Implementation of Aperture-Based Complexity Metrics of MLC Opening based on the IMRT Technique for Central Nervous System (CNS) and Breast cases

Document Type : Original Paper


1 Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia

2 Department of Radiation Oncology, Mochtar Riady Comprehensive Cancer Center (MRCCC) Siloam Hospital Semanggi, Jakarta



Background: Complexity metrics have been suggested to characterize treatment plans based on machine parameters such as multileaf collimator position. Several complexity metrics have been proposed and related to the IMRT quality assurance results. This study aims to evaluate aperture-based complexity metrics on multileaf collimator (MLC) openings used in clinical practice and establish a correlation between plan complexity and the gamma passing rate (GPR) for the IMRT plans.

Materials and methods: We implemented the aperture-based complexity metric on MLC openings of a clinical treatment plan for the sliding window IMRT technique in breast cancer and central nervous system (CNS) cancer patients. The modulation complexity score (MCS), the edge area metric (EAM), the converted area metric (CAM), the circumference/area (CPA), and the ratio monitor unit MU/Gy are evaluated in this study. The complexity score was calculated using Matlab. The GPR value was assessed for its correlation to complexity metrics. The 2D ionization chamber array MatriXX Evolution was used for dose verification. The measured and calculated 2D dose distributions were analyzed with the OmniPro-I'mRT analysis software and were subsequently compared using the gamma index parameter of 3%/3 mm and 3%/2 mm with a 10% threshold. The correlation between the calculated complexity score and the gamma pass rate is analyzed using SPSS.

Results: The complexity score calculated by MCS, EAM, CAM, CPA, and MU/Gy shows breast plan is more complex than the CNS plan. The results of the correlation test of the complexity metric and GPR show that only the EAM metric shows a good correlation with GPR for both cases. Correlation coefficient values for CNS cases are -0.918 (3%/3 mm) and -0.864 (3%/2 mm), while for breast cases the correlation coefficient values are -0.983 (3%/3 mm) and -0.961 (3%/2 mm).


Main Subjects

Articles in Press, Accepted Manuscript
Available Online from 15 March 2023
  • Receive Date: 09 December 2022
  • Revise Date: 28 September 2023
  • Accept Date: 15 March 2023
  • First Publish Date: 15 March 2023