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Related Experiment Video

Updated: Mar 2, 2026

Full-field Strain Measurements for Microstructurally Small Fatigue Crack Propagation Using Digital Image Correlation Method
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SU-E-T-230: Field Factor Verification in Small Fields.

Y Jia1, H Zhang1, C Desrosiers1

  • 1Indiana University- School of Medicine, Indianapolis, IN.

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|May 19, 2017
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Summary
This summary is machine-generated.

The correction factor K improves small field dosimetry accuracy in radiosurgery and IMRT. Applying K to various detectors, including an extrapolation ion chamber, matched field factors within 2.2%.

Keywords:
DosimetryField sizeField theoryImage sensorsIntensity modulated radiation therapyIonization chambersParticle beam detectorsPhotonsRadiosurgery

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Area of Science:

  • Medical Physics
  • Radiotherapy Dosimetry

Background:

  • Small field dosimetry in radiosurgery and IMRT presents challenges due to detector size and electronic disequilibrium.
  • Published correction factors (K) exist for limited detectors and energies, necessitating further validation.

Purpose of the Study:

  • To investigate the validity of the correction factor K for various small field detectors.
  • To explore the use of an extrapolation ion chamber with the reciprocity theorem for small field dosimetry.

Main Methods:

  • Measurements were performed using IBA SFD, PTW diodes, PTW pinpoint, Standard Imaging diode, and a Nuclear Associate extrapolation chamber.
  • Output factors for square fields (1x1 to 10x10 cm²) were measured for 6 and 16 MV Varian beams in a water phantom.
  • Published correction factors (K) were applied, and a K value was derived for the extrapolation chamber via modeling.

Main Results:

  • Significant output variations (±7.0%) were observed among detectors for field sizes ≤ 3x3 cm², converging for larger fields.
  • The extrapolation chamber's output initially differed from diode/pinpoint measurements for both 6 and 16 MV beams.
  • After applying the correction factor K, field size factors agreed within ±2.2% across all detectors and field sizes.

Conclusions:

  • The correction factor K effectively reconciles field factors from different detectors within ±2.2%.
  • An extrapolation ion chamber, when modeled mathematically, provides comparable field factors to other detectors for small fields.