A comparative analysis of Matrixx and EPID for dosimetric verification of intensity-modulated radiotherapy

Abstract

Objective To compare the dosimetric verification results of Varian Portal Dosimetry and Matrixx, and to assess the reliability of the clinical application of electronic portal imaging device (EPID) verification. Methods Varian TrueBeam linear accelerator, which was equipped with a 120-leaf multileaf collimator and an amorphous silicon EPID, as well as portal dose prediction software. IBA I′mRT Matrixx ion chamber array was used. EPID algorithm configuration, dose calibration, and testing before use were performed. The sliding-window protocol was used. There were 77 patients with tumors involving the head and neck (mainly nasopharyngeal carcinoma), mediastinum, abdomen, and pelvic cavity were selected. The verification plan of the portal dose was created with a source-detector distance of 100 cm, and the gantry angle was kept the same as the treatment plan. The verification plan was carried out in the TrueBeam machine, and the data were collected at the same time by EPID. Comparison between the measured and calculated dose images was performed, and the evaluation standard was gamma index (3%/3 mm). The paired t-test was used for difference analysis. Results For the 77 patients, the Gamma passing rates of both methods were above 97%. Except for head and neck carcinoma were a significant difference between the results of dosimetric results using EPID and Matrixx in intensity-modulated radiotherapy (P=0.018) other remaining all P> 0.05. Conclusions The dosimetric verification results of EPID are consistent with those of Matrixx. EPID can be used for dosimetric verification, and Matrixx ion chamber array can be used only in case of a low Gamma passing rate. Key words: Dosimetric verification; Portal dosimetry; Matrixx