Butson M J, Rozenfeld A, Mathur J N, Carolan M, Wong T P, Metcalfe P E
Illawarra Cancer Care Centre, Department of Radiotherapy, Wollongong, New South Wales, Australia.
Med Phys. 1996 May;23(5):655-8. doi: 10.1118/1.597702.
Radiotherapy x-ray and electron beam surface doses are accurately measurable by use of a MOS-FET detector system. The MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is approximately 200-microns in diameter and consists of a 0.5-microns Al electrode on top of a 1-microns SiO2 and 300-microns Si substrate. Results for % surface dose were within +/- 2% compared to the Attix chamber and within +/- 3% of TLD extrapolation results for normally incident beams. Detectors were compared using different energies, field size, and beam modifying devices such as block trays and wedges. Percentage surface dose for 10 x 10-cm and 40 x 40-cm field size for 6-MV x rays at 100-cm SSD using the MOSFET were 16% and 42% of maximum, respectively. Factors such as its small size, immediate retrieval of results, high accuracy attainable from low applied doses, and as the MOSFET records its dose history make it a suitable in vivo dosimeter where surface and skin doses need to be determined. This can be achieved within part of the first fraction of dose (i.e., only 10 cGy is required.)
使用MOS-FET探测器系统可精确测量放射治疗的X射线和电子束表面剂量。MOSFET（金属氧化物半导体场效应晶体管）直径约为200微米，由位于1微米SiO2和300微米Si衬底之上的0.5微米铝电极组成。对于垂直入射束，与Attix电离室相比，表面剂量百分比结果在±2%以内，与热释光剂量计外推结果相比在±3%以内。使用不同能量、射野大小以及诸如挡块托盘和楔形板等射束修正装置对探测器进行了比较。在100厘米源皮距下，使用MOSFET测量6兆伏X射线10×10厘米和40×40厘米射野大小的表面剂量百分比分别为最大值的16%和42%。其尺寸小、结果可即时获取、低剂量应用时可达到高精度以及MOSFET能记录其剂量历史等因素，使其成为测定表面和皮肤剂量时合适的体内剂量计。这可在剂量的第一部分内实现（即仅需10厘戈瑞）。
