EPR imaging of magnetic field effects on radiation dose distributions around millimeter-size air cavities.
作者： Sebastian Höfel , Michael K Fix , Felix Zwicker , Edmond Sterpin , Malte Drescher
关键词: Paramagnetism 、 Dosimetry 、 Magnetic field 、 Imaging phantom 、 Fused quartz 、 Electron 、 Irradiation 、 Ionizing radiation 、 Materials science 、 Molecular physics
摘要: New hybrid radiotherapy treatment systems combining an MRI scanner with a source of ionizing radiation are being introduced in the clinic. The strong magnetic fields considerably affect dose distributions, especially at tissue-air interfaces due to electron return effect (ERE). Experimental investigation ERE within sub-millimeter thick surface layer is still highly challenging. In present work, we examine and quantify field induced perturbations distributions 0.5 mm surrounding millimeter-size air cavities by applying paramagnetic resonance imaging (EPRI). Air-filled fused quartz tubes (inner diameter 3 or 4 mm) mimic small serve as model systems. were irradiated inside PMMA phantom 6 MV photon beam. irradiations performed presence absence transverse, providing strength 1.0 Tesla. spatial defects subsequently determined field-swept echo-detected EPRI then converted relative distributions. transverse leads considerable local enhancements reductions (up 35%) respect mean tubes. experimentally good quantitative agreement Monte Carlo transport simulations. results this work demonstrate feasibility measure dosimeter-air interface.
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