CTDI versus New AAPM Metrics to assess Doses in CT: a case study
In modern CT, CTDI100 measurements would underestimate accumulated dose at the gantry center. AAPM TG 111 report proposed improved metrics for CT dosimetry, mainly for helical and wide beam width scanning. In this study, a methodology to assess CT dose, inspired on TG 111, was applied. Dosimeters we...
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Brazilian Radiation Protection Society (Sociedade Brasileira de Proteção Radiológica, SBPR)
2016-11-01
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| Series: | Brazilian Journal of Radiation Sciences |
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| Online Access: | https://bjrs.org.br/revista/index.php/REVISTA/article/view/194 |
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| author | Maria Carolina Santana Campelo Marcia Carvalho Silva Ricardo Andrade Terini |
| author_facet | Maria Carolina Santana Campelo Marcia Carvalho Silva Ricardo Andrade Terini |
| author_sort | Maria Carolina Santana Campelo |
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| description | In modern CT, CTDI100 measurements would underestimate accumulated dose at the gantry center. AAPM TG 111 report proposed improved metrics for CT dosimetry, mainly for helical and wide beam width scanning. In this study, a methodology to assess CT dose, inspired on TG 111, was applied. Dosimeters were firstly calibrated in lab in beams like those utilized clinically. Using a reference 0.6cc Farmer chamber, two CT “pencil” chambers were calibrated in PKL by substitution method. Results showed differences ≤ 2% in the calibration coefficients, for three collimation apertures. A small 0.6cc chamber was calibrated in air kerma with this setup, without any collimator. After this, in a private Brazilian hospital, the small chamber was applied in dosimetry tests of a CT scanner, according to TG 111, determining Dose profiles and Equilibrium dose free-in-air (Deq,air) for some protocols and pitch values. Results showed that Deq,air increased when reducing pitch and Equilibrium dose-pitch product free-in-air (p.Deq,air) remain constant. In measurements with a 450mm CT phantom, differences between Planar Average Equilibrium Dose (Deq,p) and CTDIvol ranged between 30-37%. This occurs because CTDIvol cannot include dose profile "tail" contribution, caused by scattering in phantom, especially for wide beam widths. |
| format | Article |
| id | doaj-art-e54b05ffdf31450aac1ade38d5c212f0 |
| institution | DOAJ |
| issn | 2319-0612 |
| language | English |
| publishDate | 2016-11-01 |
| publisher | Brazilian Radiation Protection Society (Sociedade Brasileira de Proteção Radiológica, SBPR) |
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| series | Brazilian Journal of Radiation Sciences |
| spelling | doaj-art-e54b05ffdf31450aac1ade38d5c212f02025-08-20T02:39:41ZengBrazilian Radiation Protection Society (Sociedade Brasileira de Proteção Radiológica, SBPR)Brazilian Journal of Radiation Sciences2319-06122016-11-014210.15392/bjrs.v4i2.194155CTDI versus New AAPM Metrics to assess Doses in CT: a case studyMaria Carolina Santana Campelo0Marcia Carvalho Silva1Ricardo Andrade Terini2Bacharel em Física, Pontifícia Universidade Católica de São Paulo, SPFísica Médica, Hospital Israelita Albert Einstein (HIAE), SPLaboratório de Ensaios Não-Destrutivos - Instituto de Energia e Meio Ambiente - Universidade de São Paulo, SPIn modern CT, CTDI100 measurements would underestimate accumulated dose at the gantry center. AAPM TG 111 report proposed improved metrics for CT dosimetry, mainly for helical and wide beam width scanning. In this study, a methodology to assess CT dose, inspired on TG 111, was applied. Dosimeters were firstly calibrated in lab in beams like those utilized clinically. Using a reference 0.6cc Farmer chamber, two CT “pencil” chambers were calibrated in PKL by substitution method. Results showed differences ≤ 2% in the calibration coefficients, for three collimation apertures. A small 0.6cc chamber was calibrated in air kerma with this setup, without any collimator. After this, in a private Brazilian hospital, the small chamber was applied in dosimetry tests of a CT scanner, according to TG 111, determining Dose profiles and Equilibrium dose free-in-air (Deq,air) for some protocols and pitch values. Results showed that Deq,air increased when reducing pitch and Equilibrium dose-pitch product free-in-air (p.Deq,air) remain constant. In measurements with a 450mm CT phantom, differences between Planar Average Equilibrium Dose (Deq,p) and CTDIvol ranged between 30-37%. This occurs because CTDIvol cannot include dose profile "tail" contribution, caused by scattering in phantom, especially for wide beam widths.https://bjrs.org.br/revista/index.php/REVISTA/article/view/194computed tomographyaapm tg 111ctdi |
| spellingShingle | Maria Carolina Santana Campelo Marcia Carvalho Silva Ricardo Andrade Terini CTDI versus New AAPM Metrics to assess Doses in CT: a case study Brazilian Journal of Radiation Sciences computed tomography aapm tg 111 ctdi |
| title | CTDI versus New AAPM Metrics to assess Doses in CT: a case study |
| title_full | CTDI versus New AAPM Metrics to assess Doses in CT: a case study |
| title_fullStr | CTDI versus New AAPM Metrics to assess Doses in CT: a case study |
| title_full_unstemmed | CTDI versus New AAPM Metrics to assess Doses in CT: a case study |
| title_short | CTDI versus New AAPM Metrics to assess Doses in CT: a case study |
| title_sort | ctdi versus new aapm metrics to assess doses in ct a case study |
| topic | computed tomography aapm tg 111 ctdi |
| url | https://bjrs.org.br/revista/index.php/REVISTA/article/view/194 |
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