The impact of plan complexity on dose delivery deviations resulting from multileaf collimator positioning errors in...

This study aimed to assess the effect of plan complexity on dosimetric alterations induced by multileaf collimator (MLC) misplacements in volumetric modulated arc therapy (VMAT).

Volumetric modulated arc therapy plans for 14 cervical and 10 lung cancer cases were reoptimized utilizing 3 distinct aperture shape controller (ASC) settings (none, very high, and very low), resulting in 3 plan groups: ASC-none, ASC-vh, and ASC-vl. Four types of MLC position errors were simulated: total shifts (Type 1), open/closed (Type 2), right-side shifts (Type 3), and left-side shifts (Type 4). Plan complexity was assessed using the small aperture score (SAS). Dose deviations resulting from various MLC positioning errors and SAS values were calculated and compared among the 3 ASC groups.

The variations in planning target volume (PTV) D95% for cervical cancer were approximately 0.6%, 3.7%, 1.9%, and 1.8% per millimetre for Types 1-4 errors, respectively. In the case of lung cancer, the changes were 2.3%, 9.3%, 5.3%, and 4.6% per millimetre. The ASC-vh and ASC-vl groups exhibited significantly reduced dose changes and SAS values in response to MLC errors, as compared to the ASC-none group (P < .05).

Highly complex plans exhibit greater dose sensitivity to MLC positional errors. The application of ASC proves effective in reducing plan complexity and mitigating the influence of MLC errors on dose deviation.

By elucidating the relationship between dosimetric impacts from MLC errors and plan complexity, this study offers valuable guidance for the design of radiotherapy plans, helping to enhance the accuracy and effectiveness of VMAT treatments.