Properties of IBA Razor Nano Chamber in small-field radiation therapy using 6 MV FF, 6 MV FFF, and 10 MV FFF photon beams

Mari Partanen, Jarkko Niemelä, Jarkko Ojala, Jani Keyriläinen, Mika Kapanen

Research output: Contribution to journalArticleScientificpeer-review

1 Citation (Scopus)

Abstract

BACKGROUND: Small megavoltage photon fields are increasingly used in modern radiotherapy techniques such as stereotactic radiotherapy. Therefore, it is important to study the reliability of dosimetry in the small-field conditions. The IBA Razor Nano Chamber (Nano chamber) ionization chamber is particularly intended for small-field measurements. In this work, properties of the Nano chamber were studied with both measurements and Monte Carlo (MC) simulations.

MATERIAL AND METHODS: The measurements and MC simulations were performed with 6 MV, 6 MV FFF and 10 MV FFF photon beams from the Varian TrueBeam linear accelerator. The source-to-surface distance was fixed at 100 cm. The measurements and MC simulations included profiles, percentage depth doses (PDD), and output factors (OF) in square jaw-collimated fields. The MC simulations were performed with the EGSnrc software system in a large water phantom.

RESULTS: The measured profiles and PDDs obtained with the Nano chamber were compared against IBA Razor Diode, PTW microDiamond and the PTW Semiflex ionization chamber. These results indicate that the Nano chamber is a high-resolution detector and thus suitable for small field profile measurements down to field sizes 2 × 2 cm2 and appropriate for the PDD measurements. The field output correction factors kQclin, Qmsrfclin, fmsr and field OFs ΩQclin, Qmsrfclin, fmsr were determined according to TRS-483 protocol In the 6 MV FF and FFF beams, the determined correction factors kQclin, Qmsrfclin, fmsr were within 1.2% for the field sizes of 1 × 1 cm2-3 × 3 cm2 and the experimental and MC defined field output factors ΩQclin,Qmsrfclin,fmsr showed good agreement.

CONCLUSION: The Nano chamber with its small cavity volume is a potential detector for the small-field dosimetry. In this study, the properties of this detector were characterized with measurements and MC simulations. The determined correction factors kQclin, Qmsrfclin, fmsr are novel results for the NC in the TrueBeam fields.
Original languageEnglish
Pages (from-to)1419-1424
JournalActa Oncologica
Volume60
Issue number11
DOIs
Publication statusPublished - 2021
Publication typeA1 Journal article-refereed

Keywords

  • EGSnrc
  • ionization chamber
  • Monte Carlo simulations
  • relative dosimetry
  • Small-field dosimetry

Publication forum classification

  • Publication forum level 1

ASJC Scopus subject areas

  • Hematology
  • Oncology
  • Radiology Nuclear Medicine and imaging

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