Technical Note: Empirical altitude correction factors for well chamber measurements of permanent prostate and breast seed implant sources

Abstract

This work presents altitude correction factors for three permanent implant brachytherapy seed models in clinical use. This will allow clinics to utilize model-specific factors, reducing systematic errors in their air-kerma strength verifications.

Effect of well chamber altitude pressure corrections for cesium Blu 131Cs and CivaDot 103Pd brachytherapy sources

“…These points may have caused a small increase in the overall uncertainty due to a slightly worse curve fit, but the total uncertainties as described in Section V were still comparable to other publications of similar experiments. 7,8 The calculated correction coefficients are given in Table 2 for pressure measurements in mmHg for historical purposes and in Table 3 with coefficients given for pressure measurements in kPa. Note that the k 2 values are the same for both pressure scales, as the rate of change in response with varying pressure does not change, but the k 1 value does change to reflect the difference in absolute pressure value at the points of data collection.…”

“…This leads to a difference in calculated correction factor of 0.43%, most likely caused by the directionality of the CivaDot source. Comparing against the other commercially available 103 Pd source, the IsoAid Advantage, would yield the same difference in correction factor as the IsoAid Advantage and the Theraseed 200 sources have the same correction coefficients 8 …”

“…As previously discussed by Watt et al., although the difference between correction factors for different sources are generally small in magnitude, using the incorrect coefficients may result in a systematic offset of calculated air‐kerma strengths 8 . Prior to this work, clinics using the Cesium Blu source were encouraged to use the correction coefficients for the SourceTech STM 125I source, which were calculated by Griffin et al 7 .…”

“…Comparing against the other commercially available 103 Pd source, the IsoAid Advantage, would yield the same difference in correction factor as the IsoAid Advantage and the Theraseed 200 sources have the same correction coefficients. 8 These differences were calculated for altitudes near Denver,CO (1620 m elevation);differences at higher elevations, such as Mexico City, Mexico, would be higher. Correction coefficients used for comparison were taken from either Griffin et al 7 or Watt et al 8…”

“…The purpose of this work is to provide values for several sources that are in use clinically, but which are lacking published correction coefficients, as well as to present findings on factors that may effect the altitude response of the sources. The coefficients depend on the unit of pressure used for measurement and have usually been given for measurements in Torr, valid as well for mmHg measurements due to the equivalence of the units 7,8 . Coefficients in this work will be given for both kPa and, for the sake of history and comparison, in Torr/mmHg.…”