A clinical test and application research of IMRT dose verification system based on patient' s anatomical structure and on-line dosimetry

Objective To test a three-dimensional dose verification system,which reconstructing dose to anatomy based on modeling and online measurements ( RDBMOM ),and to evaluate the accuracy and feasibility of its application in clinical intensity-modulated radiotherapy (IMRT) quality assurance.Methods Phantom plans of regular and irregular fields were selected for the testing.All test plans were implemented and the dose distributions were measured using the thimble ion-chamber and two-dimensional ion-chamber array,the accuracy of RDBMOM were then evaluated by comparing the corresponding results.Two practical treated nasopharyngeal carcinoma IMRT plans were verified with RDBMOM and the clinic significancy were valued.Results Compared with measurements of the thimble ion-chamber,deviations of RDBMOM were within 1％ in all tested cases except small field of 3 cm ×3 cm.The largest deviation of reconstructed dose in IMRT cases was 2.12％.The dose profile reconstructed by RDBMOM coincided with the measurement using two-dimensional ion-chamber array.The γ rates (3％/3 mm) were 94.56％ - 100％.The RDBMOM verification of IMRT cases shown that the γ rate ＞ 99％ in total and ＞ 98％ in planning target volume,deviation in D95 ＜0.4％,but the largest deviations in mean dose of the parotids and lens were 2.97％ and 59.58％ respectively.Conclusions Accuracy of the tested system satisfies the demand of IMRT dose verification.RDBMOM is able to provide information of volumetric dosimctry and anatomical location of dose error,which is benefit for evaluating the clinical value of verification results. Key words: Intensity-modulated radiotherapy; Quality assurance; Three-dimensional dose verification; Dosimetry,on-line