Pattern Recognition Lab, FAU Erlangen-Nürnberg, Erlangen, Germany.
Erlangen Graduate School in Advanced Optical Technologies (SAOT), Erlangen, Germany.
Int J Comput Assist Radiol Surg. 2019 Nov;14(11):1859-1869. doi: 10.1007/s11548-019-02037-6. Epub 2019 Aug 3.
With X-ray radiation protection and dose management constantly gaining interest in interventional radiology, novel procedures often undergo prospective dose studies using anthropomorphic phantoms to determine expected reference organ-equivalent dose values. Due to inherent uncertainties, such as impact of exact patient positioning, generalized geometry of the phantoms, limited dosimeter positioning options, and composition of tissue-equivalent materials, these dose values might not allow for patient-specific risk assessment. Therefore, first the aim of this study is to quantify the influence of these parameters on local X-ray dose to evaluate their relevance in the assessment of patient-specific organ doses. Second, this knowledge further enables validating a simulation approach, which allows employing physiological material models and patient-specific geometries.
Phantom dosimetry experiments using MOSFET dosimeters were conducted reproducing imaging scenarios in prostatic arterial embolization (PAE). Associated organ-equivalent dose of prostate, bladder, colon, and skin was determined. Dose deviation induced by possible small displacements of the patient was reproduced by moving the X-ray source. Dose deviation induced by geometric and material differences was investigated by analyzing two different commonly used phantoms. We reconstructed the experiments using Monte Carlo (MC) simulations, a reference male geometry, and different material properties to validate simulations and experiments against each other.
Overall, MC-simulated organ dose values are in accordance with the measured ones for the majority of cases. Marginal displacements of X-ray source relative to the phantoms lead to deviations of 6-135% in organ dose values, while skin dose remains relatively constant. Regarding the impact of phantom material composition, underestimation of internal organ dose values by 12-20% is prevalent in all simulated phantoms. Skin dose, however, can be estimated with low deviation of 1-8% at least for two materials.
Prospective reference dose studies might not extend to precise patient-specific dose assessment. Therefore, online organ dose assessment tools, based on advanced patient modeling and MC methods, are desirable.
随着介入放射学中对 X 射线辐射防护和剂量管理的兴趣不断增加，通常会使用人体模型对新程序进行前瞻性剂量研究，以确定预期的参考器官当量剂量值。由于存在不确定性，例如患者精确定位的影响、模型的通用几何形状、有限的剂量计定位选项以及组织等效材料的组成，这些剂量值可能无法进行患者特定风险评估。因此，本研究的目的首先是量化这些参数对局部 X 射线剂量的影响，以评估它们在评估患者特定器官剂量中的相关性。其次，这方面的知识进一步验证了一种模拟方法，该方法可以使用生理材料模型和患者特定的几何形状。
使用 MOSFET 剂量计进行了人体模型剂量测定实验，以复制前列腺动脉栓塞 (PAE) 中的成像场景。确定了前列腺、膀胱、结肠和皮肤的器官当量剂量。通过移动 X 射线源来再现可能导致患者小位移的剂量偏差。通过分析两种常用的模型来研究几何形状和材料差异引起的剂量偏差。我们使用蒙特卡罗 (MC) 模拟、参考男性几何形状和不同材料特性来重建实验，以验证模拟和实验之间的一致性。
总体而言，对于大多数情况，MC 模拟的器官剂量值与测量值相符。X 射线源相对于模型的微小位移会导致器官剂量值偏差 6-135%，而皮肤剂量保持相对稳定。关于模型材料组成的影响，所有模拟模型中内部器官剂量值都低估了 12-20%。然而，皮肤剂量至少可以用两种材料以 1-8%的低偏差进行估计。
前瞻性参考剂量研究可能无法扩展到精确的患者特定剂量评估。因此，需要基于先进的患者建模和 MC 方法的在线器官剂量评估工具。
