Ion recombination for ionization chamber dosimetry in a helical tomotherapy unit

Medical Physics
Hugo PalmansS Vynckier

Abstract

Ion recombination for ionization chambers in pulsed high-energy photon beams is a well-studied phenomenon. Despite this, the correction for ion recombination is often determined inaccurately due to the inappropriate combination of using a high polarizing voltage and the simple two-voltage method. An additional complication arises in new treatment modalities such as IMRT and tomotherapy, where the dosimetry of a superposition of many constituting fields becomes more relevant than of single static fields. For these treatment modalities, the irradiation of the ion chamber geometry can be instantaneously inhomogeneous and time dependent. This article presents a study of ion recombination in ionization chambers used for dosimetry in a helical tomotherapy beam. Models are presented for studying the recombination correction factors in a continuous beam, in pulsed large and small fields, and in helical fields. Measurements using Exradin A1SL, NE2571, and NE2611 type chambers and Monte Carlo simulations using PENELOPE are performed in support of these models. Initial recombination and charge multiplication are found to be the same in 60Co and in the pulsed high-energy photon beam for the chambers and operating voltages used in this stud...Continue Reading

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Feb 10, 2006·Physics in Medicine and Biology·Hugo PalmansAndrzej Kacperek
Apr 4, 2008·Physics in Medicine and Biology·E SterpinS Vynckier
Dec 17, 2008·Medical Physics·R AlfonsoS Vatnitsky

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Citations

Jan 10, 2012·Medical Physics·Eunah ChungJan Seuntjens
Oct 4, 2011·Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology·Michele ZeverinoGianni Taccini
Jul 3, 2016·Medical Physics·S RossommeH Palmans
Sep 8, 2012·Journal of Applied Clinical Medical Physics·Yuenan WangJoseph Y Ting
Nov 15, 2012·Journal of Applied Clinical Medical Physics·Stephen F KryDavid S Followill
Nov 14, 2018·Medical Physics·Simona Giordanengo, Hugo Palmans
Oct 12, 2019·Medical Physics·Maria do Carmo LopesMiguel Capela
Aug 1, 2019·Physics in Medicine and Biology·S RossommeH Palmans
Mar 4, 2014·Physics in Medicine and Biology·S J ThomasUNKNOWN IPEM Working Party

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