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目的探索和评估自行开发研制的新型金属氧化物半导体场效应晶体管(MOSFET)探测器在体实时剂量测量中的应用特性。方法分别使用医科达加速器8、15MV光子线,以及6、8、12、18 MeV电子束刻度MOSFET探测器。根据探测器灵敏度随能量变化情况评估MOSFET探测器能量依赖性。使用8MV光子线在0～50 Gy范围内观察MOSFET探测器读数随累积剂量变化的线性情况,确定MOSFET探测器剂量测量的线性区间。将MOSFET探测器固定在圆柱形PMMA体模中央,顺时针每15°检测探测器信号响应,判断MOSFET探测器方向性。对1例乳腺癌放疗患者应用MOSFET探测器进行了全程剂量监测。在使用NE-2571指形电离室对该患者放疗计划剂量计算进行物理验证后,分别于首次治疗、每周1次治疗及最后1次治疗中应用MOSFET探测器测量患者体表吸收剂量,并将测量结果与该处计划剂量进行比较,确定乳腺癌三维放疗的总体剂量偏差。结果对8、15 MV光子线和6～18MeV电子束测量结果显示,MOSFET探测器灵敏度随能量变化的幅度＜2．5%。这表明MOSFET探测器对中高能射线具有较好的能量响应。在6 V门控电压状态下,MOSFET探测器在0～50 Gy的剂量范围内保持了较好的剂量线性,最大偏差＜3．0%。在每次测量前和测量后分别刻度MOSFET探测器并取其平均值可使其剂量线性误差控制在1%以内。该MOSFET探测器信号响应在270～90°之间呈现出各向同性,读数偏差＜1．5%。但在探测器背面(135～225°之间)的信号响应明显变小,背面与正面的读数偏差最大可达10．0%。应用于患者实时剂量监测的结果显示,实际测量剂量与计划剂量相比平均偏差2．8%,最大偏差＜5．0%,符合AAPM 13号报告对体外放疗剂量总不确定度的质量控制标准。结论该MOSFEYT探测器体积小,操作简单,对中高能辐射具有较好的能量响应和剂量线性,为治疗计划剂量验证和人体吸收剂量测量提供了一种较好的剂量工具。
Objective To explore and evaluate the application characteristics of a novel metal-oxide-semiconductor field-effect transistor (MOSFET) detector developed in-house in real-time dose measurement. Methods The Radosensitive 8,15 MV photon lines and the 6,8,12,18 MeV electron beam scaled MOSFET detectors were used respectively. MOSFET detector energy dependence is evaluated based on detector sensitivity as a function of energy. The 8 MV photon line was used to observe the linearity of the MOSFET detector readings as a function of cumulative dose over the 0-50 Gy range to determine the linear range of the MOSFET detector dose measurement. The MOSFET detector is fixed in the center of a cylindrical PMMA phantom, detecting the detector signal response every 15 ° clockwise to determine the direction of the MOSFET detector. One case of breast cancer radiotherapy patients with MOSFET detector for the entire dose monitoring. After NE-2571 finger ionization chamber was used to physically calculate the dose planning of radiotherapy in this patient, MOSFET detector was used to measure the body surface absorbed dose in the first treatment, once a week and the last one respectively. Measurement results and the Department of dose comparison to determine the overall dose of breast cancer three-dimensional radiation dose deviation. Results The measured results of 8,15 MV photons and 6 ~ 18 MeV electron beam show that the sensitivity of the MOSFET detector varies with energy by <2.5%. This indicates that the MOSFET detector has a good energy response to medium and high energy rays. At 6 V gate voltage, the MOSFET detector maintains a good dose linearity within the dose range of 0 to 50 Gy with a maximum deviation of <3.0%. Measure the MOSFET detector before and after each measurement and take the average value to control the dose linearity error within 1%. The MOSFET detector signal response is isotropic in the 270 ~ 90 °, reading deviation <1.5%. However, the signal response on the back of the detector (between 135 and 225 °) is significantly smaller and the deviation of the readings on the back and front is up to 10.0%. The results of real-time dose monitoring in patients showed that the actual measured dose was 2.8% less than the planned dose and the maximum deviation was less than 5.0%, which was consistent with the quality control standard of AAPM 13 on the total uncertainty of the dose of external radiotherapy . Conclusion The MOSFEYT detector has the advantages of small size, simple operation, good energy response and dose linearity to medium and high energy radiation, and provides a good dose tool for planning dose verification and body absorbed dose measurement.