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Title: Breast in vivo dosimetry by a portal ionization chamber

Abstract

This work reports a practical method for the determination of the in vivo breast middle dose value, D{sub m}, on the beam central axis, using a signal S{sub t}, obtained by a small thimble ion chamber positioned at the center of the electronic portal imaging device, and irradiated by the x-ray beam transmitted through the patient. The use of a stable ion chamber reduces many of the disadvantages associated with the use of diodes as their periodic recalibration and positioning is time consuming. The method makes use of a set of correlation functions obtained by the ratios S{sub t}/D{sub m}, determined by irradiating cylindrical water phantoms with different diameters. The method proposed here is based on the determination of the water-equivalent thickness of the patient, along the beam central axis, by the treatment planning system that makes use of the electron densities obtained by a computed tomography scanner. The method has been applied for the breast in vivo dosimetry of ten patients treated with a manual intensity modulation with four asymmetric beams. In particular, two tangential rectangular fields were first delivered, thereafter a fraction of the dose (typically less than 10%) was delivered with two multi leaf-shaped beams which includedmore » only the mammarian tissue. Only the two rectangular fields were tested and for every checked field five measurements were carried out. Applying a continuous quality assurance program based on the tests of patient setup, machine settings and dose planning, the proposed method is able to verify agreements between the computed dose D{sub m,TPS} and the in vivo dose value D{sub m}, within 4%.« less

Authors:
; ; ; ; ; ; ; ; ;  [1]
  1. U.O. di Fisica Sanitaria - Centro di Ricerca ad Alta Tecnologia nelle Scienze Biomediche dell'Universita Cattolica S. Cuore, Campobasso and Istituto di Fisica - Universita Cattolica del S. Cuore, Rome (Italy) and U.O. di Radioterapia - Centro di Ricerca ad Alta Tecnologia nelle Scienze Biomediche dell'Universita Cattolica S. Cuore, Campobasso and U.O. di Fisica Sanitaria- Centro di Ricerca ad Alta Tecnologia nelle Scienze Biomediche dell'Universita Cattolica S. Cuore, Campobasso and Istituto di Fisica - Universita Cattolica del S. Cuore, Rome (Italy)
Publication Date:
OSTI Identifier:
20951097
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 3; Other Information: DOI: 10.1118/1.2426401; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; BEAMS; COMPUTERIZED TOMOGRAPHY; DOSIMETRY; ELECTRON DENSITY; IN VIVO; IONIZATION CHAMBERS; IRRADIATION; MAMMARY GLANDS; PATIENTS; PHANTOMS; PLANNING; QUALITY ASSURANCE; RADIATION DOSES; RADIOTHERAPY

Citation Formats

Grimaldi, Luca, D'Onofrio, Guido, Cilla, Savino, Fidanzio, Andrea, Stimato, Gerardina, Azario, Luigi, Deodato, Francesco, Macchia, Gabriella, Morganti, Alessio, and Piermattei, Angelo. Breast in vivo dosimetry by a portal ionization chamber. United States: N. p., 2007. Web. doi:10.1118/1.2426401.
Grimaldi, Luca, D'Onofrio, Guido, Cilla, Savino, Fidanzio, Andrea, Stimato, Gerardina, Azario, Luigi, Deodato, Francesco, Macchia, Gabriella, Morganti, Alessio, & Piermattei, Angelo. Breast in vivo dosimetry by a portal ionization chamber. United States. doi:10.1118/1.2426401.
Grimaldi, Luca, D'Onofrio, Guido, Cilla, Savino, Fidanzio, Andrea, Stimato, Gerardina, Azario, Luigi, Deodato, Francesco, Macchia, Gabriella, Morganti, Alessio, and Piermattei, Angelo. Thu . "Breast in vivo dosimetry by a portal ionization chamber". United States. doi:10.1118/1.2426401.
@article{osti_20951097,
title = {Breast in vivo dosimetry by a portal ionization chamber},
author = {Grimaldi, Luca and D'Onofrio, Guido and Cilla, Savino and Fidanzio, Andrea and Stimato, Gerardina and Azario, Luigi and Deodato, Francesco and Macchia, Gabriella and Morganti, Alessio and Piermattei, Angelo},
abstractNote = {This work reports a practical method for the determination of the in vivo breast middle dose value, D{sub m}, on the beam central axis, using a signal S{sub t}, obtained by a small thimble ion chamber positioned at the center of the electronic portal imaging device, and irradiated by the x-ray beam transmitted through the patient. The use of a stable ion chamber reduces many of the disadvantages associated with the use of diodes as their periodic recalibration and positioning is time consuming. The method makes use of a set of correlation functions obtained by the ratios S{sub t}/D{sub m}, determined by irradiating cylindrical water phantoms with different diameters. The method proposed here is based on the determination of the water-equivalent thickness of the patient, along the beam central axis, by the treatment planning system that makes use of the electron densities obtained by a computed tomography scanner. The method has been applied for the breast in vivo dosimetry of ten patients treated with a manual intensity modulation with four asymmetric beams. In particular, two tangential rectangular fields were first delivered, thereafter a fraction of the dose (typically less than 10%) was delivered with two multi leaf-shaped beams which included only the mammarian tissue. Only the two rectangular fields were tested and for every checked field five measurements were carried out. Applying a continuous quality assurance program based on the tests of patient setup, machine settings and dose planning, the proposed method is able to verify agreements between the computed dose D{sub m,TPS} and the in vivo dose value D{sub m}, within 4%.},
doi = {10.1118/1.2426401},
journal = {Medical Physics},
number = 3,
volume = 34,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}