This report examines the recommendations of The International Commission for Radiation Units and Measurements, ICRU 50 and a typical interpretation of them. It hypothesises that there is a small identifiable group of patients that may be at risk of long term damage due to current radiotherapy treatment to the breast.

The report emphasises the variation in dose obtained when the whole volume of the irradiated breast is considered. The dose distribution beyond the central contour and the effect of lung density is analysed. Even if three-dimensional planning and inhomogeneity correction factors are not available, consideration must be given to their significance.

This report acknowledges that the ICRU reference point is a much-needed method of comparing radiotherapy treatments between hospitals, but points out that it was not intended to be a means of determining dosimetry, despite the suggestion that it may be advantageous if its relative dose is 100%.

The report concludes that there should be greater awareness and attention paid to the recommendation that heterogeneity should be within +7 and −5% of the prescribed dose.