TH-A-204-02: Part II - Worldwide Radiation Metrology



The ICRU is currently finalizing a report on key data for radiation dosimetry. This multi-year review has resulted in a number of recommendations regarding “fundamental” data that are used in dosimetry related to radiation therapy. This educational session will explain the background for the ICRU committee's work, the content and conclusions of the report and the impact on outputs, including NIST primary standards, ADCL calibration coefficients and clinical reference dosimetry. Parameters and beam modalities potentially affected by this report include:

The mean excitation energy, I, for graphite, air, and water, The average energy required to create an ion pair in dry air (commonly referred to as W/e), The uncertainty in the determination of air kerma in kV x-rays The absolute value of Co-60 and Cs-137 primary standards and the dissemination of calibration coefficients, The determination of air kerma strength for Ir-192 HDR brachytherapy sources Ion chamber kQ factors for linac MV beams Ion chamber kQ factors for proton beams.

The changes in reference dosimetry that would result from adoption of the ICRU recommendations are of the order of 0.5% to 1%, an effect that will not impact clinical dose delivery but will be detectable in the clinical setting.

This session will also outline how worldwide metrology is coordinated through the Convention of the Meter and therefore how the international dosimetry community will proceed with adopting these recommendations so that uniformity from country to country in reference dosimetry is maintained. Timelines and communications methods will also be discussed to ensure that users, such as clinical medical physicists, are not surprised when their chamber's calibration coefficient apparently changes.

Learning Objectives:

  • 1.Understand the background for the ICRU committee's work on key dosimetry data.
  • 2.Understand the proposed changes to key data and the impacts on reference dosimetry.
  • 3.Understand the methodology and timeline for adoption of the ICRU recommendations.