title: A two-dimensional liquid-filled ionization chamber array prototype for small-field verification: characterization and first clinical tests.
abstract: In this work we present the design, characterization and first clinical tests of an in-house developed two-dimensional liquid-filled ionization chamber prototype for the verification of small radiotherapy fields and treatments containing such small fields as in radiosurgery, which consists of 2 mm × 2 mm pixels arranged on a 16×8 rectangular grid. The ionization medium is isooctane. The characterization of the device included the study of depth, field-size and dose-rate dependences, which are sufficiently moderate for a good operation at therapy radiation levels. However, the detector presents an important anisotropic response, up to ≃ 12% for front versus near-lateral incidence, which can impact the verification of full treatments with different incidences. In such a case, an anisotropy correction factor can be applied. Output factors of small square fields measured with the device show a small systematic over-response, less than 1%, when compared to unshielded diode measurements. An IMRT radiosurgery treatment has been acquired with the liquid-filled ionization chamber device and compared with film dosimetry by using the gamma method, showing good agreement: over 99% passing rates for 1.2% and 1.2 mm for an incidence-per-incidence analysis; 100% passing rates for tolerances 1.8% and 1.8 mm when the whole treatment is analysed and the anisotropy correction factor is applied. The point dose verification for each incidence of the treatment performed with the liquid-filled ionization chamber agrees within 1% with a CC01 ionization chamber. This prototype has shown the utility of this kind of technology for the verification of small fields/treatments. Currently, a larger device covering a 5 cm × 5 cm area is under development.
authors: Hospital General de Valencia, ERESA, Servicio de Radiofísica, Valencia, Spain. lbrualla@eresa.com
authors: Luis
authors: L
authors: Brualla-González
authors: Faustino
authors: F
authors: Gómez
authors: Aurora
authors: A
authors: Vicedo
authors: Diego M
authors: DM
authors: González-Castaño
authors: Araceli
authors: A
authors: Gago-Arias
authors: Antonio
authors: A
authors: Pazos
authors: Martín
authors: M
authors: Zapata
authors: Joan V
authors: JV
authors: Roselló
authors: Juan
authors: J
authors: Pardo-Montero
mesh_terms: D016880:Anisotropy; D006801:Humans; D011874:Radiometry / Q000295:instrumentation*; D016634:Radiosurgery; D050397:Radiotherapy, Intensity-Modulated