Are simple IMRT beams more robust against MLC error? Exploring the impact of MLC errors on planar quality assurance and plan quality for different complexity beams.

Jiazhou Wang,Weigang Hu,Xiance Jin,Junchao Chen,Jiang Xie,Jiayuan Peng

doi:10.1120/jacmp.v17i3.6022

Abstract

This study investigated the impact of beam complexities on planar quality assurance and plan quality robustness by introducing MLC errors in intensity‐modulate radiation therapy. Forty patients' planar quality assurance (QA) plans were enrolled in this study, including 20 dynamic MLC (DMLC) IMRT plans and 20 static MLC (SMLC) IMRT plans. The total beam numbers were 150 and 160 for DMLC and SMLC, respectively. Six different magnitudes of MLC errors were introduced to these beams. Gamma pass rates were calculated by comparing error‐free fluence and error‐induced fluence. The plan quality variation was acquired by comparing PTV coverage. Eight complexity scores were calculated based on the beam fluence and the MLC sequence. The complexity scores include fractal dimension, monitor unit, modulation index, fluence map complexity, weighted average of field area, weighted average of field perimeter, and small aperture ratio (<5cm2 and<50 cm2). The Spearman's rank correlation coefficient was calculated to analyze the correlation between these scores and gamma pass rate and plan quality variation. For planar QA, the most significant complexity index was fractal dimension for DMLC (p=−0.40) and weighted segment area for SMLC (p=0.27) at low magnitude MLC error. For plan quality, the most significant complexity index was weighted segment perimeter for DMLC (p=0.56) and weighted segment area for SMLC (p=0.497) at low magnitude MLC error. The sensitivity of planar QA was weakly associated with the field complexity with low magnitude MLC error, but the plan quality robustness was associated with beam complexity. Plans with simple beams were more robust to MLC error.PACS number(s): 87.55

Highlights

148 Wang et al.: multileaf collimator (MLC) errors for different complexity beams distribution is assessed, using algorithms such as DTA,(2) DD, and gamma analysis.[3]
We explored the sensitivity of planar quality assurance and plan quality to MLC error with varying beam complexity in intensity-modulate radiation therapy (IMRT)
The gamma pass rate decreased with increased MLC leaf error for both dynamic MLC (DMLC) and static MLC (SMLC)

Summary

INTRODUCTION

148 Wang et al.: MLC errors for different complexity beams distribution is assessed, using algorithms such as DTA (distance to agreement),(2) DD (dose difference), and gamma analysis.[3]. Some studies pointed out that the complexity of individual beams might relate to delivery accuracy and QA metrics.[4,8] This means that complex beams with more irregularly shaped apertures and/or smaller segments tend to have lower pass rates in planar QA than simple beams using the same treatment planning system and delivery machine. Many studies have investigated the relation between the beam complexity and IMRT QA result, and a weak correlation between beam complexity and gamma pass rate was found.[13,14,15] These studies were all implemented with clinically commissioned treatment planning systems and clinically commissioned machines. The impact of MLC errors on different complexity beams and plans was analyzed

MATERIALS AND METHODS

RESULTS

Beams and plans complexity metrics

DISCUSSION

CONCLUSIONS