Characteristics and clinical application of the TomoDose diode array for quality control of Tomotherapy / 中华放射肿瘤学杂志

ABSTRACT

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,A 1SL).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 testingIn 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＞ l.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.