Falco Maria Daniela, D'Andrea Marco, Strigari Lidia, D'Alessio Daniela, Quagliani Francesco, Santoni Riccardo, Bosco Alessia Lo
Department of Diagnostic Imaging, Tor Vergata University General Hospital, V.le Oxford 81, 00133 Rome, Italy.
Med Phys. 2012 Aug;39(8):4866-74. doi: 10.1118/1.4736806.
During radiological interventional procedures (RIP) the skin of a patient under examination may undergo a prolonged x-ray exposure, receiving a dose as high as 5 Gy in a single session. This paper describes the use of the OneDose(TM) cable-free system based on p-type MOSFET detectors to determine the entrance skin dose (ESD) at selected points during RIP.
At first, some dosimetric characteristics of the detector, such as reproducibility, linearity, and fading, have been investigated using a C-arc as a source of radiation. The reference setting (RS) was: 80 kV energy, 40 cm × 40 cm field of view (FOV), current-time product of 50 mAs and source to skin distance (SSD) of 50 cm. A calibrated PMX III solid state detector was used as the reference detector and Gafchromic(®) films have been used as an independent dosimetric system to test the entire procedure. A calibration factor for the RS and correction factors as functions of tube voltage and FOV size have been determined.
Reproducibility ranged from 4% at low doses (around 10 cGy as measured by the reference detector) to about 1% for high doses (around 2 Gy). The system response was found to be linear with respect to both dose measured with the PMX III and tube voltage. The fading test has shown that the maximum deviation from the optimal reading conditions (3 min after a single irradiation) was 9.1% corresponding to four irradiations in one hour read 3 min after the last exposure. The calibration factor in the RS has shown that the system response at the kV energy range is about four times larger than in the MV energy range. A fifth order and fourth order polynomial functions were found to provide correction factors for tube voltage and FOV size, respectively, in measurement settings different than the RS. ESDs measured with the system after applying the proper correction factors agreed within one standard deviation (SD) with the corresponding ESDs measured with the reference detector. The ESDs measured with Gafchromic(®) films were in agreement within one SD compared to the ESDs measured using the OneDose(TM) system, as well. The global uncertainty associated to the OneDose(TM) system established in our experiments, ranged from 7% to 10%, depending on the duration of the RIP due to fading. These values are much lower than the uncertainty commonly accepted for general diagnostic practices (20%) and of about the same size of the uncertainty recommended for practices with high risk of deterministic side effects (7%).
The OneDose(TM) system has shown a high sensitivity in the kV energy range and has been found capable of measuring the entrance skin dose in RIP.
在放射介入程序（RIP）中，接受检查的患者皮肤可能会经历长时间的X射线照射，单次照射剂量高达5 Gy。本文描述了基于p型MOSFET探测器的OneDose™无电缆系统在RIP期间选定部位确定皮肤入口剂量（ESD）的应用。
首先，使用C形臂作为辐射源研究了探测器的一些剂量学特性，如再现性、线性和衰退。参考设置（RS）为：80 kV能量、40 cm×40 cm视野（FOV）、50 mAs的电流-时间乘积以及50 cm的源皮距（SSD）。使用校准后的PMX III固态探测器作为参考探测器，并使用Gafchromic®胶片作为独立的剂量学系统来测试整个过程。确定了RS的校准因子以及作为管电压和FOV大小函数的校正因子。
再现性范围从低剂量时的4%（参考探测器测量约为10 cGy）到高剂量时的约1%（约2 Gy）。发现系统响应对于用PMX III测量的剂量和管电压均呈线性。衰退测试表明，与最佳读数条件（单次照射后3分钟）相比的最大偏差为9.1%，对应于一小时内四次照射，在最后一次照射后3分钟读取。RS中的校准因子表明，kV能量范围内的系统响应约为MV能量范围内的四倍。发现一个五次多项式函数和一个四次多项式函数分别为不同于RS的测量设置中的管电压和FOV大小提供校正因子。应用适当校正因子后，该系统测量的ESD与参考探测器测量的相应ESD在一个标准差（SD）内一致。与使用OneDose™系统测量的ESD相比，Gafchromic®胶片测量的ESD也在一个SD内一致。在我们的实验中确定的与OneDose™系统相关的总体不确定性范围为7%至10%，这取决于由于衰退导致的RIP持续时间。这些值远低于一般诊断实践中普遍接受的不确定性（20%），并且与确定性副作用高风险实践推荐的不确定性大小大致相同（7%）。
OneDose™系统在kV能量范围内显示出高灵敏度，并且已发现能够测量RIP中的皮肤入口剂量。
