Abstract

AimThe correlation between the MLC QA (IBA Dosimetry, Germany) results of the picket fence test created with intentional errors and the patient's quality assurance (QA) evaluation was investigated to assess the impact of multileaf collimator (MLC) positioning error on patient QA.Materials and methodsThe picket fence, including error-free and intentional MLC errors, defined in Bank In, Bank Out, and Bank Both were analyzed using MLC QA. The QA of 15 plans consisting of stereotactic radiosurgery (SRS), stereotactic body radiotherapy (SBRT), and conventionally fractionated volumetric-modulated arc therapy (VMAT) acquired with electronic portal imaging devices (EPID) was evaluated in the presence of error-free and MLC errors. The QA of plans were analyzed with 2%/2 mm and 3%/3 mm criteria.ResultsThe passing rates of the picket fence test were 97%, 92%, 91%, and 87% for error-free and intentional errors. The criterion of 3%/3 mm wasn’t able to detect an MLC error for either SRS/SBRT or conventionally fractionated VMAT. The criterion of 2%/2mm was more sensitive to detect MLC error for the conventionally fractionated VMAT than SRS/SBRT. While only two of SBRT plans had <90%, four of conventionally fractionated VMAT plans had a <90% passing rate.ConclusionWe found that the systematic MLC positioning errors defined with picket fence have a smaller but measurable impact on SRS/SBRT than the VMAT plan for a conventionally fractionated and relatively complex plan such as head and neck and endometrium cases.

Highlights

  • Intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) have become a standard modality for delivering highly conformal dose distributions as compared to 3D conformal techniques

  • The impact of an multileaf collimator (MLC) positioning error on IMRT/VMAT plans was studied by several authors by recalculating dose distribution in the treatment planning system (TPS) to reveal dose differences on target and critical structures [21,22]

  • We recently focused on the investigation of the effect of intentionally applying MLC positioning errors on patient plans, including SRS/stereotactic body radiotherapy (SBRT) and conventionally fractionated VMAT deliveries

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Summary

Introduction

Intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) have become a standard modality for delivering highly conformal dose distributions as compared to 3D conformal techniques. Both delivery modalities are capable to obtain highly conformal dose distribution into the target and steep dose gradients within the irradiated volume while minimizing doses in the organ at risk (OAR). The highly modulated dose distribution in VMAT plans can be achieved with the accurate operation of gantry rotation speed, the accuracy of multileaf collimator (MLC) leaves movement, and dose rate variation during radiation delivery [2]. Another study done by Oliver et al analyzed the MLC positioning error effect for VMAT plans and they concluded that the

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