title: Three-dimensional radiochromic film dosimetry for volumetric modulated arc therapy using a spiral water phantom.
abstract: We validated 3D radiochromic film dosimetry for volumetric modulated arc therapy (VMAT) using a newly developed spiral water phantom. The phantom consists of a main body and an insert box, each of which has an acrylic wall thickness of 3 mm and is filled with water. The insert box includes a spiral film box used for dose-distribution measurement, and a film holder for positioning a radiochromic film. The film holder has two parallel walls whose facing inner surfaces are equipped with spiral grooves in a mirrored configuration. The film is inserted into the spiral grooves by its side edges and runs along them to be positioned on a spiral plane. Dose calculation was performed by applying clinical VMAT plans to the spiral water phantom using a commercial Monte Carlo-based treatment-planning system, Monaco, whereas dose was measured by delivering the VMAT beams to the phantom. The calculated dose distributions were resampled on the spiral plane, and the dose distributions recorded on the film were scanned. Comparisons between the calculated and measured dose distributions yielded an average gamma-index pass rate of 87.0% (range, 91.2-84.6%) in nine prostate VMAT plans under 3 mm/3% criteria with a dose-calculation grid size of 2 mm. The pass rates were increased beyond 90% (average, 91.1%; range, 90.1-92.0%) when the dose-calculation grid size was decreased to 1 mm. We have confirmed that 3D radiochromic film dosimetry using the spiral water phantom is a simple and cost-effective approach to VMAT dose verification.
authors.affiliation: Department of Radiology, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya City, Hyogo, 663-8501, Japan.
authors.forename: Masao
authors.initials: M
authors.lastname: Tanooka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Doi
authors.forename: Hideharu
authors.initials: H
authors.lastname: Miura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Inoue
authors.forename: Yasue
authors.initials: Y
authors.lastname: Niwa
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takada
authors.forename: Masayuki
authors.initials: M
authors.lastname: Fujiwara
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Sakai
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Norihiko
authors.initials: N
authors.lastname: Kamikonya
authors.forename: Shozo
authors.initials: S
authors.lastname: Hirota
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005373:Film Dosimetry / Q000295:instrumentation* / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014867:Water
chemical_list: D014867:Water
keywords: QA; VMAT; film dosimetry; radiochromic film; spiral phantom; spiral water phantom