Two self-referencing methods for the measurement of beam spot position
Purpose: Two quantitative methods of measuring electron beam spot position with respect to the collimator axis of rotation (CAOR) are described. Methods: Method 1 uses a cylindrical ion chamber (IC) mounted on a jig corotational with the collimator making the relationship among the chamber, jaws, an...
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| creator | Nyiri, Balazs J. Smale, Jason R. Gerig, Lee H. |
| description | Purpose:
Two quantitative methods of measuring electron beam spot position with respect to the collimator axis of rotation (CAOR) are described.
Methods:
Method 1 uses a cylindrical ion chamber (IC) mounted on a jig corotational with the collimator making the relationship among the chamber, jaws, and CAOR fixed and independent of collimator angle. A jaw parallel to the IC axis is set to zero and the IC position adjusted so that the IC signal is approximately 50% of the open field value, providing a large dose gradient in the region of the IC. The cGy/MU value is measured as a function of collimator rotation, e.g., every 30°. If the beam spot does not lie on the CAOR, the signal from the ion chamber will vary with collimator rotation. Based on a measured spatial sensitivity, the distance of the beam spot from the CAOR can be calculated from the IC signal variation with rotation. The 2nd method is image based. Two stainless steel rods, 3 mm in diameter, are mounted to a jig attached to the Linac collimator. The rods, offset from the CAOR, lay in different planes normal to the CAOR, one at 158 cm SSD and the other at 70 cm SSD. As the collimator rotates the rods move tangent along an envelope circle, the centers of which are on the CAOR in their respective planes. Three images, each at a different collimator rotation, containing the shadows of both rods, are acquired on the Linac EPID. At each angle the shadow of the rods on the EPID defines lines tangent to the projection of the envelope circles. From these the authors determine the projected centers of the two circles at different heights. From the distance of these two points using the two heights and the source to EPID distance, the authors calculate the distance of the beam spot from the CAOR. Measurements with all two techniques were performed on an Elekta Linac. Measurements were performed with the beam spot in nominal clinical position and in a deliberately offset position. Measurements were also performed using the Flexmap image registration/ball-bearing test.
Results:
Within their uncertainties, both methods report the same beam spot displacement. In clinical use, a total of 203 monthly beam spot measurements on 14 different beams showed an average displacement of 0.11 mm (σ = 0.07 mm) in-plane and 0.10 mm (σ = 0.07 mm) cross-plane with maximum displacement of 0.37 mm in-plane and 0.34 mm cross-plane.
Conclusions:
The methods described provide a quantitative measure of beam spot position, are easy t |
| doi_str_mv | 10.1118/1.4766270 |
| format | Article |
| fullrecord | <record><control><sourceid>proquest_pubme</sourceid><recordid>TN_cdi_pubmed_primary_23231311</recordid><sourceformat>XML</sourceformat><sourcesystem>PC</sourcesystem><sourcerecordid>1238108134</sourcerecordid><originalsourceid>FETCH-LOGICAL-c4210-25384dd671498d4eb8e19c18ed2e726ae487443a4066f0405431420852c64f783</originalsourceid><addsrcrecordid>eNp9kE9LwzAYh4MoOv8c_AJS8KJC5_smWZsdZTgVJnrQc-jSt67SNjXJHPv2dnSKFz2FwMOT_B7GThGGiKiucSjTJOEp7LABl6mIJYfxLhsAjGXMJYwO2KH37wCQiBHsswMuuECBOGDTl5WNPFVF7KggR40pm7eoprCwuY8K66KwoO6e-aWjmpoQ2SKaU1ZHvrUhaq0vQ2mbY7ZXZJWnk-15xF6nty-T-3j2dPcwuZnFRnKEmI-EknmepCjHKpc0V4Rjg4pyTilPMpIqlVJkEpKkgO7jUmC3RY24SWSRKnHEznuv9aHU3pSBzMLYpiETNO9WpwAb6qKnWmc_luSDrktvqKqyhuzSa-RCISgUskMve9Q4633XQLeurDO31gh6E1ej3sbt2LOtdjmvKf8hv2t2QNwDq7Ki9d8m_fi8FV71_GZItun47-t_wp_W_ZK3eSG-ACABmpQ</addsrcrecordid><sourcetype>Open Access Repository</sourcetype><iscdi>true</iscdi><recordtype>article</recordtype><pqid>1238108134</pqid></control><display><type>article</type><title>Two self-referencing methods for the measurement of beam spot position</title><source>MEDLINE</source><source>Access via Wiley Online Library</source><source>Alma/SFX Local Collection</source><creator>Nyiri, Balazs J. ; Smale, Jason R. ; Gerig, Lee H.</creator><creatorcontrib>Nyiri, Balazs J. ; Smale, Jason R. ; Gerig, Lee H.</creatorcontrib><description>Purpose:
Two quantitative methods of measuring electron beam spot position with respect to the collimator axis of rotation (CAOR) are described.
Methods:
Method 1 uses a cylindrical ion chamber (IC) mounted on a jig corotational with the collimator making the relationship among the chamber, jaws, and CAOR fixed and independent of collimator angle. A jaw parallel to the IC axis is set to zero and the IC position adjusted so that the IC signal is approximately 50% of the open field value, providing a large dose gradient in the region of the IC. The cGy/MU value is measured as a function of collimator rotation, e.g., every 30°. If the beam spot does not lie on the CAOR, the signal from the ion chamber will vary with collimator rotation. Based on a measured spatial sensitivity, the distance of the beam spot from the CAOR can be calculated from the IC signal variation with rotation. The 2nd method is image based. Two stainless steel rods, 3 mm in diameter, are mounted to a jig attached to the Linac collimator. The rods, offset from the CAOR, lay in different planes normal to the CAOR, one at 158 cm SSD and the other at 70 cm SSD. As the collimator rotates the rods move tangent along an envelope circle, the centers of which are on the CAOR in their respective planes. Three images, each at a different collimator rotation, containing the shadows of both rods, are acquired on the Linac EPID. At each angle the shadow of the rods on the EPID defines lines tangent to the projection of the envelope circles. From these the authors determine the projected centers of the two circles at different heights. From the distance of these two points using the two heights and the source to EPID distance, the authors calculate the distance of the beam spot from the CAOR. Measurements with all two techniques were performed on an Elekta Linac. Measurements were performed with the beam spot in nominal clinical position and in a deliberately offset position. Measurements were also performed using the Flexmap image registration/ball-bearing test.
Results:
Within their uncertainties, both methods report the same beam spot displacement. In clinical use, a total of 203 monthly beam spot measurements on 14 different beams showed an average displacement of 0.11 mm (σ = 0.07 mm) in-plane and 0.10 mm (σ = 0.07 mm) cross-plane with maximum displacement of 0.37 mm in-plane and 0.34 mm cross-plane.
Conclusions:
The methods described provide a quantitative measure of beam spot position, are easy to use, and provide another tool for Linac setup and quality assurance. Fundamental to the techniques is that they are self-referencing–i.e., they do not require the user to independently define the CAOR.</description><identifier>ISSN: 0094-2405</identifier><identifier>EISSN: 2473-4209</identifier><identifier>DOI: 10.1118/1.4766270</identifier><identifier>PMID: 23231311</identifier><identifier>CODEN: MPHYA6</identifier><language>eng</language><publisher>United States: American Association of Physicists in Medicine</publisher><subject>60 APPLIED LIFE SCIENCES ; Algorithms ; beam spot ; biomedical equipment ; Biomedical instrumentation and transducers, including micro‐electro‐mechanical systems (MEMS) ; Cameras ; COLLIMATORS ; corotational ; electron accelerators ; Electron and positron beams ; ELECTRON BEAMS ; Integrated circuits ; IONIZATION CHAMBERS ; JIGS ; Linac focal spot ; LINEAR ACCELERATORS ; Medical imaging ; Models, Theoretical ; Monte Carlo Method ; PARTICLE ACCELERATORS ; particle beam diagnostics ; Photons ; QUALITY ASSURANCE ; Quality assurance in radiotherapy ; RADIATION DOSES ; radiation therapy ; RADIOLOGY AND NUCLEAR MEDICINE ; Radiometry - methods ; RADIOTHERAPY ; Radiotherapy Dosage ; Radiotherapy Planning, Computer-Assisted - methods ; Radiotherapy, Conformal - methods ; ROTATION ; Rotation measurement ; SENSITIVITY ; spatial variables measurement ; STAINLESS STEELS ; Therapeutic applications, including brachytherapy ; X‐ray imaging</subject><ispartof>Medical physics (Lancaster), 2012-12, Vol.39 (12), p.7635-7643</ispartof><rights>American Association of Physicists in Medicine</rights><rights>2012 American Association of Physicists in Medicine</rights><lds50>peer_reviewed</lds50><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c4210-25384dd671498d4eb8e19c18ed2e726ae487443a4066f0405431420852c64f783</citedby><cites>FETCH-LOGICAL-c4210-25384dd671498d4eb8e19c18ed2e726ae487443a4066f0405431420852c64f783</cites></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><linktopdf>$$Uhttps://onlinelibrary.wiley.com/doi/pdf/10.1118%2F1.4766270$$EPDF$$P50$$Gwiley$$H</linktopdf><linktohtml>$$Uhttps://onlinelibrary.wiley.com/doi/full/10.1118%2F1.4766270$$EHTML$$P50$$Gwiley$$H</linktohtml><link.rule.ids>230,314,780,784,885,1417,27924,27925,45574,45575</link.rule.ids><backlink>$$Uhttps://www.ncbi.nlm.nih.gov/pubmed/23231311$$D View this record in MEDLINE/PubMed$$Hfree_for_read</backlink><backlink>$$Uhttps://www.osti.gov/biblio/22097008$$D View this record in Osti.gov$$Hfree_for_read</backlink></links><search><creatorcontrib>Nyiri, Balazs J.</creatorcontrib><creatorcontrib>Smale, Jason R.</creatorcontrib><creatorcontrib>Gerig, Lee H.</creatorcontrib><title>Two self-referencing methods for the measurement of beam spot position</title><title>Medical physics (Lancaster)</title><addtitle>Med Phys</addtitle><description>Purpose:
Two quantitative methods of measuring electron beam spot position with respect to the collimator axis of rotation (CAOR) are described.
Methods:
Method 1 uses a cylindrical ion chamber (IC) mounted on a jig corotational with the collimator making the relationship among the chamber, jaws, and CAOR fixed and independent of collimator angle. A jaw parallel to the IC axis is set to zero and the IC position adjusted so that the IC signal is approximately 50% of the open field value, providing a large dose gradient in the region of the IC. The cGy/MU value is measured as a function of collimator rotation, e.g., every 30°. If the beam spot does not lie on the CAOR, the signal from the ion chamber will vary with collimator rotation. Based on a measured spatial sensitivity, the distance of the beam spot from the CAOR can be calculated from the IC signal variation with rotation. The 2nd method is image based. Two stainless steel rods, 3 mm in diameter, are mounted to a jig attached to the Linac collimator. The rods, offset from the CAOR, lay in different planes normal to the CAOR, one at 158 cm SSD and the other at 70 cm SSD. As the collimator rotates the rods move tangent along an envelope circle, the centers of which are on the CAOR in their respective planes. Three images, each at a different collimator rotation, containing the shadows of both rods, are acquired on the Linac EPID. At each angle the shadow of the rods on the EPID defines lines tangent to the projection of the envelope circles. From these the authors determine the projected centers of the two circles at different heights. From the distance of these two points using the two heights and the source to EPID distance, the authors calculate the distance of the beam spot from the CAOR. Measurements with all two techniques were performed on an Elekta Linac. Measurements were performed with the beam spot in nominal clinical position and in a deliberately offset position. Measurements were also performed using the Flexmap image registration/ball-bearing test.
Results:
Within their uncertainties, both methods report the same beam spot displacement. In clinical use, a total of 203 monthly beam spot measurements on 14 different beams showed an average displacement of 0.11 mm (σ = 0.07 mm) in-plane and 0.10 mm (σ = 0.07 mm) cross-plane with maximum displacement of 0.37 mm in-plane and 0.34 mm cross-plane.
Conclusions:
The methods described provide a quantitative measure of beam spot position, are easy to use, and provide another tool for Linac setup and quality assurance. Fundamental to the techniques is that they are self-referencing–i.e., they do not require the user to independently define the CAOR.</description><subject>60 APPLIED LIFE SCIENCES</subject><subject>Algorithms</subject><subject>beam spot</subject><subject>biomedical equipment</subject><subject>Biomedical instrumentation and transducers, including micro‐electro‐mechanical systems (MEMS)</subject><subject>Cameras</subject><subject>COLLIMATORS</subject><subject>corotational</subject><subject>electron accelerators</subject><subject>Electron and positron beams</subject><subject>ELECTRON BEAMS</subject><subject>Integrated circuits</subject><subject>IONIZATION CHAMBERS</subject><subject>JIGS</subject><subject>Linac focal spot</subject><subject>LINEAR ACCELERATORS</subject><subject>Medical imaging</subject><subject>Models, Theoretical</subject><subject>Monte Carlo Method</subject><subject>PARTICLE ACCELERATORS</subject><subject>particle beam diagnostics</subject><subject>Photons</subject><subject>QUALITY ASSURANCE</subject><subject>Quality assurance in radiotherapy</subject><subject>RADIATION DOSES</subject><subject>radiation therapy</subject><subject>RADIOLOGY AND NUCLEAR MEDICINE</subject><subject>Radiometry - methods</subject><subject>RADIOTHERAPY</subject><subject>Radiotherapy Dosage</subject><subject>Radiotherapy Planning, Computer-Assisted - methods</subject><subject>Radiotherapy, Conformal - methods</subject><subject>ROTATION</subject><subject>Rotation measurement</subject><subject>SENSITIVITY</subject><subject>spatial variables measurement</subject><subject>STAINLESS STEELS</subject><subject>Therapeutic applications, including brachytherapy</subject><subject>X‐ray imaging</subject><issn>0094-2405</issn><issn>2473-4209</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2012</creationdate><recordtype>article</recordtype><sourceid>EIF</sourceid><recordid>eNp9kE9LwzAYh4MoOv8c_AJS8KJC5_smWZsdZTgVJnrQc-jSt67SNjXJHPv2dnSKFz2FwMOT_B7GThGGiKiucSjTJOEp7LABl6mIJYfxLhsAjGXMJYwO2KH37wCQiBHsswMuuECBOGDTl5WNPFVF7KggR40pm7eoprCwuY8K66KwoO6e-aWjmpoQ2SKaU1ZHvrUhaq0vQ2mbY7ZXZJWnk-15xF6nty-T-3j2dPcwuZnFRnKEmI-EknmepCjHKpc0V4Rjg4pyTilPMpIqlVJkEpKkgO7jUmC3RY24SWSRKnHEznuv9aHU3pSBzMLYpiETNO9WpwAb6qKnWmc_luSDrktvqKqyhuzSa-RCISgUskMve9Q4633XQLeurDO31gh6E1ej3sbt2LOtdjmvKf8hv2t2QNwDq7Ki9d8m_fi8FV71_GZItun47-t_wp_W_ZK3eSG-ACABmpQ</recordid><startdate>201212</startdate><enddate>201212</enddate><creator>Nyiri, Balazs J.</creator><creator>Smale, Jason R.</creator><creator>Gerig, Lee H.</creator><general>American Association of Physicists in Medicine</general><scope>CGR</scope><scope>CUY</scope><scope>CVF</scope><scope>ECM</scope><scope>EIF</scope><scope>NPM</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7X8</scope><scope>OTOTI</scope></search><sort><creationdate>201212</creationdate><title>Two self-referencing methods for the measurement of beam spot position</title><author>Nyiri, Balazs J. ; Smale, Jason R. ; Gerig, Lee H.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c4210-25384dd671498d4eb8e19c18ed2e726ae487443a4066f0405431420852c64f783</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2012</creationdate><topic>60 APPLIED LIFE SCIENCES</topic><topic>Algorithms</topic><topic>beam spot</topic><topic>biomedical equipment</topic><topic>Biomedical instrumentation and transducers, including micro‐electro‐mechanical systems (MEMS)</topic><topic>Cameras</topic><topic>COLLIMATORS</topic><topic>corotational</topic><topic>electron accelerators</topic><topic>Electron and positron beams</topic><topic>ELECTRON BEAMS</topic><topic>Integrated circuits</topic><topic>IONIZATION CHAMBERS</topic><topic>JIGS</topic><topic>Linac focal spot</topic><topic>LINEAR ACCELERATORS</topic><topic>Medical imaging</topic><topic>Models, Theoretical</topic><topic>Monte Carlo Method</topic><topic>PARTICLE ACCELERATORS</topic><topic>particle beam diagnostics</topic><topic>Photons</topic><topic>QUALITY ASSURANCE</topic><topic>Quality assurance in radiotherapy</topic><topic>RADIATION DOSES</topic><topic>radiation therapy</topic><topic>RADIOLOGY AND NUCLEAR MEDICINE</topic><topic>Radiometry - methods</topic><topic>RADIOTHERAPY</topic><topic>Radiotherapy Dosage</topic><topic>Radiotherapy Planning, Computer-Assisted - methods</topic><topic>Radiotherapy, Conformal - methods</topic><topic>ROTATION</topic><topic>Rotation measurement</topic><topic>SENSITIVITY</topic><topic>spatial variables measurement</topic><topic>STAINLESS STEELS</topic><topic>Therapeutic applications, including brachytherapy</topic><topic>X‐ray imaging</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Nyiri, Balazs J.</creatorcontrib><creatorcontrib>Smale, Jason R.</creatorcontrib><creatorcontrib>Gerig, Lee H.</creatorcontrib><collection>Medline</collection><collection>MEDLINE</collection><collection>MEDLINE (Ovid)</collection><collection>MEDLINE</collection><collection>MEDLINE</collection><collection>PubMed</collection><collection>CrossRef</collection><collection>MEDLINE - Academic</collection><collection>OSTI.GOV</collection><jtitle>Medical physics (Lancaster)</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Nyiri, Balazs J.</au><au>Smale, Jason R.</au><au>Gerig, Lee H.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Two self-referencing methods for the measurement of beam spot position</atitle><jtitle>Medical physics (Lancaster)</jtitle><addtitle>Med Phys</addtitle><date>2012-12</date><risdate>2012</risdate><volume>39</volume><issue>12</issue><spage>7635</spage><epage>7643</epage><pages>7635-7643</pages><issn>0094-2405</issn><eissn>2473-4209</eissn><coden>MPHYA6</coden><abstract>Purpose:
Two quantitative methods of measuring electron beam spot position with respect to the collimator axis of rotation (CAOR) are described.
Methods:
Method 1 uses a cylindrical ion chamber (IC) mounted on a jig corotational with the collimator making the relationship among the chamber, jaws, and CAOR fixed and independent of collimator angle. A jaw parallel to the IC axis is set to zero and the IC position adjusted so that the IC signal is approximately 50% of the open field value, providing a large dose gradient in the region of the IC. The cGy/MU value is measured as a function of collimator rotation, e.g., every 30°. If the beam spot does not lie on the CAOR, the signal from the ion chamber will vary with collimator rotation. Based on a measured spatial sensitivity, the distance of the beam spot from the CAOR can be calculated from the IC signal variation with rotation. The 2nd method is image based. Two stainless steel rods, 3 mm in diameter, are mounted to a jig attached to the Linac collimator. The rods, offset from the CAOR, lay in different planes normal to the CAOR, one at 158 cm SSD and the other at 70 cm SSD. As the collimator rotates the rods move tangent along an envelope circle, the centers of which are on the CAOR in their respective planes. Three images, each at a different collimator rotation, containing the shadows of both rods, are acquired on the Linac EPID. At each angle the shadow of the rods on the EPID defines lines tangent to the projection of the envelope circles. From these the authors determine the projected centers of the two circles at different heights. From the distance of these two points using the two heights and the source to EPID distance, the authors calculate the distance of the beam spot from the CAOR. Measurements with all two techniques were performed on an Elekta Linac. Measurements were performed with the beam spot in nominal clinical position and in a deliberately offset position. Measurements were also performed using the Flexmap image registration/ball-bearing test.
Results:
Within their uncertainties, both methods report the same beam spot displacement. In clinical use, a total of 203 monthly beam spot measurements on 14 different beams showed an average displacement of 0.11 mm (σ = 0.07 mm) in-plane and 0.10 mm (σ = 0.07 mm) cross-plane with maximum displacement of 0.37 mm in-plane and 0.34 mm cross-plane.
Conclusions:
The methods described provide a quantitative measure of beam spot position, are easy to use, and provide another tool for Linac setup and quality assurance. Fundamental to the techniques is that they are self-referencing–i.e., they do not require the user to independently define the CAOR.</abstract><cop>United States</cop><pub>American Association of Physicists in Medicine</pub><pmid>23231311</pmid><doi>10.1118/1.4766270</doi><tpages>9</tpages></addata></record> |
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| ispartof | Medical physics (Lancaster), 2012-12, Vol.39 (12), p.7635-7643 |
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| subjects | 60 APPLIED LIFE SCIENCES Algorithms beam spot biomedical equipment Biomedical instrumentation and transducers, including micro‐electro‐mechanical systems (MEMS) Cameras COLLIMATORS corotational electron accelerators Electron and positron beams ELECTRON BEAMS Integrated circuits IONIZATION CHAMBERS JIGS Linac focal spot LINEAR ACCELERATORS Medical imaging Models, Theoretical Monte Carlo Method PARTICLE ACCELERATORS particle beam diagnostics Photons QUALITY ASSURANCE Quality assurance in radiotherapy RADIATION DOSES radiation therapy RADIOLOGY AND NUCLEAR MEDICINE Radiometry - methods RADIOTHERAPY Radiotherapy Dosage Radiotherapy Planning, Computer-Assisted - methods Radiotherapy, Conformal - methods ROTATION Rotation measurement SENSITIVITY spatial variables measurement STAINLESS STEELS Therapeutic applications, including brachytherapy X‐ray imaging |
| title | Two self-referencing methods for the measurement of beam spot position |
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