Commissioning of 6 MV medical linac for dynamic MLC-based IMRT on Monte Carlo code GEANT4

Hiroyuki Okamoto, Yukio Fujita, Kyoko Sakama, Hidetoshi Saitoh, Tatsuaki Kanai, Jun Itami, Toshiyuki Kohno

    Research output: Contribution to journalArticlepeer-review

    5 Citations (Scopus)


    Monte Carlo simulation is the most accurate tool for calculating dose distributions. In particular, the Electron Gamma shower computer code has been widely used for multi-purpose research in radiotherapy, but Monte Carlo GEANT4 (GEometry ANd Tracking) is rare for radiotherapy with photon beams and needs to be verified further under various irradiation conditions, particularly multi-leaf collimator-based intensity-modulated radiation therapy (MLC-based IMRT). In this study, GEANT4 was used for modeling of a 6 MV linac for dynamic MLC-based IMRT. To verify the modeling of our linac, we compared the calculated data with the measured depth-dose for a 10 × 10 cm2 field and the measured dose profile for a 35 × 35 cm2 field. Moreover, 120 MLCs were modeled on the GEANT4. Five tests of MLC modeling were performed: (I) MLC transmission, (II) MLC transmission profile including intra- and inter-leaf leakage, (III) tongue-and-groove leakage, (IV) a simple field with different field sizes by use of MLC and (V) a dynamic MLC-based IMRT field. For all tests, the calculations were compared with measurements of an ionization chamber and radiographic film. The calculations agreed with the measurements: MLC transmissions by calculations and measurements were 1.76 ± 0.01 and 1.87 ± 0.01 %, respectively. In gamma evaluation method (3 %/3 mm), the pass rates of the (IV) and (V) tests were 98.5 and 97.0 %, respectively. Furthermore, tongue-and-groove leakage could be calculated by GEANT4, and it agreed with the film measurements. The procedure of commissioning of dynamic MLC-based IMRT for GEANT4 is proposed in this study.

    Original languageEnglish
    Pages (from-to)246-253
    Number of pages8
    JournalRadiological Physics and Technology
    Issue number2
    Publication statusPublished - 2014 Jul


    • Commissioning
    • GEANT4
    • IMRT
    • MLC
    • Monte Carlo simulation
    • Tongue-and-groove

    ASJC Scopus subject areas

    • Radiation
    • Physical Therapy, Sports Therapy and Rehabilitation
    • Radiology Nuclear Medicine and imaging


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