Kinhikar Rajesh A, Pai Rajeshree, Master Zubin, Deshpande Deepak D
Department of Medical Physics, Tata Memorial Centre, Parel, Mumbai, India.
J Cancer Res Ther. 2009 Oct-Dec;5(4):284-9. doi: 10.4103/0973-1482.59911.
To characterize metal oxide semiconductor field-effect transistors (MOSFETs) for a 6-MV photon beam with a first helical tomotherapy Hi-Art II unit in India.
Standard sensitivity MOSFETs were first calibrated and then characterized for reproducibility, field size dependence, angular dependence, fade effects, and temperature dependence. The detector sensitivity was estimated for static as well as rotational modes for three jaw settings (1.0 cm x 40 cm, 2.5 cm x 40 cm, and 5 cm x 40 cm) at 1.5-cm depth with a source-to-axis distance (SAD) of 85 cm in virtual water slabs. The A1SL ion chamber and thermoluminescence dosimeters (TLDs) were used to compare the results.
No significant difference was found in the detector sensitivity for static and rotational procedures. The average detector sensitivity for static procedures was 1.10 mV/cGy (SD 0.02) while it was 1.12 mV/cGy (SD 0.02) for rotational procedures. The average detector sensitivity found was the same within the experimental uncertainty for static and rotational dose deliveries. The MOSFET reading was consistent and its reproducibility was excellent (+0.5%) while there was no significant dependence of field size. The angular dependence of less than 1.0% was observed. There was negligible fading effect of the MOSFET. The MOSFET response was found independent of temperature in the range 18 degrees-30 degrees. The ion chamber readings were assumed to be a reference for the estimation of the MOSFET calibration factor. The ion chamber and the TLD were in good agreement (+2%) with each other.
This study deals only with the measurements and calibration performed on the surface of the phantom. MOSFET was calibrated and validated for phantom surface measurements for a 6-MV photon beam generated by a tomotherapy machine. The sensitivity of the detector was the same for both modes of treatment delivery with tomotherapy. The performance of the MOSFET was validated for and satisfactory for the helical tomotherapy Hi-Art II unit. However, MOSFET may be used for in vivo surface dosimetry only after it is calibrated under the conditions replicating as much as possible the manner in which the dosimeter will be used clinically.
使用印度的首台螺旋断层放射治疗Hi-Art II设备对6兆伏光子束的金属氧化物半导体场效应晶体管（MOSFET）进行特性描述。
首先对标准灵敏度的MOSFET进行校准，然后对其可重复性、射野大小依赖性、角度依赖性、衰退效应和温度依赖性进行特性描述。在虚拟水模体中，源轴距（SAD）为85厘米、深度为1.5厘米处，针对三种射野设置（1.0厘米×40厘米、2.5厘米×40厘米和5厘米×40厘米），估计静态和旋转模式下探测器的灵敏度。使用A1SL电离室和热释光剂量计（TLD）比较结果。
在静态和旋转程序中，探测器灵敏度未发现显著差异。静态程序的平均探测器灵敏度为1.10毫伏/厘戈瑞（标准差0.02），而旋转程序为1.12毫伏/厘戈瑞（标准差0.02）。在静态和旋转剂量输送的实验不确定度范围内，所发现的平均探测器灵敏度相同。MOSFET读数一致，其可重复性极佳（±0.5%），而射野大小无显著依赖性。观察到角度依赖性小于1.0%。MOSFET的衰退效应可忽略不计。在18摄氏度至30摄氏度范围内，发现MOSFET响应与温度无关。假定电离室读数为估计MOSFET校准因子的参考。电离室和TLD相互之间一致性良好（±2%）。
本研究仅涉及在模体表面进行的测量和校准。对MOSFET进行了校准并验证其可用于断层放射治疗机产生的6兆伏光子束的模体表面测量。对于断层放射治疗的两种治疗模式，探测器的灵敏度相同。MOSFET的性能经过验证，对于螺旋断层放射治疗Hi-Art II设备而言令人满意。然而，只有在尽可能模拟剂量计临床使用方式的条件下进行校准后，MOSFET才可用于体内表面剂量测定。
Zotero 插件