Abstract
Objective To investigate the dosimetric effect of accelerator gantry rotation angle errors, collimator and multileaf collimator (MLC) leaf position errors on volumetric-modulated arc therapy (VMAT) for cervical cancer. Methods A total of 10 patients with cervical cancer were selected. The plan.Trail file of each clinical plan was extracted from the Pinnacle3 V9.2 planning system of USA Philips, then the operating parameters of tach control point were read and modified by Matlab programs, and thus the operating error of the accelerator was simulated. Results In this paper, it was discovered that systematic accelerator gantry rotation angle errors, systematic collimator position errors and systematic MLC shift errors which led to the maximum changes of the PTV dose limit were 0.16%, 0.46% and 0.57%, respectively, and the maximum changes of the dose limit of organs at risk (OAR) were 0.38%, -1.32% and -0.44%, respectively. When the systematic MLC gap width errors were±0.5, ±1 and±2 mm, respectively, the maximum changes of PTV dose were 2.11%, 3.04% and 6.03%, respectively, while the maximum changes of the OAR average dose were 2.17%, 3.92% and 7.97%, respectively. Furthermore, the dose limits of PTV and OAR showed a strong linear correlation with MLC open or close errors(t=21.201~90.562, P<0.05). If actual errors of each parameter of accelerator were introduced, the maximum changes of PTV and OAR dose limits were 0.16% and 1.30%, respectively, and conformity index (CI) and homogeneity index (HI) were barely changed. Conclusions No significant effect was found for systematic accelerator gantry rotation angle errors, systematic collimator position errors and systematic MLC shift errors for cervical cancer VMAT patients. However, there is a high sensitivity to dose distribution for MLC open or close errors. Therefore, it is necessary to pay more attention on the quality control of the accelerator running in particular MLC position errors to ensure the therapeutic accuracy. Key words: Dosimetry; Volumetric modulated arc therapy; Linear accelerator; Position accuracy
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