Application of semiconductor matrix in synchronization test in helical tomotherapy / 中华放射肿瘤学杂志

ABSTRACT

Objective To investigate how to use the ArcCHECK to complete synchronization test in helical tomotherapy(HT). Methods According to the synchronization test suggested by AAPM TG148, three aspects should be tested.(1)Gantry angle consistencyArcCHECK device in the long axis was perpendicular to the rotation plane using virtual isocenter positioning. A delivery sequence was defined with a slice width of 2.5 cm,a pitch of 0.1,and a minimum of 40 rotations. The control sinogram was set to open the middle two leaves(No. 32 and 33)at projections centered at 0°, 120°, and 240°.(2)Couch speed uniformityThe ArcCHECK was fixed on the treatment couch by positioning the long axis in the movement direction of couch. An irradiation was done with a static gantry in the 0° position, the collimation set to 1 cm,and all MLC leaves open. A couch travel distance of 20 cm was programmed using a clinically common couch speed(0.3-0.5 mm/s for 2.5 cm treatment slice width)in the course of irradiation.(3) Synchronization of couch translation and gantry rotationIn this test,a rotational irradiation was used with the nominal 1.0 cm beam and a pitch of 1 for 13 rotations. The control sonogram was set to open all the leaves for a half rotation on the second,seventh,and twelfth rotations. The initial collected data were used as the baseline data of parameters. The subsequent measurements were compared with the baseline data using the point to point absolute dose pass rates of DD(dose difference,1%). Results The gantry angle consistency could check the correct initial angles at the beginning of the treatment and the ability to reproduce the projection every rotation.There were six parallel and straight high-dose regions in ArcCHECK software.In the couch speed uniformity test,the relative dose in the long axis in the high-dose regions was changed less than 2%. In the synchronization test of couch translation and gantry rotation,three parallel high-dose regions with the same separation spacing were present in the ArcCHECK software. The synchronization tests were done twenty-eight times in the second,seventh, and twelfth irradiation rotations and the average pass rates were 93.2%±1.5%,93.7%±1.1%,and 93.5%±1.3%,respectively. Conclusions The ArcCHECK device is a suitable alternative method for performing the synchronization test in HT due to its lower workload and costs compared with the film.