Skin dose measurements using MOSFET and TLD for head and neck patients treated with tomotherapy

The purpose of this work was to estimate skin dose for the patients treated with tomotherapy using metal oxide semiconductor field-effect transistors (MOSFETs) and thermoluminescent dosimeters (TLDs). In vivo measurements were performed for two head and neck patients treated with tomotherapy and compared to TLD measurements. The measurements were subsequently carried out for five days to estimate the inter-fraction deviations in MOSFET measurements. The variation between skin dose measured with MOSFET and TLD for first patient was 2.2%. Similarly, the variation of 2.3% was observed between skin dose measured with MOSFET and TLD for second patient. The tomotherapy treatment planning system overestimated the skin dose as much as by 10–12% when compared to both MOSFET and TLD. However, the MOSFET measured patient skin doses also had good reproducibility, with inter-fraction deviations ranging from 1% to 1.4%. MOSFETs may be used as a viable dosimeter for measuring skin dose in areas where the treatment planning system may not be accurate.     

Feasibility study of using MOSFET detectors for in vivo dosimetry during permanent low-dose-rate prostate implants

PURPOSE: To investigate the feasibility of using new micro-MOSFET detectors for QA and in vivo dosimetry of the urethra during transperineal interstitial permanent prostate implants (TIPPB). METHODS AND MATERIALS: This study involves measurements for several patients who have undergone the implant procedure with iodine-125 seeds. A new micro-MOSFET detector is used as a tool for in vivo measurement of the initial dose rate within the urethra. MOSFETs are calibrated using a single special order calibration seed. The angular response is investigated in a 100 kVp X-ray beam. RESULTS: micro-MOSFETs are found to have a calibration factor of 0.03 cGy/mV for low energy X-rays and a high isotropic response (within 2.5%). Prostate volume and shape changes during TIPPB due to edema caused by the trauma of needle insertion, making it difficult to achieve the planned implant geometry and hence the desired dose distribution. MOSFET measurements help us to evaluate the overall quality of the implant, by analyzing the maximum dose received by urethra, the prostate base coverage, the length of the prostatic urethra that is irradiated, and the apex coverage. CONCLUSIONS: We demonstrate that ease of use, quick calibration and the instantaneous reading of accumulated dose make micro-MOSFETs feasible for in vivo dosimetry during TIPPB.     

Effects of JFET Region Design and Gate Oxide Thickness on the Static and Dynamic Performance of 650 V SiC Planar Power MOSFETs

650 V SiC planar MOSFETs with various JFET widths, JFET doping concentrations, and gate oxide thicknesses were fabricated by a commercial SiC foundry on two six-inch SiC epitaxial wafers. An orthogonal P+ layout was used for the 650 V SiC MOSFETs to reduce the ON-resistance. The devices were packaged into open-cavity TO-247 packages for evaluation. Trade-off analysis of the static and dynamic performance of the 650 V SiC power MOSFETs was conducted. The measurement results show that a short JFET region with an enhanced JFET doping concentration reduces specific ON-resistance (Ron,sp) and lowers the gate-drain capacitance (Cgd). It was experimentally shown that a thinner gate oxide further reduces Ron,sp, although with a penalty in terms of increased Cgd. A design with 0.5 μm half JFET width, enhanced JFET doping concentration of 5.5×1016 cm⁻³, and thin gate oxide produces an excellent high-frequency figure of merit (HF-FOM) among recently published studies on 650 V SiC devices.     

Characterization of responses and comparison of calibration factor for commercial MOSFET detectors

A commercial metal oxide silicon field effect transistor (MOSFET) dosimeter of model TN502-RD has been characterized for its linearity, reproducibility, field size dependency, dose rate dependency, and angular dependency for Cobalt-60 (⁶⁰Co), 6-MV, and 15-MV beam energies. The performance of the MOSFET clearly shows that it is highly reproducible, independent of field size and dose rate. Furthermore, MOSFET has a very high degree of linearity, with r-value > 0.9 for all 3 energies. The calibration factor for 2 similar MOSFET detectors of model TN502-RD were also estimated and compared for all 3 energies. The calibration factor between the 2 similar MOSFET detectors shows a variation of about 1.8% for ⁶⁰Co and 15 MV, and for 6 MV it shows variation of about 2.5%, indicating that calibration should be done whenever a new MOSFET is used. However, the detector shows considerable angular dependency of about 8.8% variation. This may be due to the variation in radiation sensitivity between flat and bubble sides of the MOSFET, and indicates that positional care must be taken while using MOSFET for stereotactic radiosurgery and stereotactic radiotherapy dosimetric applications.     

金属氧化物半导体场效应晶体管测量面罩对表面剂量的影响

目的 使用金属氧化物半导体场效应晶体管(metal oxide semiconductor field effect transistor,MOSFET)探测器测量面罩对表面剂量的影响。方法 选用6MV和15MV X射线进行照射,分为有面罩组和无面罩组,用MOSFET分别测量,每组测5次,共测量5种不同密度的面罩。结果 使用面罩后表面剂量明显增加;不同面罩对表面剂量的影响程度不同。结论 使用面罩后射线的剂量建成区出现变化,表面剂量明显提高。临床治疗中需要适当关注皮肤表面的放射反应。     

Three-micrometer-diameter needle electrode with an amplifier for extracellular in vivo recordings

Microscale needle-electrode devices offer neuronal signal recording capability in brain tissue; however, using needles of smaller geometry to minimize tissue damage causes degradation of electrical properties, including high electrical impedance and low signal-to-noise ratio (SNR) recording. We overcome these limitations using a device assembly technique that uses a single needle-topped amplifier package, called STACK, within a device of ∼1 × 1 mm². Based on silicon (Si) growth technology, a <3-µm-tip-diameter, 400-µm-length needle electrode was fabricated on a Si block as the module. The high electrical impedance characteristics of the needle electrode were improved by stacking it on the other module of the amplifier. The STACK device exhibited a voltage gain of >0.98 (−0.175 dB), enabling recording of the local field potential and action potentials from the mouse brain in vivo with an improved SNR of 6.2. Additionally, the device allowed us to use a Bluetooth module to demonstrate wireless recording of these neuronal signals; the chronic experiment was also conducted using STACK-implanted mice.

Microscale needle-electrode devices, which allow brain tissue to be penetrated and electrical signals of neurons and cells to be recorded, have been a powerful means of understanding how the brain forms complete circuits, making significant contributions to neuroscience. Micro- and nanoscale fabrication technologies offer miniaturization of the needle-electrode geometry. The two-dimensional fabrication process produces a shank type of ∼40-µm-width needle electrode, called a “Michigan probe” (1, 2). This type of electrode is followed by a complementary metal–oxide–semiconductor (CMOS) amplifier array on each shank (3, 4). A wafer-dicing–based fabrication process produces the other type, a three-dimensional ∼80-µm-diameter needle array, called the “Utah array” (5, 6), which demonstrates the brain–machine interface (7, 8). However, these fabrication technologies face the issue of further miniaturization of the needle geometry, which is an important property of the electrode in terms of biocompatibility and application to chronic device implantation (9).Saxena et al. reported that a 50-μm-thick Michigan probe enhanced the blood–brain barrier breach in electrode-implanted rats (10). Although the size of the needle is < 50 µm, an object with a dimension >20 µm is still subject to disruption of the local communication between glia, releasing proinflammatory cytokines and recruiting additional activated microglia and reactivated astrocytes (11–13). However, further needle geometry reduction to <10 µm leads to no major traumatic injury in the tissue (14).On the basis of these findings, an “ultrasmall” needle electrode with a <10-µm diameter is necessary as the next step toward minimally invasive neuronal recording of the brain. A needle electrode with a diameter of ∼8.6 µm was fabricated using 7-µm-diameter carbon fibers and additional coating processes, demonstrating reduced chronic reactive tissue responses while a single neuron is recorded (15). A further small-needle electrode was produced by a silicon (Si) growth technology (gold-catalyzed vapor–liquid–solid [VLS] growth), resulting in needle-electrode diameters of ∼7 µm (16, 17) and ∼5 µm (18).Needle-electrode miniaturization degrades the electrical property of signal-to-noise ratio (SNR) in the neuronal recording. Fig. 1A shows the fabrication process of the <10-µm-diameter needle electrode using an ∼1-µm-diameter Si needle and subsequent coatings of metal and insulating layers (e.g., platinum [Pt] and parylene). This electrode technology allows the needle to be reduced to <3 µm in diameter (18, 19). However, the electrolyte/metal interfacial electrical impedance of the electrode increased with a decrease in the area of the recording site of the metal, attenuating the amplitude of neuronal signals (17, 20) and degrading the SNR of the recording (Fig. 1 B, 1). Although the electrode’s impedance can be reduced using a low-impedance material [e.g., platinum black (Pt black) (21), iridium oxide, and poly(3,4-ethylenedioxythiophene) (PEDOT) (22)], this low-impedance material must be deposited on the needle, increasing the size (diameter) of the needle itself and limiting the needle miniaturization. Further, the reduction of the electrode’s impedance is limited by both the area of the needle tip and the impedance of the deposited material.Open in a separate windowFig. 1.A 3-µm-diameter needle electrode with an amplifier for extracellular recordings. (A) SEM images of an ∼1-µm-diameter Si needle by Si growth technology (A, 1) and schematics of electrode fabrication (A, 2). (B, 1) Equivalent circuit model of the needle electrode in the neuronal recording. The recording system between the electrode and the recording amplifier consists of the needle’s electrolyte/metal interfacial electrical impedance, Z_e, and parasitic impedances of device interconnection, Z_l, cable capacitance, Z_Ca and input impedance of the amplifier, Z_in. (B, 2) Equivalent circuit model of the needle electrode with a head-stage AMP to improve electrical properties in the neuronal recording. (C) Schematics of the assembly technique of the STACK device, in which a module of the microneedle electrode is stacked on the other AMP module with a flexible interposer between them.Another method of improving the electrical properties of such an ultrasmall-needle electrode is to design a signal-buffering amplifier at the head stage of the electrode device (Fig. 1 B, 2 and SI Appendix, Text ST1 and Fig. S1). We demonstrated the on-chip integration of a metal–oxide–semiconductor field-effect transistor (MOSFET) amplifier with these needle electrodes, assembled by the post-MOSFET process of the VLS growth of the Si microneedle, using either the (111)-Si substrate (23, 24) or a hybrid substrate of (100)-top-Si/buried oxide/(111)-handle-Si (25, 26). However, both the needle and the amplifier were designed to be on the same surface side of the chip. Hence, the device had a relatively large area [e.g., 8 × 3 mm² for the surface-sided device interconnections (17, 18)], which had to be miniaturized to reduce the removal area of the cranium, particularly for a small brain (such as that of mice).We propose an assembly technique in which a module of a <3-µm-tip-diameter microneedle electrode is stacked on another amplifier module, called the single needle-topped amplifier package (STACK) device, to overcome issues related to the electrical properties of an ultrasmall needle electrode of less than 10 µm in diameter and the device area (Fig. 1C). We designed the device to be within ∼1 × 1 mm² for in vivo recording of neuronal activities in the mouse brain.     

基于MOSFET电路的非视觉感光系统建模及其照明应用

目的为合理解释非视觉感光系统响应量与光照之间的关系,探讨LED照度光环境对学习者学习效率及疲劳度的影响。方法首先利用等效类比的方法建立了基于MOSFET电路的非视觉感光系统模型,然后利用Multisim 12.0软件进行了MOSFET电路仿真,并验证了非视觉感光系统与MOSFET电路模型一致性。最后结合新型学习工具——平板显示器,通过改变光环境照度,采用安菲莫夫字母表测试了6名学习者的学习效率与疲劳度。结果结果显示,学习效率随着照度增加而增加,照度在700 lx附近达到最大,视疲劳与脑疲劳较小。结论利用本文所建立的基于MOSFET电路的非视觉感光系统模型,较好地解释了光感受系统作用机制,并综合考虑学习效率、视疲劳和脑疲劳三方面因素,提出合理照明建议:在多数学习任务情境下,应尽可能选择700 lx附近LED光源作为光环境照度。