The Bland-Altman analysis: Does it have a role in assessing radiation dosimeter performance relative to an established standard?

Bland-Altman analysis is used to compare two different methods of measurement and to determine whether a new method of measurement may replace an existing accepted ‘gold standard’ method. In this work, Bland-Altman analysis has been applied to radiation dosimetry to compare the PTW Markus and Roos parallel plate ionisation chambers and a PTW PinPoint chamber against a Farmer type ionisation chamber which is accepted as the gold standard for radiation dosimetry in the clinic. Depth doses for low energy x-rays beams with energies of 50, 75 and 100 kVp were measured using each of the ionisation chambers. Depth doses were also calculated by interpolation of the data in the British Journal of Radiology (BJR) Report 25. From the Bland-Altman analysis, the mean dose difference between the two parallel plate chambers and the Farmer chambers was 1% over the range of depths measured. The PinPoint chamber gave significant dose differences compared to the Farmer chamber. There were also differences of up to 12% between the BJR Report 25 depth doses and the measured data. For the Bland-Altman plots, the lines representing the limits of agreement were selected to be a particular percentage agreement e.g. 1 or 2%, instead of being based on the standard deviation (σ) of the differences. The Bland-Altman statistical analysis is a powerful tool for making comparisons of ionisation chambers with an ionisation chamber that has been accepted as a ‘gold standard’. Therefore we conclude that Bland-Altman analysis does have a role in assessing radiation dosimeter performance relative to an established standard.