{"title":"Measurement of CT radiation beam width with a pencil ionization chamber and radiopaque mask.","authors":"Rani Al-Senan, David M Gauntt, Gary T Barnes","doi":"10.1002/acm2.70027","DOIUrl":null,"url":null,"abstract":"<p><strong>Purpose: </strong>This study compares fan beam CT scanner radiation beam widths measured with a pencil ionization chamber-radiopaque mask technique with commonly used film and computed radiography (CR) measurements.</p><p><strong>Methods: </strong>For a given fan beam CT scanner x-ray beam, the ionization chamber-mask technique determines the radiation beam width by exposing a 100 mm pencil chamber with and without a radiopaque cylindrical mask of known width that is a fraction of the nominal beam width. Additional widths can then be measured using the same kV, mAs, and pre-patient filtration without the mask. CT scanner radiation beam width measurements with the technique were compared with film and CR techniques.</p><p><strong>Results: </strong>Measurements from 20 different detector configurations/focal spot combinations on fan beam CT scanners from two manufacturers are presented. The root mean square (RMS) difference between the ionization chamber-mask measured beam widths and film measurements was 0.31 mm, with a similar RMS difference of 0.28 mm with CR measurements. These results compare favorably with the RMS difference between film and CR measurements, which was 0.35 mm.</p><p><strong>Conclusion: </strong>This study demonstrates that radiation beam widths of fan beam CT scanners can be measured using the ionization chamber-radiopaque mask method with an RMS accuracy of better than 0.5 mm. We demonstrate the method is applicable to nominal beam widths ranging from 1 to 40 mm.</p>","PeriodicalId":14989,"journal":{"name":"Journal of Applied Clinical Medical Physics","volume":" ","pages":"e70027"},"PeriodicalIF":2.0000,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Applied Clinical Medical Physics","FirstCategoryId":"3","ListUrlMain":"https://doi.org/10.1002/acm2.70027","RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING","Score":null,"Total":0}
Measurement of CT radiation beam width with a pencil ionization chamber and radiopaque mask.
Purpose: This study compares fan beam CT scanner radiation beam widths measured with a pencil ionization chamber-radiopaque mask technique with commonly used film and computed radiography (CR) measurements.
Methods: For a given fan beam CT scanner x-ray beam, the ionization chamber-mask technique determines the radiation beam width by exposing a 100 mm pencil chamber with and without a radiopaque cylindrical mask of known width that is a fraction of the nominal beam width. Additional widths can then be measured using the same kV, mAs, and pre-patient filtration without the mask. CT scanner radiation beam width measurements with the technique were compared with film and CR techniques.
Results: Measurements from 20 different detector configurations/focal spot combinations on fan beam CT scanners from two manufacturers are presented. The root mean square (RMS) difference between the ionization chamber-mask measured beam widths and film measurements was 0.31 mm, with a similar RMS difference of 0.28 mm with CR measurements. These results compare favorably with the RMS difference between film and CR measurements, which was 0.35 mm.
Conclusion: This study demonstrates that radiation beam widths of fan beam CT scanners can be measured using the ionization chamber-radiopaque mask method with an RMS accuracy of better than 0.5 mm. We demonstrate the method is applicable to nominal beam widths ranging from 1 to 40 mm.
期刊介绍：
Journal of Applied Clinical Medical Physics is an international Open Access publication dedicated to clinical medical physics. JACMP welcomes original contributions dealing with all aspects of medical physics from scientists working in the clinical medical physics around the world. JACMP accepts only online submission.
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