Objective To compare and analyze the dose distribution of IMRT between fixed-gantry and unfixed-gantry dosimetric verification.

Methods Thirteen patients treated by IMRT were chosen randomly for this study.For each case, 2 different plans(fixed-gantry plan and unfixed-gantry plan)were worked out with Pinnacle 8.0 m planning system.The dose verification for each plan was carried out with Varian 23EX by using Detector729 with the octagonal phantom OCTAVIUS.The verification results of the dose distribution between the treatment planning system calculation and the measurement were done by the gamma analysis quantization with dose difference and distance to agreement of 3%(3 mm), 3%(4 mm) and 4%(4 mm) respectively, and the data were analyzed by Statistical Analysis System.

Results The repeatability of Detector729 was within 0.3%.According to the gamma analysis, the overall average passing rate of unfixed-gantry verification for the dosimetric deviation of 3%(3 mm), 3%(4 mm)and 4%(4 mm) were 91.2%, 92.4% and 95.6%, which were slightly lower compared with the passing rate of fixed-gantry verification of 2.2%(t=-2.04, P=0.053), 2.2%(t=-2.02, P=0.055) and 1.4%(t=-1.97, P=0.060) respectively, and the difference between the two verification methods was not statistically significant.

Conclusions The Detector729 is a reliable and accurate dosimeter.The two dosimetric verification methods of IMRT by using Detector729 are efficient and valuable.The radiotherapy department should select suitable and available dosimetric verification method for radiotherapy.