System for dose audit for external radiation therapy based on EPR dosimetry with Lithium Formate

摘要: Radiation therapy is an important method to treat cancer with the aim deliver as high doses reasonably achievable tumor while protecting surrounding healthy tissue and organs at risk, OARs. Therefore, it essential have accuracy in dose delivered clinically quality assurances are required. In meantime, radiation techniques becoming more advanced complex, introducing a significant risk of random systematic errors that needs be investigated. Hence, need independent verifications has increased. The purpose present work design create mailed audit system for external evaluation water relevant points phantom, including influences from whole treatment chain, computed tomography, CT, scanning, contouring structures, planning delivery.The measurements were performed using anthropomorphic Polymethyl methacrylate, PMMA, phantom designed head-and-neck region containing inserts corresponding tumour, salivary glands medulla made PMMA easily distinguishable surroundings contouring. Inhomogeneities both Teflon, spinal cord, air also included. Pellet shaped electron paramagnetic resonance, EPR, dosimeters lithium formate diameter 4.5 mm height 5 measurements. can placed various positions different structures tubes analyzed spectrometer.In order test precision EPR dosimetry method, three blind tests simultaneously ionization chamber comparison absorbed doses. For measurement, was CT scanned twice Siemens scan GE (General Electric)) Hounsfield Units, HU, distributions. target OARs contoured system, TPS, (Varian, Eclipse) dynamic Intensity modulated therapy, IMRT, plan created. consisted seven coplanar 6 MV fields giving Gy Varian, Clinac iX accelerator. determined locations: target, one each parotis, cavity. signal compared planned Also, measured reconstructed volumes compared.The obtained agreed results within 1% well below calculated uncertainties (1 SD) distributions not affected by any spread HU had agreement 0.5% between studies. 4% all except This deviation covered standard uncertainty. However, does fall two deviations, confidence interval 95%. Also 2.5% smaller 5% larger structures.Repeating measurement chain other dosimeter batches required or point higher precision. A conclusion this showed promising initial chain.