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


Introduction: Complexity metrics have been suggested to characterize treatment plans based on machine parameters such as multileaf collimator (MLC) position. Several complexity metrics have been proposed and related to the Intensity-modulated radiation therapy (IMRT) quality assurance results. This study aims to evaluate aperture-based complexity metrics on MLC openings used in clinicaland establish a correlation between plan complexity and the gamma passing rate (GPR) for the IMRT plans.
Material and Methods: We implemented the aperture-based complexity metric on MLC openings of the IMRT treatment plan for breast  and central nervous system (CNS) cases . 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 MatriXX Evolution was used for dose verification. The dose distribution was  analyzed using the OmniPro-I'mRT program  and the gamma index was assessed using two criteria: 3%/3 mm and 3%/2 mm. The correlation between the calculated complexity score and the GPR  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.
Conclusion: EAM strongly correlates with the gamma pass rate. The MCS, CAM, CPA, and MU/Gy have a weak correlation with the GPR.


Main Subjects



  1. Elith C, Dempsey SE, Findlay N, Warren-Forward HM. An introduction to the intensity-modulated radiation therapy (IMRT) techniques, tomotherapy, and VMAT. Journal of Medical Imaging and Radiation Sciences. 2011 Mar 1;42(1):37-43. doi: 10.1016/j.jmir.2010.11.005.
  2. Rajasekaran D, Jeevanandam P, Sukumar P, Ranganathan A, Johnjothi S, Nagarajan V. A study on the correlation between plan complexity and gamma index analysis in patient specific quality assurance of volumetric modulated arc therapy. Reports of Practical Oncology and Radiotherapy. 2015;20(1):57-65. doi: 10.1016/j.rpor.2014.08.006.
  3. Götstedt J, Karlsson Hauer A, Bäck A. Development and evaluation of aperture‐based complexity metrics using film and EPID measurements of static MLC openings. Medical physics. 2015 Jul;42(7):3911-21. doi: 10.1118/1.4921733.
  4. Wang Y, Pang X, Feng L, Wang H, Bai Y. Correlation between gamma passing rate and complexity of IMRT plan due to MLC position errors. Physica Medica. 2018 Mar 1;47:112-20. doi: 10.1016/j.ejmp.2018.03.003.
  5. Moran JM, Dempsey M, Eisbruch A, Fraass BA, Galvin JM, Ibbott GS, et al. Safety considerations for IMRT: executive summary. Medical physics. 2011 Sep;38(9):5067-72. doi: 10.1016/j.prro.2011.04.008.
  6. Bäck A, Larsson A, Götstedt J, Hauer AK. EP-1595: Impact of different dose calculation algorithms on aperture-based complexity metric evaluations. Radiotherapy and Oncology. 2016;1(119):S741-2.
  7. McNiven AL, Sharpe MB, Purdie TG. A new metric for assessing IMRT modulation complexity and plan deliverability. Medical physics. 2010 Feb;37(2):505-15. doi: 10.1118/1.3276775.
  8. Jubbier ON, Abdullah SS, Alabedi HH, Alazawy NM, Al-Musawi MJ. The effect of modulation complexity score (MCS) on the IMRT treatment planning delivery accuracy. InJournal of physics: conference series 2021 Mar 1 (Vol. 1829, No. 1, p. 012017). IOP Publishing. doi: 10.1088/1742-6596/1829/1/012017.
  9. Svensson E, Bäck A, Hauer AK. Evaluation of complexity and deliverability of IMRT-treatment plans. Göteborg: The Sahlgrenska Academy. 2011 Jun.
  10. Masi L, Doro R, Favuzza V, Cipressi S, Livi L. Impact of plan parameters on the dosimetric accuracy of volumetric modulated arc therapy. Medical physics. 2013 Jul;40(7):071718. doi: 10.1118/1.4810969.
  11. McGarry CK, Chinneck CD, O'Toole MM, O'Sullivan JM, Prise KM, Hounsell AR. Assessing software upgrades, plan properties and patient geometry using intensity modulated radiation therapy (IMRT) complexity metrics. Medical physics. 2011 Apr;38(4):2027-34. doi: 10.1118/1.3562897.
  12. Tonigan JR. Evaluation of intensity modulated radiation therapy (IMRT) delivery error due to IMRT treatment plan complexity and improperly matched dosimetry data. Available:
  13. Glenn MC, Hernandez V, Saez J, Followill DS, Howell RM, Pollard-Larkin JM, et al. Treatment plan complexity does not predict IROC Houston anthropomorphic head and neck phantom performance. Physics in Medicine & Biology. 2018 Oct 17;63(20):205015. doi: 10.1088/1361-6560/aae29e.
  14. Götstedt J, Bäck A. Edge area metric complexity scoring of volumetric modulated arc therapy plans. Physics and Imaging in Radiation Oncology. 2021 Jan 1;17:124-9. doi: 10.1016/j.phro.2021.02.002.
  15. Chung JB, Kim JS, Ha SW, Ye SJ. Statistical analysis of IMRT dosimetry quality assurance measurements for local delivery guideline. Radiation Oncology. 2011 Dec;6:1-8. doi: 10.1186/1748-717X-6-27.