TomoDose半导体探测器特性分析及其在Tomotherapy质控中的应用研究

目的 评估TomoDose半导体探头特性及其在检测Tomotherapy床速和Profile稳定性方面的应用,以期用其便捷、高效地对Tomotherapy进行质控。方法 结合等效水模体对TomoDose探头的剂量线性响应、每脉冲剂量响应、角度依赖性和射野大小依赖性进行测量,并与0.057 cm³A1SL指型电离室进行比较分析。以0.000 5 s为间隔预设5个组床速来检测TomoDose对床速检测的灵敏度,选取7例不同床速的临床计划数据对其进行检验。用TomoDose和等效水模体采集Tomotherapy年检中的Profile数据(测量条件和采用水箱时一致),分别在Jaw为1.0、2.5、5.0 cm状态下,在水下深度为15、50、100、150、200 mm处测量x轴向和y轴向的射线束Profile,并采用Gamma分析(2%/1 mm)方法评估TomoDose和水箱所测得的Profile数据。结果 TomoDose半导体探头和电离室在出束时间≤30 s范围内对剂量的响应呈线性;每脉冲剂量响应与电离室的差异<2%,两者响应趋势一致;其存在角度响应,在±60°范围内角度响应最大相差2.53%;Jaw=5.0 cm时不同射野大小下两者响应差异随着射野减小而增大,5.0 cm×2.5 cm时最大为0.78%。TomoDose可识别0.5 mm进床距离误差,床速检测偏差值<0.6%。对于Profile稳定性检测:在x轴向上,水下深度为15 mm时Jaw取任何值,均有γ<1;取其他值时主射野区(离轴距<200 mm的区域)内均有γ<1,射野边缘半影区(离轴距>200 mm的区域)γ较大,出现γ>1的情况。在y轴向上,3个射野宽度下所有的Profile对比结果均显示γ值在射野边缘较大,但所有情况下均有γ<1。结论 TomoDose适合对Tomotherapy进行相关质控,能够精确测量Tomotherapy的床速,能够准确监测Tomotherapy射束Profile的稳定性,并且质控过程便捷而高效。

Characteristics and clinical application of the TomoDose diode array for quality control of Tomotherapy

Objective To evaluate the dosimetric characteristics of the TomoDose diode and its application in detecting the couch velocity and assessing the beam Profile stability for convenient and efficient quality control of Tomotherapy. Methods Fundamental properties of the TomoDose detector,such as dose linearity,dose per pulse dependence,directional dependence and field size dependence were tested by the water-equivalent phantom and the results were statistically compared with those measured by the ion-chamber (0.057 cm³,A1SL).Five different couch velocities with a time interval of 0.0005 s were designed to test the sensitivity of TomoDose for detecting the couch velocity,and then the clinical data of 7 patients with different couch velocities were selected to verify the test accuracy. The beam profile of three different jaws of 1.0,2.5 and 5.0 cm were measured using TomoDose with water-equivalent phantom in the x and y directions under the same conditions as water tank with an underwater depth of 15,50,100,150 and 200 mm,respectively. The Profile data obtained by water tank and TomoDose were evaluated using the Gamma (γ) evaluation method with the 2%/1 mm criterion. Results The dose linearity of the TomoDose and ion chamber was in a linear pattern within the beam-on-time≤30 s. The difference between the TomoDose and ion chamber was less than 2% for the dose per pulse dependence,and the response trends of them were consistent. TomoDose showed angular response dependence with a maximum difference of 2.53% for the gantry angle of ±60°.For the field size dependence,the response difference between the TomoDose and ion chamber was increased with the decreasing field size when the Jaw was 5.0 cm,and the maximum deviation was 0.78% when the field size was 5.0 cm×2.5 cm. TomoDose could detect the couch distance error of 0.5 mm,and determine the couch velocity deviation of< 0.6%.For the Profile stability testing:In the x direction,there was always γ<1 at the underwater depth of 15 mm for all values of Jaw;when the underwater depth was not 15 mm,there was always γ<1 in the main beam region (off-axis distance< 200 mm),whereas in the penumbra region (off-axis distance> 200 mm),the value of γ was larger and even with γ>1.In the y direction,all comparison results of Profile under three field width demonstrated that γ index was larger on the edge of beam,whereas γ<1 was found in all cases. Conclusions TomoDose is suitable f or the quality control of Tomotherapy,which can accurately measure the couch velocity,precisely monitor the stability of beam Profile of Tomotherapy and complete the quality control process in a convenient and efficient manner.