title: Commissioning of 6 MV medical linac for dynamic MLC-based IMRT on Monte Carlo code GEANT4.
abstract: 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 cm(2) field and the measured dose profile for a 35 × 35 cm(2) 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.
authors: Radiation Oncology Division, National Cancer Center Hospital, Tokyo, 104-0045, Japan, hiokamot@ncc.go.jp.
authors: Hiroyuki
authors: H
authors: Okamoto
authors: Yukio
authors: Y
authors: Fujita
authors: Kyoko
authors: K
authors: Sakama
authors: Hidetoshi
authors: H
authors: Saitoh
authors: Tatsuaki
authors: T
authors: Kanai
authors: Jun
authors: J
authors: Itami
authors: Toshiyuki
authors: T
authors: Kohno
mesh_terms: D009010:Monte Carlo Method; D010315:Particle Accelerators; D011874:Radiometry; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation*