Impact of MLC error on dose distribution in SRS treatment of single-isocenter multiple brain metastases: comparison between DCAT and VMAT techniques

Background: Dynamic conformal arc therapy (DCAT) and volumetric modulated arc therapy (VMAT) can achieve near equal plan quality in single-isocenter multiple target stereotactic radiosurgery (SRS) for brain metastases. This study aimed to investigate the impact of multi-leaf collimator (MLC) errors during beam delivery on the dose distribution for each technique.

Materials and methods: A 10-mm diameter delineation of the three targets was employed on the computed tomography images of a head phantom, and the reference plans were created using the DCAT and VMAT. We simulated the systematic opened and closed MLC errors. 10 MLC error plans with different magnitudes of errors were created in each technique. We investigated the relationship between the magnitude of MLC errors and the change in dose-volume histogram parameters of the targets and normal brain tissue.

Results: The percentage change in the D_98% (Gy) and D_0.1% (Gy) of the target per millimeter of the MLC errors were 13.3% and 2.7% for the DCAT and 15.3% and 9.3% for the VMAT, respectively. The fluctuations of the maximum dose were very small for the DCAT compared to the VMAT. Changes in the V_12Gy (cc) of the normal brain tissue were 47.1%/mm and 53.2%/mm for the DCAT and VMAT, respectively, which are comparable changes for both techniques.

Conclusions: Although the impact of MLC errors on the target coverage and the normal brain tissue is comparable for both techniques, the internal dose of the targets generated by the DCAT technique is robust to the MLC errors.