方案的 360°旋转和（F）类似 D 方案的 360°旋转。进行了两次测量，应用相对 δ 值（%）比较各方案的平均剂量。
不使用屏蔽从颅位改为尾位时，有效剂量增加了 18.8%。尾位使用屏蔽可使剂量降低 31.6%。甲状腺的局部吸收剂量对有效剂量的计算影响最大，其次是食管、骨髓和骨表面，尤其是在比较不同方案时。
在儿童体模模型中，应用甲状腺屏蔽装置并结合最尾位的 FOV 定位，可使局部吸收剂量和有效剂量达到最低。
