title: Preliminary study on the use of an inhomogeneous anthropomorphic Fricke gel phantom and 3D magnetic resonance dosimetry for verification of IMRT treatment plans.
abstract: An inhomogeneous anthropomorphic phantom of the human thorax including lungs and spine was developed for verification of three-dimensional (3D) intensity-modulated radiotherapy (IMRT). The phantom and spinal cord were filled with undiluted Fricke gel, whereas the lungs were filled with a special low-density Fricke gel. Based on a computed tomography scan of the phantom, an intensity-modulated stereotactic radiotherapy plan for a bronchial carcinoma was calculated using an inverse planning system (KonRad, DKFZ Heidelberg, Germany). The plan consisted of seven beams delivered in a step and shoot technique out of 67 sub-fields. Immediately after irradiation 3D magnetic resonance (MR) imaging of the phantom was performed using a special pulse sequence for T1 relaxometry. From the MR image data maps of the longitudinal relaxation rate R1 = 1/T1 were calculated. The R1 maps were converted to dose-proportional image data and compared to planning data. Measurement and planning show good agreement in regions of standard Fricke gel with an average deviation below 5%. In regions of the low-density Fricke gel, deviations are higher due to a decreased signal-to-noise ratio in the MR measurement. In these areas also a different sensitivity of the dose response was observed as compared to standard Fricke gel. The inhomogeneous thorax phantom has proven to be a useful pre-clinical tool for 3D methodical verifications.
authors: Department of Radiotherapy, University Hospital Regensburg, Germany.
authors: F
authors: F
authors: Gum
authors: J
authors: J
authors: Scherer
authors: L
authors: L
authors: Bogner
authors: M
authors: M
authors: Solleder
authors: B
authors: B
authors: Rhein
authors: M
authors: M
authors: Bock
mesh_terms: D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D019047:Phantoms, Imaging; D011874:Radiometry / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D013116:Spinal Cord / Q000528:radiation effects; D014057:Tomography, X-Ray Computed