Comparative Study Of Three Dosimetric Verification Tools For Intensity Modulated Radiotherapy

Intensity-Modulated Radiotherapy(IMRT) is becoming the standard radiation oncology treatment technique. Taking into consideration of the complexity of IMRT, more rigid and comprehensive quality assurance(QA) procedure is required to insure the treatment be delivered accurately. Pre-treatment patient plan dosimetry versification is necessary for the QA procedure. As one of most common IMRT dosimetric verification QA tools, Matri XX system is vastly used in clinical practice. Recently, some new QA tools are coming into clinical practice such as Portal Dosimetry(PD) based on Electronic Portal Imaging Device(EPID),and ADQ based on MLC log files. To test the reliability and consistency of these new tools comparing to Matri XX, we carried on this study.12 patients accepted Dynamic MLC(DMLC) IMRT were included in this study. Each field of the total 101 fields was verified separately using MatriXX, PD and ADQ. Total 101 DMLC IMRT fields QA dosimetric verification data. Gamma index analysis(3mm/3%, 10% low dose threshold) was carried out. Gamma pass rate, Maximum Gamma index and Average Gamma index were collected and compared, paired T-test and Spearman rank correlation coefficient analysis were performed in both group PD vs. MatriXX,and ADQ vs. MatriXX to determine the correlated factors of the QA tools. The Gamma pass rate, Average Gamma index and Maximum Gamma index of MatriXX were 98.67%±1.56%, 0.30±0.07, the Gamma passing rate, Average Gamma index and Maximum Gamma index for PD verification were 98.75%±1.11%、0.27±0.06 and 2.34±0.80,while that for ADQ were 99.82%±0.37%、0.05±0.03 和 0.82±0.49, separately. There was no significant difference in the Gamma pass rate between PD and MatriXX(p>0.05). Spearman rank correlation coefficient of PD and MatriXX QA verification Gamma passing rate was 0.5170, there was linear correlation between PD and MatriXX. Differently, there was significant difference in the Gamma pass rate between ADQ and MatriXX(p<0.05). Spearman rank correlation coefficient of ADQ and MatriXX QA verification Gamma pass rate was 0.1695, and there was no linear correlation between ADQ and MatriXX.In conclusion, there were high consistency and moderate correlation in the Gamma pass rates between the two QA tools PD and MatriXX. They could be considered to be equivalent. In addition, PD verification is more efficient. There were no consistency and correlation in the Gamma pass rates between the two QA tools ADQ and MatriXX. The difference was significant. But ADQ verification results indicated that MLC had better repeatability and stability among different treatment fractions. Further investigations are needed for ADQ’s application in clinical practice.