UZ Brussel, Oncologisch Centrum, Radiotherapie, Brussels, Belgium.
Phys Med Biol. 2010 Feb 21;55(4):N97-109. doi: 10.1088/0031-9155/55/4/N01. Epub 2010 Jan 20.
The purpose of this note is to report the feasibility and clinical validation of an in-house developed MOSFET dosimetry system and describe an integrated non-destructive reset procedure. Off-the-shelf MOSFETs are connected to a common PC using an 18 bit/analogue-input and 16 bit/output data acquisition card. A reading algorithm was developed defining the zero-temperature-coefficient point (ZTC) to determine the threshold voltage. A wireless interface was established for ease of use. The reset procedure consists of an internal circuit generating a local heating induced by an electrical current. Sensitivity has been investigated as a function of bias voltage (0-9 V) to the gate. Dosimetric properties have been evaluated for 6 MV and 15 MV clinical photon beams and in vivo benchmarking was performed against thermoluminescence dosimeters (TLD) for conventional treatments (two groups of ten patients for each energy) and total body irradiation (TBI). MOSFETS were pre-irradiated with 20 Gy. Sensitivity of 0.08 mV cGy(-1) can be obtained for 200 cGy irradiations at 5 V bias voltage. Ten consecutive measurements at 200 cGy yield a SD of 2.08 cGy (1.05%). Increasing the dose in steps from 5 cGy to 1000 cGy yields a 1.00 Pearson correlation coefficient and agreement within 2.0%. Dose rate dependence (160-800 cGy min(-1)) was within 2.5%, temperature dependence within 2.0% (25-37 degrees C). A strong angular dependence has been observed for gantry incidences exceeding +/-30 degrees C. Dose response is stable up to 50 Gy (saturation occurs at approximately 90 Gy), which is used as threshold dose before resetting the MOSFET. An average measured-over-calculated dose ratio within 1.05 (SD: 0.04) has been obtained in vivo. TBI midplane-dose assessed by entrance and exit dose measurements agreed within 1.9% with ionization chamber in phantom, and within 1.0% with TLD in vivo. An in-house developed resettable MOSFET-based dosimetry system is proposed. The system has been validated and is currently used for in vivo entrance dose measurement in clinical routine for simple (open field) treatment configurations.
本注释旨在报告内部开发的 MOSFET 剂量测定系统的可行性和临床验证，并描述一种集成的无损重置程序。市售的 MOSFET 使用 18 位/模拟输入和 16 位/输出数据采集卡连接到通用 PC。开发了一种读取算法，定义了零温度系数点 (ZTC) 以确定阈值电压。建立了无线接口以方便使用。重置程序包括由电流产生的内部电路引起的局部加热。已经研究了作为偏置电压（0-9V）函数的灵敏度。已经针对 6MV 和 15MV 临床光子束评估了剂量学特性，并针对常规治疗（每组十个患者，每个能量）和全身照射（TBI）对热释光剂量计（TLD）进行了体内基准测试。MOSFET 用 20Gy 预先照射。在 5V 偏置电压下，可获得 200cGy 辐照时 0.08mV cGy(-1)的灵敏度。在 200cGy 下进行十个连续测量，得出 SD 为 2.08cGy（1.05%）。从 5cGy 到 1000cGy 逐步增加剂量，得出 1.00 Pearson 相关系数，并且在 2.0%以内一致。剂量率依赖性（160-800cGy min(-1))在 2.5%以内，温度依赖性在 2.0%以内（25-37°C)。对于超过 +/-30°C 的机架入射角，观察到强烈的角度依赖性。在 50Gy 之前，剂量响应是稳定的（饱和发生在大约 90Gy 处），这用作重置 MOSFET 之前的阈值剂量。在体内获得了平均测量-计算剂量比在 1.05（SD：0.04）以内。在体模中，通过入口和出口剂量测量评估的 TBI 中平面剂量与电离室一致，在体内与 TLD 一致，相差 1.0%以内。提出了一种内部开发的可重置 MOSFET 基剂量测定系统。该系统已经过验证，目前用于临床常规的简单（开放场）治疗配置的体内入口剂量测量。
