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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">Assessment of the setup dependence of detector response functions for mega-voltage linear accelerators</title><author><name sortKey="Fox, Christopher" sort="Fox, Christopher" uniqKey="Fox C" first="Christopher" last="Fox">Christopher Fox</name></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">20229856</idno><idno type="pmc">2814833</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2814833</idno><idno type="RBID">PMC:2814833</idno><idno type="doi">10.1118/1.3284529</idno><date when="2010">2010</date><idno type="wicri:Area/Pmc/Corpus">000072</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">000072</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">Assessment of the setup dependence of detector response functions for mega-voltage linear accelerators</title><author><name sortKey="Fox, Christopher" sort="Fox, Christopher" uniqKey="Fox C" first="Christopher" last="Fox">Christopher Fox</name></author></analytic><series><title level="j">Medical Physics</title><idno type="ISSN">0094-2405</idno><idno type="eISSN">0094-2405</idno><imprint><date when="2010">2010</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><p><bold>Purpose:</bold> Accurate modeling of beam profiles is important for precise treatment planning dosimetry. Calculated beam profiles need to precisely replicate profiles measured during machine commissioning. Finite detector size introduces perturbations into the measured profiles, which, in turn, impact the resulting modeled profiles. The authors investigate a method for extracting the unperturbed beam profiles from those measured during linear accelerator commissioning.</p><p><bold>Methods:</bold> In-plane and cross-plane data were collected for an Elekta Synergy linac at 6 MV using ionization chambers of volume 0.01, 0.04, 0.13, and 0.65 cm<sup>3</sup> and a diode of surface area 0.64 mm<sup>2</sup>. The detectors were orientated with the stem perpendicular to the beam and pointing away from the gantry. Profiles were measured for a 10×10 cm<sup>2</sup> field at depths ranging from 0.8 to 25.0 cm and SSDs from 90 to 110 cm. Shaping parameters of a Gaussian response function were obtained relative to the Edge detector. The Gaussian function was deconvolved from the measured ionization chamber data. The Edge detector profile was taken as an approximation to the true profile, to which deconvolved data were compared. Data were also collected with CC13 and Edge detectors for additional fields and energies on an Elekta Synergy, Varian Trilogy, and Siemens Oncor linear accelerator and response functions obtained. Response functions were compared as a function of depth, SSD, and detector scan direction. Variations in the shaping parameter were introduced and the effect on the resulting deconvolution profiles assessed.</p><p><bold>Results:</bold> Up to 10% setup dependence in the Gaussian shaping parameter occurred, for each detector for a particular plane. This translated to less than a ±0.7 mm variation in the 80%–20% penumbral width. For large volume ionization chambers such as the FC65 Farmer type, where the cavity length to diameter ratio is far from 1, the scan direction produced up to a 40% difference in the shaping parameter between in-plane and cross-plane measurements. This is primarily due to the directional difference in penumbral width measured by the FC65 chamber, which can more than double in profiles obtained with the detector stem parallel compared to perpendicular to the scan direction. For the more symmetric CC13 chamber the variation was only 3% between in-plane and cross-plane measurements.</p><p><bold>Conclusions:</bold> The authors have shown that the detector response varies with detector type, depth, SSD, and detector scan direction. In-plane vs cross-plane scanning can require calculation of a direction dependent response function. The effect of a 10% overall variation in the response function, for an ionization chamber, translates to a small deviation in the penumbra from that of the Edge detector measured profile when deconvolved. Due to the uncertainties introduced by deconvolution the Edge detector would be preferable in obtaining an approximation of the true profile, particularly for field sizes where the energy dependence of the diode can be neglected. However, an averaged response function could be utilized to provide a good approximation of the true profile for large ionization chambers and for larger fields for which diode detectors are not recommended.</p></div></front></TEI><pmc article-type="research-article"><pmc-comment>The publisher of this article does not allow downloading of the full text in XML form.</pmc-comment>
<front><journal-meta><journal-id journal-id-type="nlm-ta">Med Phys</journal-id><journal-title-group><journal-title>Medical Physics</journal-title></journal-title-group><issn pub-type="ppub">0094-2405</issn><issn pub-type="epub">0094-2405</issn><publisher><publisher-name>American Association of Physicists in Medicine</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="pmid">20229856</article-id><article-id pub-id-type="pmc">2814833</article-id><article-id pub-id-type="publisher-id">023002MPH</article-id><article-id pub-id-type="doi">10.1118/1.3284529</article-id><article-categories><subj-group subj-group-type="heading"><subject>Radiation Therapy Physics</subject></subj-group></article-categories><title-group><article-title>Assessment of the setup dependence of detector response functions for mega-voltage linear accelerators</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Fox</surname><given-names>Christopher</given-names></name><xref ref-type="author-notes" rid="n1">a)</xref></contrib><aff>Sun Nuclear Inc., 425-A Pineda Court, Melbourne, Florida 32940 and Department of Radiation Oncology, University of Florida, P.O. Box 100385, Gainesville, Florida 32610-0385</aff></contrib-group><contrib-group><contrib contrib-type="author"><name><surname>Simon</surname><given-names>Tom</given-names></name></contrib><aff>NRE, 202 Nuclear Science Building, University of Florida, P.O. Box 118300, Gainesville, Florida 32611-8300 and Sun Nuclear Inc., 425-A Pineda Court, Melbourne, Florida 32940</aff></contrib-group><contrib-group><contrib contrib-type="author"><name><surname>Simon</surname><given-names>Bill</given-names></name></contrib><aff>Sun Nuclear Inc., 425-A Pineda Court, Melbourne, Florida 32940</aff></contrib-group><contrib-group><contrib contrib-type="author"><name><surname>Dempsey</surname><given-names>James F.</given-names></name></contrib><aff>ViewRay Inc., 2 Thermo Fisher Way, Oakwood Village, Ohio 44146</aff></contrib-group><contrib-group><contrib contrib-type="author"><name><surname>Kahler</surname><given-names>Darren</given-names></name></contrib><contrib contrib-type="author"><name><surname>Palta</surname><given-names>Jatinder R.</given-names></name></contrib><contrib contrib-type="author"><name><surname>Liu</surname><given-names>Chihray</given-names></name></contrib><contrib contrib-type="author"><name><surname>Yan</surname><given-names>Guanghua</given-names></name></contrib><aff>Department of Radiation Oncology, University of Florida, P.O. Box 100385, Gainesville, Florida 32610-0385</aff></contrib-group><author-notes><fn id="n1"><label>a)</label><p>Author to whom correspondence should be addressed. Electronic mail: <email>cfox3@tulane.edu</email>; Present address: Department of Radiation Oncology, Tulane University, 1415 Tulane Ave., HC65, New Orleans, Louisiana 70112.</p></fn></author-notes><pub-date pub-type="ppub"><month>2</month><year>2010</year></pub-date><pub-date pub-type="epub"><day>07</day><month>1</month><year>2010</year></pub-date><volume>37</volume><issue>2</issue><fpage>477</fpage><lpage>484</lpage><history><date date-type="received"><day>16</day><month>3</month><year>2009</year></date><date date-type="rev-recd"><day>07</day><month>12</month><year>2009</year></date><date date-type="accepted"><day>08</day><month>12</month><year>2009</year></date></history><permissions><copyright-statement>Copyright © 2010 American Association of Physicists in Medicine</copyright-statement><copyright-year>2010</copyright-year><copyright-holder>American Association of Physicists in Medicine</copyright-holder></permissions><abstract><p><bold>Purpose:</bold> Accurate modeling of beam profiles is important for precise treatment planning dosimetry. Calculated beam profiles need to precisely replicate profiles measured during machine commissioning. Finite detector size introduces perturbations into the measured profiles, which, in turn, impact the resulting modeled profiles. The authors investigate a method for extracting the unperturbed beam profiles from those measured during linear accelerator commissioning.</p><p><bold>Methods:</bold> In-plane and cross-plane data were collected for an Elekta Synergy linac at 6 MV using ionization chambers of volume 0.01, 0.04, 0.13, and 0.65 cm<sup>3</sup> and a diode of surface area 0.64 mm<sup>2</sup>. The detectors were orientated with the stem perpendicular to the beam and pointing away from the gantry. Profiles were measured for a 10×10 cm<sup>2</sup> field at depths ranging from 0.8 to 25.0 cm and SSDs from 90 to 110 cm. Shaping parameters of a Gaussian response function were obtained relative to the Edge detector. The Gaussian function was deconvolved from the measured ionization chamber data. The Edge detector profile was taken as an approximation to the true profile, to which deconvolved data were compared. Data were also collected with CC13 and Edge detectors for additional fields and energies on an Elekta Synergy, Varian Trilogy, and Siemens Oncor linear accelerator and response functions obtained. Response functions were compared as a function of depth, SSD, and detector scan direction. Variations in the shaping parameter were introduced and the effect on the resulting deconvolution profiles assessed.</p><p><bold>Results:</bold> Up to 10% setup dependence in the Gaussian shaping parameter occurred, for each detector for a particular plane. This translated to less than a ±0.7 mm variation in the 80%–20% penumbral width. For large volume ionization chambers such as the FC65 Farmer type, where the cavity length to diameter ratio is far from 1, the scan direction produced up to a 40% difference in the shaping parameter between in-plane and cross-plane measurements. This is primarily due to the directional difference in penumbral width measured by the FC65 chamber, which can more than double in profiles obtained with the detector stem parallel compared to perpendicular to the scan direction. For the more symmetric CC13 chamber the variation was only 3% between in-plane and cross-plane measurements.</p><p><bold>Conclusions:</bold> The authors have shown that the detector response varies with detector type, depth, SSD, and detector scan direction. In-plane vs cross-plane scanning can require calculation of a direction dependent response function. The effect of a 10% overall variation in the response function, for an ionization chamber, translates to a small deviation in the penumbra from that of the Edge detector measured profile when deconvolved. Due to the uncertainties introduced by deconvolution the Edge detector would be preferable in obtaining an approximation of the true profile, particularly for field sizes where the energy dependence of the diode can be neglected. However, an averaged response function could be utilized to provide a good approximation of the true profile for large ionization chambers and for larger fields for which diode detectors are not recommended.</p></abstract><custom-meta-group><custom-meta><meta-name>CCC information</meta-name><meta-value>0094-2405/2010/37(2)/477/8/$30.00</meta-value></custom-meta><custom-meta><meta-name>sisac</meta-name><meta-value>0094-2405()37:2L.477;1</meta-value></custom-meta><custom-meta><meta-name>edcode</meta-name><meta-value>09-208R2</meta-value></custom-meta><custom-meta><meta-name>aipkey</meta-name><meta-value>1.3284529</meta-value></custom-meta><custom-meta><meta-name>spin</meta-name><meta-value><named-content content-type="el-docanal"><named-content content-type="el-pacs"><named-content content-type="att-pacsyr">2010</named-content><named-content content-type="el-pacscode">8753Bn</named-content><named-content content-type="el-pacscode">8753Jw</named-content><named-content content-type="el-pacscode">8756bd</named-content><named-content content-type="el-pacscode">2940Cs</named-content><named-content content-type="el-pacscode">2920Ej</named-content></named-content></named-content><named-content content-type="el-jouidx"><named-content content-type="el-country">US</named-content><named-content content-type="el-totalidx">6</named-content><named-content content-type="el-addidx">biomedical equipment</named-content><named-content content-type="el-addidx">dosimeters</named-content><named-content content-type="el-addidx">dosimetry</named-content><named-content content-type="el-addidx">ionisation chambers</named-content><named-content content-type="el-addidx">linear accelerators</named-content><named-content content-type="el-addidx">radiation therapy</named-content></named-content></meta-value></custom-meta></custom-meta-group></article-meta></front></pmc></record>Pour manipuler ce document sous Unix (Dilib)
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