Measuring linac photon beam energy through EPID image analysis of physically wedged fields
Purpose: Electronic portal imaging devices (EPIDs) have proven to be useful tools for measuring several parameters of interest in linac quality assurance (QA). However, a method for measuring linac photon beam energy using EPIDs has not previously been reported. In this report, such a method is devi...
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| creator | Dawoud, S. M. Weston, S. J. Bond, I. Ward, G. C. Rixham, P. A. Mason, J. Huckle, A. Sykes, J. R. |
| description | Purpose:
Electronic portal imaging devices (EPIDs) have proven to be useful tools for measuring several parameters of interest in linac quality assurance (QA). However, a method for measuring linac photon beam energy using EPIDs has not previously been reported. In this report, such a method is devised and tested, based on fitting a second order polynomial to the profiles of physically wedged beams, where the metric of interest is the second order coefficientα. The relationship between α and the beam quality index [percentage depth dose at 10 cm depth (PDD10)] is examined to produce a suitable calibration curve between these two parameters.
Methods:
Measurements were taken in a water-tank for beams with a range of energies representative of the local QA tolerances about the nominal value 6 MV. In each case, the beam quality was found in terms of PDD10 for 100 × 100 mm2 square fields. EPID images of 200 × 200 mm2 wedged fields were then taken for each beam and the wedge profile was fitted in MATLAB 2010b (The MathWorks, Inc., Natick, MA). α was then plotted against PDD10 and fitted with a linear relation to produce the calibration curve. The uncertainty in α was evaluated by taking five repeat EPID images of the wedged field for a beam of 6 MV nominal energy. The consistency of measuring α was found by taking repeat measurements on a single linac over a three month period. The method was also tested at 10 MV by repeating the water-tank crosscalibration for a range of energies centered approximately about a 10 MV nominal value. Finally, the calibration curve from the test linac and that from a separate clinical machine were compared to test consistency of the method across machines in a matched fleet.
Results:
The relationship betweenα and PDD10 was found to be strongly linear (R2 = 0.979) while the uncertainty in α was found to be negligible compared to that associated with measuring PDD10 in the water-tank (±0.3%). The repeat measurements over a three month period showed the method to be reasonably consistent (i.e., well within the limits defined by local QA tolerances). The measurements were repeated on a matched machine and the same linear relationship between α and PDD10 was observed. The results for both machines were found to be indistinguishable across the energy range of interest (i.e., across and close to the thresholds defined by local QA tolerances), hence a single relation could be established across a matched fleet. Finally, the experiment was |
| doi_str_mv | 10.1118/1.4856075 |
| format | Article |
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Electronic portal imaging devices (EPIDs) have proven to be useful tools for measuring several parameters of interest in linac quality assurance (QA). However, a method for measuring linac photon beam energy using EPIDs has not previously been reported. In this report, such a method is devised and tested, based on fitting a second order polynomial to the profiles of physically wedged beams, where the metric of interest is the second order coefficientα. The relationship between α and the beam quality index [percentage depth dose at 10 cm depth (PDD10)] is examined to produce a suitable calibration curve between these two parameters.
Methods:
Measurements were taken in a water-tank for beams with a range of energies representative of the local QA tolerances about the nominal value 6 MV. In each case, the beam quality was found in terms of PDD10 for 100 × 100 mm2 square fields. EPID images of 200 × 200 mm2 wedged fields were then taken for each beam and the wedge profile was fitted in MATLAB 2010b (The MathWorks, Inc., Natick, MA). α was then plotted against PDD10 and fitted with a linear relation to produce the calibration curve. The uncertainty in α was evaluated by taking five repeat EPID images of the wedged field for a beam of 6 MV nominal energy. The consistency of measuring α was found by taking repeat measurements on a single linac over a three month period. The method was also tested at 10 MV by repeating the water-tank crosscalibration for a range of energies centered approximately about a 10 MV nominal value. Finally, the calibration curve from the test linac and that from a separate clinical machine were compared to test consistency of the method across machines in a matched fleet.
Results:
The relationship betweenα and PDD10 was found to be strongly linear (R2 = 0.979) while the uncertainty in α was found to be negligible compared to that associated with measuring PDD10 in the water-tank (±0.3%). The repeat measurements over a three month period showed the method to be reasonably consistent (i.e., well within the limits defined by local QA tolerances). The measurements were repeated on a matched machine and the same linear relationship between α and PDD10 was observed. The results for both machines were found to be indistinguishable across the energy range of interest (i.e., across and close to the thresholds defined by local QA tolerances), hence a single relation could be established across a matched fleet. Finally, the experiment was repeated on both linacs at 10 MV, where the linear relationship between α and PDD10 was again observed.
Conclusions:
The authors conclude that EPID image analysis of physically wedged beam profiles can be used to measure linac photon beam energy. The uncertainty in such a measurement is dominated by that associated with measuring PDD10 in the water-tank; hence, the accuracies of these two methods are directly comparable. This method provides a useful technique for quickly performing energy constancy measurements while saving significant clinical downtime for QA.</description><identifier>ISSN: 0094-2405</identifier><identifier>EISSN: 2473-4209</identifier><identifier>DOI: 10.1118/1.4856075</identifier><identifier>PMID: 24506599</identifier><identifier>CODEN: MPHYA6</identifier><language>eng</language><publisher>United States: American Association of Physicists in Medicine</publisher><subject>ACCURACY ; BEAM PROFILES ; Biological material, e.g. blood, urine; Haemocytometers ; Calibrating of instruments or apparatus ; CALIBRATION ; Collimators ; DEPTH DOSE DISTRIBUTIONS ; Digital computing or data processing equipment or methods, specially adapted for specific applications ; Electrical Equipment and Supplies ; energy ; ENERGY RANGE ; EPID ; Error analysis ; image analysis ; Image data processing or generation, in general ; Image guided radiation therapy ; IMAGE PROCESSING ; LINEAR ACCELERATORS ; Medical image artifacts ; medical image processing ; Medical imaging ; METRICS ; Particle Accelerators - instrumentation ; PHOTON BEAMS ; Photons ; Photons - therapeutic use ; POLYNOMIALS ; QUALITY ASSURANCE ; Quality Control ; RADIATION PROTECTION AND DOSIMETRY ; radiation therapy ; Radiation therapy equipment ; radiotherapy ; Standards and calibration ; Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00 ; TOLERANCE ; Treatment strategy ; wedge</subject><ispartof>Medical physics (Lancaster), 2014-02, Vol.41 (2), p.021708-n/a</ispartof><rights>American Association of Physicists in Medicine</rights><rights>2014 American Association of Physicists in Medicine</rights><lds50>peer_reviewed</lds50><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c4215-5c69bcf725f28ba0077f1b2d24d290bffcb2ae5715a8f497530904005f9c836e3</citedby><cites>FETCH-LOGICAL-c4215-5c69bcf725f28ba0077f1b2d24d290bffcb2ae5715a8f497530904005f9c836e3</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%2F1.4856075$$EPDF$$P50$$Gwiley$$H</linktopdf><linktohtml>$$Uhttps://onlinelibrary.wiley.com/doi/full/10.1118%2F1.4856075$$EHTML$$P50$$Gwiley$$H</linktohtml><link.rule.ids>230,314,777,781,882,1412,27905,27906,45555,45556</link.rule.ids><backlink>$$Uhttps://www.ncbi.nlm.nih.gov/pubmed/24506599$$D View this record in MEDLINE/PubMed$$Hfree_for_read</backlink><backlink>$$Uhttps://www.osti.gov/biblio/22251695$$D View this record in Osti.gov$$Hfree_for_read</backlink></links><search><creatorcontrib>Dawoud, S. M.</creatorcontrib><creatorcontrib>Weston, S. J.</creatorcontrib><creatorcontrib>Bond, I.</creatorcontrib><creatorcontrib>Ward, G. C.</creatorcontrib><creatorcontrib>Rixham, P. A.</creatorcontrib><creatorcontrib>Mason, J.</creatorcontrib><creatorcontrib>Huckle, A.</creatorcontrib><creatorcontrib>Sykes, J. R.</creatorcontrib><title>Measuring linac photon beam energy through EPID image analysis of physically wedged fields</title><title>Medical physics (Lancaster)</title><addtitle>Med Phys</addtitle><description>Purpose:
Electronic portal imaging devices (EPIDs) have proven to be useful tools for measuring several parameters of interest in linac quality assurance (QA). However, a method for measuring linac photon beam energy using EPIDs has not previously been reported. In this report, such a method is devised and tested, based on fitting a second order polynomial to the profiles of physically wedged beams, where the metric of interest is the second order coefficientα. The relationship between α and the beam quality index [percentage depth dose at 10 cm depth (PDD10)] is examined to produce a suitable calibration curve between these two parameters.
Methods:
Measurements were taken in a water-tank for beams with a range of energies representative of the local QA tolerances about the nominal value 6 MV. In each case, the beam quality was found in terms of PDD10 for 100 × 100 mm2 square fields. EPID images of 200 × 200 mm2 wedged fields were then taken for each beam and the wedge profile was fitted in MATLAB 2010b (The MathWorks, Inc., Natick, MA). α was then plotted against PDD10 and fitted with a linear relation to produce the calibration curve. The uncertainty in α was evaluated by taking five repeat EPID images of the wedged field for a beam of 6 MV nominal energy. The consistency of measuring α was found by taking repeat measurements on a single linac over a three month period. The method was also tested at 10 MV by repeating the water-tank crosscalibration for a range of energies centered approximately about a 10 MV nominal value. Finally, the calibration curve from the test linac and that from a separate clinical machine were compared to test consistency of the method across machines in a matched fleet.
Results:
The relationship betweenα and PDD10 was found to be strongly linear (R2 = 0.979) while the uncertainty in α was found to be negligible compared to that associated with measuring PDD10 in the water-tank (±0.3%). The repeat measurements over a three month period showed the method to be reasonably consistent (i.e., well within the limits defined by local QA tolerances). The measurements were repeated on a matched machine and the same linear relationship between α and PDD10 was observed. The results for both machines were found to be indistinguishable across the energy range of interest (i.e., across and close to the thresholds defined by local QA tolerances), hence a single relation could be established across a matched fleet. Finally, the experiment was repeated on both linacs at 10 MV, where the linear relationship between α and PDD10 was again observed.
Conclusions:
The authors conclude that EPID image analysis of physically wedged beam profiles can be used to measure linac photon beam energy. The uncertainty in such a measurement is dominated by that associated with measuring PDD10 in the water-tank; hence, the accuracies of these two methods are directly comparable. This method provides a useful technique for quickly performing energy constancy measurements while saving significant clinical downtime for QA.</description><subject>ACCURACY</subject><subject>BEAM PROFILES</subject><subject>Biological material, e.g. blood, urine; Haemocytometers</subject><subject>Calibrating of instruments or apparatus</subject><subject>CALIBRATION</subject><subject>Collimators</subject><subject>DEPTH DOSE DISTRIBUTIONS</subject><subject>Digital computing or data processing equipment or methods, specially adapted for specific applications</subject><subject>Electrical Equipment and Supplies</subject><subject>energy</subject><subject>ENERGY RANGE</subject><subject>EPID</subject><subject>Error analysis</subject><subject>image analysis</subject><subject>Image data processing or generation, in general</subject><subject>Image guided radiation therapy</subject><subject>IMAGE PROCESSING</subject><subject>LINEAR ACCELERATORS</subject><subject>Medical image artifacts</subject><subject>medical image processing</subject><subject>Medical imaging</subject><subject>METRICS</subject><subject>Particle Accelerators - instrumentation</subject><subject>PHOTON BEAMS</subject><subject>Photons</subject><subject>Photons - therapeutic use</subject><subject>POLYNOMIALS</subject><subject>QUALITY ASSURANCE</subject><subject>Quality Control</subject><subject>RADIATION PROTECTION AND DOSIMETRY</subject><subject>radiation therapy</subject><subject>Radiation therapy equipment</subject><subject>radiotherapy</subject><subject>Standards and calibration</subject><subject>Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00</subject><subject>TOLERANCE</subject><subject>Treatment strategy</subject><subject>wedge</subject><issn>0094-2405</issn><issn>2473-4209</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2014</creationdate><recordtype>article</recordtype><sourceid>EIF</sourceid><recordid>eNp90E1v1DAQBmALUdGlcOAPIEtcACll_JXEx6oUWqkVPcCFi-U446xRNl7shCr_nlRZUC_taXx4_I7mJeQNg1PGWP2JncpalVCpZ2TDZSUKyUE_JxsALQsuQR2Tlzn_AoBSKHhBjrlUUCqtN-TnDdo8pTB0tA-DdXS_jWMcaIN2R3HA1M103KY4dVt6cXv1mYad7ZDawfZzDplGv_xYXs72_UzvsO2wpT5g3-ZX5MjbPuPrwzwhP75cfD-_LK6_fb06P7sunORMFcqVunG-4srzurEAVeVZw1suW66h8d413KKqmLK1l7pSAjRIAOW1q0WJ4oS8W3NjHoPJLozoti4OA7rRcM4VK7Va1PtV7VP8PWEezS5kh31vB4xTNkxqzUQlhVjoh5W6FHNO6M0-LWen2TAw94UbZg6FL_btIXZqdtj-l_8aXkCxgrvQ4_x4krm5PQR-XP39IXYMcXhy-6P4T0wPwvetF38BUBqjMw</recordid><startdate>201402</startdate><enddate>201402</enddate><creator>Dawoud, S. M.</creator><creator>Weston, S. J.</creator><creator>Bond, I.</creator><creator>Ward, G. C.</creator><creator>Rixham, P. A.</creator><creator>Mason, J.</creator><creator>Huckle, A.</creator><creator>Sykes, J. R.</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>201402</creationdate><title>Measuring linac photon beam energy through EPID image analysis of physically wedged fields</title><author>Dawoud, S. M. ; Weston, S. J. ; Bond, I. ; Ward, G. C. ; Rixham, P. A. ; Mason, J. ; Huckle, A. ; Sykes, J. R.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c4215-5c69bcf725f28ba0077f1b2d24d290bffcb2ae5715a8f497530904005f9c836e3</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2014</creationdate><topic>ACCURACY</topic><topic>BEAM PROFILES</topic><topic>Biological material, e.g. blood, urine; Haemocytometers</topic><topic>Calibrating of instruments or apparatus</topic><topic>CALIBRATION</topic><topic>Collimators</topic><topic>DEPTH DOSE DISTRIBUTIONS</topic><topic>Digital computing or data processing equipment or methods, specially adapted for specific applications</topic><topic>Electrical Equipment and Supplies</topic><topic>energy</topic><topic>ENERGY RANGE</topic><topic>EPID</topic><topic>Error analysis</topic><topic>image analysis</topic><topic>Image data processing or generation, in general</topic><topic>Image guided radiation therapy</topic><topic>IMAGE PROCESSING</topic><topic>LINEAR ACCELERATORS</topic><topic>Medical image artifacts</topic><topic>medical image processing</topic><topic>Medical imaging</topic><topic>METRICS</topic><topic>Particle Accelerators - instrumentation</topic><topic>PHOTON BEAMS</topic><topic>Photons</topic><topic>Photons - therapeutic use</topic><topic>POLYNOMIALS</topic><topic>QUALITY ASSURANCE</topic><topic>Quality Control</topic><topic>RADIATION PROTECTION AND DOSIMETRY</topic><topic>radiation therapy</topic><topic>Radiation therapy equipment</topic><topic>radiotherapy</topic><topic>Standards and calibration</topic><topic>Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00</topic><topic>TOLERANCE</topic><topic>Treatment strategy</topic><topic>wedge</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Dawoud, S. M.</creatorcontrib><creatorcontrib>Weston, S. J.</creatorcontrib><creatorcontrib>Bond, I.</creatorcontrib><creatorcontrib>Ward, G. C.</creatorcontrib><creatorcontrib>Rixham, P. A.</creatorcontrib><creatorcontrib>Mason, J.</creatorcontrib><creatorcontrib>Huckle, A.</creatorcontrib><creatorcontrib>Sykes, J. R.</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>Dawoud, S. M.</au><au>Weston, S. J.</au><au>Bond, I.</au><au>Ward, G. C.</au><au>Rixham, P. A.</au><au>Mason, J.</au><au>Huckle, A.</au><au>Sykes, J. R.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Measuring linac photon beam energy through EPID image analysis of physically wedged fields</atitle><jtitle>Medical physics (Lancaster)</jtitle><addtitle>Med Phys</addtitle><date>2014-02</date><risdate>2014</risdate><volume>41</volume><issue>2</issue><spage>021708</spage><epage>n/a</epage><pages>021708-n/a</pages><issn>0094-2405</issn><eissn>2473-4209</eissn><coden>MPHYA6</coden><abstract>Purpose:
Electronic portal imaging devices (EPIDs) have proven to be useful tools for measuring several parameters of interest in linac quality assurance (QA). However, a method for measuring linac photon beam energy using EPIDs has not previously been reported. In this report, such a method is devised and tested, based on fitting a second order polynomial to the profiles of physically wedged beams, where the metric of interest is the second order coefficientα. The relationship between α and the beam quality index [percentage depth dose at 10 cm depth (PDD10)] is examined to produce a suitable calibration curve between these two parameters.
Methods:
Measurements were taken in a water-tank for beams with a range of energies representative of the local QA tolerances about the nominal value 6 MV. In each case, the beam quality was found in terms of PDD10 for 100 × 100 mm2 square fields. EPID images of 200 × 200 mm2 wedged fields were then taken for each beam and the wedge profile was fitted in MATLAB 2010b (The MathWorks, Inc., Natick, MA). α was then plotted against PDD10 and fitted with a linear relation to produce the calibration curve. The uncertainty in α was evaluated by taking five repeat EPID images of the wedged field for a beam of 6 MV nominal energy. The consistency of measuring α was found by taking repeat measurements on a single linac over a three month period. The method was also tested at 10 MV by repeating the water-tank crosscalibration for a range of energies centered approximately about a 10 MV nominal value. Finally, the calibration curve from the test linac and that from a separate clinical machine were compared to test consistency of the method across machines in a matched fleet.
Results:
The relationship betweenα and PDD10 was found to be strongly linear (R2 = 0.979) while the uncertainty in α was found to be negligible compared to that associated with measuring PDD10 in the water-tank (±0.3%). The repeat measurements over a three month period showed the method to be reasonably consistent (i.e., well within the limits defined by local QA tolerances). The measurements were repeated on a matched machine and the same linear relationship between α and PDD10 was observed. The results for both machines were found to be indistinguishable across the energy range of interest (i.e., across and close to the thresholds defined by local QA tolerances), hence a single relation could be established across a matched fleet. Finally, the experiment was repeated on both linacs at 10 MV, where the linear relationship between α and PDD10 was again observed.
Conclusions:
The authors conclude that EPID image analysis of physically wedged beam profiles can be used to measure linac photon beam energy. The uncertainty in such a measurement is dominated by that associated with measuring PDD10 in the water-tank; hence, the accuracies of these two methods are directly comparable. This method provides a useful technique for quickly performing energy constancy measurements while saving significant clinical downtime for QA.</abstract><cop>United States</cop><pub>American Association of Physicists in Medicine</pub><pmid>24506599</pmid><doi>10.1118/1.4856075</doi><tpages>7</tpages></addata></record> |
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| ispartof | Medical physics (Lancaster), 2014-02, Vol.41 (2), p.021708-n/a |
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| source | MEDLINE; Wiley Online Library Journals Frontfile Complete; Alma/SFX Local Collection |
| subjects | ACCURACY BEAM PROFILES Biological material, e.g. blood, urine Haemocytometers Calibrating of instruments or apparatus CALIBRATION Collimators DEPTH DOSE DISTRIBUTIONS Digital computing or data processing equipment or methods, specially adapted for specific applications Electrical Equipment and Supplies energy ENERGY RANGE EPID Error analysis image analysis Image data processing or generation, in general Image guided radiation therapy IMAGE PROCESSING LINEAR ACCELERATORS Medical image artifacts medical image processing Medical imaging METRICS Particle Accelerators - instrumentation PHOTON BEAMS Photons Photons - therapeutic use POLYNOMIALS QUALITY ASSURANCE Quality Control RADIATION PROTECTION AND DOSIMETRY radiation therapy Radiation therapy equipment radiotherapy Standards and calibration Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00 TOLERANCE Treatment strategy wedge |
| title | Measuring linac photon beam energy through EPID image analysis of physically wedged fields |
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