在有 MOSFET 的实现的高精力的光子放射疗法的外部剂量测量

• 作者: Dimitrios Kardamakis George Panayiotakis Georgia Malatara Harry Delis Kiki Theodorou Vassiliki Vlachopoulou
• 来源期刊: 世界放射学杂志：英文版（电子版）
• 学科: 医学
• 关键词: RADIOTHERAPY PERIPHERAL DOSE Metal oxide SEMICONDUCTOR field effect TRANSISTOR DOSIMETER
• 年，卷（期）: 2010,（11）
• 页码范围: 434-439
• 页数: 6页
• 分类号: R815

摘要

AIM:To study the peripheral dose(PD) from highenergy photon beams in radiotherapy using the metal oxide semiconductor field effect transistor(MOSFET) dose verification system.METHODS:The radiation dose absorbed by the MOSFET detector was calculated taking into account the manufacturer’s Correction Factor,the Calibration Factor and the threshold voltage shift.PD measurements were carried out for three different field sizes(5 cm×5 cm,10 cm×10 cm and 15 cm×15 cm) and for various depths with the source to surface distance set at 100 cm.Dose measurements were realized on the central axis and then at distances(1 to 18 cm) parallel to the edge of the field,and were expressed as the percentage PD(% PD) with respect to the maximum dose(dmax).The accuracy of the results was evaluated with respect to a calibrated 0.3 cm3 ionization chamber.The reproducibility was expressed in terms of standard deviation(s) and coefficient of variation.RESULTS:% PD is higher near the phantom surface and drops to a minimum at the depth of dmax,and then tends to become constant with depth.Internal scatter radiation is the predominant source of PD and the depth dependence is determined by the attenuation of the primary photons.Closer to the field edge,where internal scatter from the phantom dominates,the % PD increases with depth because the ratio of the scatter to primary increases with depth.A few centimeters away from the field,where collimator scatter and leakage dominate,the % PD decreases with depth,due to attenuation by the water.The % PD decreases almost exponentially with the increase of distance from the field edge.The decrease of the % PD is more than 60% and can reach up to 90% as the measurement point departs from the edge of the field.For a given distance,the % PD is significantly higher for larger field sizes,due to the increase of the scattering volume.Finally,the measured PD obtained with MOSFET is higher than that obtained with an ionization chamber with percentage differences being from 0.6% to 34.0%.However,when normal