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Tommy Knöös

Sjukhusfysiker

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Comparative dosimetry of diode and diamond detectors in electron beams for intraoperative radiation therapy

Författare

  • Peter Björk
  • Tommy Knöös
  • Per Nilsson

Summary, in English

The aim of the present study is to examine the validity of using silicon semiconductor detectors in degraded electron beams with a broad energy spectrum and a wide angular distribution. A comparison is made with diamond detector measurements, which is the dosimeter considered to give the best results provided that dose rate effects are corrected for. Two-dimensional relative absorbed dose distributions in electron beams (6-20 MeV) for intraoperative radiation therapy (IORT) are measured in a water phantom. To quantify deviations between the detectors, a dose comparison tool that simultaneously examines the dose difference and distance to agreement (DTA) is used to evaluate the results in low- and high-dose gradient regions, respectively. Uncertainties of the experimental measurement setup (+/- 1% and +/- 0.5 mm) are taken into account by calculating a composite distribution that fails this dose-difference and DTA acceptance limit. Thus, the resulting area of disagreement should be related to differences in detector performance. The dose distributions obtained with the diode are generally in very good agreement with diamond detector measurements. The buildup region and the dose falloff region show good agreement with increasing electron energy, while the region outside the radiation field close to the water surface shows an increased difference with energy. The small discrepancies in the composite distributions are due to several factors: (a) variation of the silicon-to-water collision stopping-power ratio with electron energy, (b) a more pronounced directional dependence for diodes than for diamonds, and (c) variation of the electron fluence perturbation correction factor with depth. For all investigated treatment cones and energies, the deviation is within dose-difference and DTA acceptance criteria of +/- 3% and +/- 1 mm, respectively. Therefore, p-type silicon diodes are well suited, in the sense that they give results in close agreement with diamond detectors, for practical measurements of relative absorbed dose distributions in degraded electron beams used for IORT.

Avdelning/ar

  • Medicinsk strålningsfysik, Lund

Publiceringsår

2000

Språk

Engelska

Sidor

2580-2588

Publikation/Tidskrift/Serie

Medical Physics

Volym

27

Issue

11

Dokumenttyp

Artikel i tidskrift

Förlag

American Association of Physicists in Medicine

Ämne

  • Biophysics

Nyckelord

  • diamond detector
  • silicon diode
  • intraoperative radiation therapy
  • electron beam dosimetry
  • dose distribution analysis

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 0094-2405