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Consistency of Faraday cup and ionization chamber dosimetry of proton fields and the role of nuclear interactions.

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Title: Consistency of Faraday cup and ionization chamber dosimetry of proton fields and the role of nuclear interactions.
Authors: Wulff, Jörg1,2,3 (AUTHOR), Paul, Anne1,2,3,4 (AUTHOR), Bäcker, Claus Maximilian1,2,3 (AUTHOR), Baumann, Kilian‐Simon5,6,7 (AUTHOR), Esser, Johannes Niklas1,2,3 (AUTHOR), Koska, Benjamin1,2,3 (AUTHOR), Timmermann, Beate1,2,3,4,8,9 (AUTHOR), Verbeek, Nico Gerd1,2,3 (AUTHOR), Bäumer, Christian1,2,3,8,10 (AUTHOR) christian.baeumer@uk-essen.de
Source: Medical Physics. Mar2024, Vol. 51 Issue 3, p2277-2292. 16p.
Subjects: Ionization chambers, Photon beams, Radiation dosimetry, Reciprocity theorems, Absorbed dose, Protons, Proton therapy
Abstract: Background: A Faraday cup (FC) facilitates a quite clean measurement of the proton fluence emerging from clinical spot‐scanning nozzles with narrow pencil‐beams. The utilization of FCs appears to be an attractive option for high dose rate delivery modes and the source models of Monte‐Carlo (MC) dose engines. However, previous studies revealed discrepancies of 3%–6% between reference dosimetry with ionization chambers (ICs) and FC‐based dosimetry. This has prevented the widespread use of FCs for dosimetry in proton therapy. Purpose: The current study aims at bridging the gap between FC dosimetry and IC dosimetry of proton fields delivered with spot‐scanning treatment heads. Particularly, a novel method to evaluate FC measurements is introduced. Methods: A consistency check is formulated, which makes use of the energy balance and the reciprocity theorem. The measurement data comprise central‐axis depth distributions of the absorbed dose of quasi‐monochromatic fields with a width of about 28.5 cm and FC measurements of the reciprocal fields with a single spot. These data are complemented by a look‐up of energy‐range tables, the average Q‐value of transmutations, and the escape energy carried away by neutrons and photons. The latter data are computed by MC simulations, which in turn are validated with measurements of the distal dose tail and neutron out‐of‐field doses. For comparison, the conventional approach of FC evaluation is performed, which computes absorbed dose from the product of fluence and stopping power. The results from the FC measurements are compared with the standard dosimetry protocols and improved reference dosimetry methods. Results: The deviation between the conventional FC‐based dosimetry and the IC‐based one according to standard dosimetry protocols was −4.7 (±$\pm$ 3.3)% for a 100 MeV field and −3.6 (±$\pm$3.5)% for 200 MeV, thereby agreeing within the reported uncertainties. The deviations could be reduced to −4.0 (±$\pm$ 2.9)% and −3.0 (±$\pm$ 3.1)% by adopting state‐of‐the‐art reference dosimetry methods. The alternative approach using the energy balance gave deviations of only −1.9% (100 MeV) and −2.6% (200 MeV) using state‐of‐the‐art dosimetry. The standard uncertainty of this novel approach was estimated to be about 2%. Conclusions: An alternative concept has been established to determine the absorbed dose of monoenergetic proton fields with an FC. It eliminates the strong dependence of the conventional FC‐based approach on the MC simulation of the stopping‐power and of the secondary ions, which according to the study at hand is the major contributor to the underestimation of the absorbed dose. Some contributions to the uncertainty of the novel approach could potentially be reduced in future studies. This would allow for accurate consistency tests of conventional dosimetry procedures. [ABSTRACT FROM AUTHOR]
Copyright of Medical Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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Items – Name: Title
  Label: Title
  Group: Ti
  Data: Consistency of Faraday cup and ionization chamber dosimetry of proton fields and the role of nuclear interactions.
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  Data: <searchLink fieldCode="AR" term="%22Wulff%2C+Jörg%22">Wulff, Jörg</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Paul%2C+Anne%22">Paul, Anne</searchLink><relatesTo>1,2,3,4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Bäcker%2C+Claus+Maximilian%22">Bäcker, Claus Maximilian</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Baumann%2C+Kilian‐Simon%22">Baumann, Kilian‐Simon</searchLink><relatesTo>5,6,7</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Esser%2C+Johannes+Niklas%22">Esser, Johannes Niklas</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Koska%2C+Benjamin%22">Koska, Benjamin</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Timmermann%2C+Beate%22">Timmermann, Beate</searchLink><relatesTo>1,2,3,4,8,9</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Verbeek%2C+Nico+Gerd%22">Verbeek, Nico Gerd</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Bäumer%2C+Christian%22">Bäumer, Christian</searchLink><relatesTo>1,2,3,8,10</relatesTo> (AUTHOR)<i> christian.baeumer@uk-essen.de</i>
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  Data: <searchLink fieldCode="JN" term="%22Medical+Physics%22">Medical Physics</searchLink>. Mar2024, Vol. 51 Issue 3, p2277-2292. 16p.
– Name: Subject
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  Data: <searchLink fieldCode="DE" term="%22Ionization+chambers%22">Ionization chambers</searchLink><br /><searchLink fieldCode="DE" term="%22Photon+beams%22">Photon beams</searchLink><br /><searchLink fieldCode="DE" term="%22Radiation+dosimetry%22">Radiation dosimetry</searchLink><br /><searchLink fieldCode="DE" term="%22Reciprocity+theorems%22">Reciprocity theorems</searchLink><br /><searchLink fieldCode="DE" term="%22Absorbed+dose%22">Absorbed dose</searchLink><br /><searchLink fieldCode="DE" term="%22Protons%22">Protons</searchLink><br /><searchLink fieldCode="DE" term="%22Proton+therapy%22">Proton therapy</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Background: A Faraday cup (FC) facilitates a quite clean measurement of the proton fluence emerging from clinical spot‐scanning nozzles with narrow pencil‐beams. The utilization of FCs appears to be an attractive option for high dose rate delivery modes and the source models of Monte‐Carlo (MC) dose engines. However, previous studies revealed discrepancies of 3%–6% between reference dosimetry with ionization chambers (ICs) and FC‐based dosimetry. This has prevented the widespread use of FCs for dosimetry in proton therapy. Purpose: The current study aims at bridging the gap between FC dosimetry and IC dosimetry of proton fields delivered with spot‐scanning treatment heads. Particularly, a novel method to evaluate FC measurements is introduced. Methods: A consistency check is formulated, which makes use of the energy balance and the reciprocity theorem. The measurement data comprise central‐axis depth distributions of the absorbed dose of quasi‐monochromatic fields with a width of about 28.5 cm and FC measurements of the reciprocal fields with a single spot. These data are complemented by a look‐up of energy‐range tables, the average Q‐value of transmutations, and the escape energy carried away by neutrons and photons. The latter data are computed by MC simulations, which in turn are validated with measurements of the distal dose tail and neutron out‐of‐field doses. For comparison, the conventional approach of FC evaluation is performed, which computes absorbed dose from the product of fluence and stopping power. The results from the FC measurements are compared with the standard dosimetry protocols and improved reference dosimetry methods. Results: The deviation between the conventional FC‐based dosimetry and the IC‐based one according to standard dosimetry protocols was −4.7 (±$\pm$ 3.3)% for a 100 MeV field and −3.6 (±$\pm$3.5)% for 200 MeV, thereby agreeing within the reported uncertainties. The deviations could be reduced to −4.0 (±$\pm$ 2.9)% and −3.0 (±$\pm$ 3.1)% by adopting state‐of‐the‐art reference dosimetry methods. The alternative approach using the energy balance gave deviations of only −1.9% (100 MeV) and −2.6% (200 MeV) using state‐of‐the‐art dosimetry. The standard uncertainty of this novel approach was estimated to be about 2%. Conclusions: An alternative concept has been established to determine the absorbed dose of monoenergetic proton fields with an FC. It eliminates the strong dependence of the conventional FC‐based approach on the MC simulation of the stopping‐power and of the secondary ions, which according to the study at hand is the major contributor to the underestimation of the absorbed dose. Some contributions to the uncertainty of the novel approach could potentially be reduced in future studies. This would allow for accurate consistency tests of conventional dosimetry procedures. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Medical Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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      – Type: doi
        Value: 10.1002/mp.16819
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      – Code: eng
        Text: English
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        PageCount: 16
        StartPage: 2277
    Subjects:
      – SubjectFull: Ionization chambers
        Type: general
      – SubjectFull: Photon beams
        Type: general
      – SubjectFull: Radiation dosimetry
        Type: general
      – SubjectFull: Reciprocity theorems
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      – SubjectFull: Absorbed dose
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      – SubjectFull: Protons
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      – SubjectFull: Proton therapy
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              Text: Mar2024
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