Surface dose measurements in clinical photon beams.

Surface dose measurements have been made with different dosemeters routinely in clinical practice such as thermoluminescence (TL) dosemeters of different thicknesses or Si-diodes. The results obtained are compared with surface dose measurements made with an extrapolation chamber. TL-dosemeters with a thickness of 0.13 mm are shown to be suitable for skin dose estimations and accurate within 5% if appropriate correction factors are applied. The measured dose obtained for 60Co, 6 MV and 21 MV x-rays should, for these dosemeters, be multiplied by 0.82, 0.90 and 1.0 respectively to obtain the correct surface dose. Thicker dosemeters are inaccurate because they overestimate the surface dose inside the beam and underestimate it outside the beam and the deviation from the correct dose varies with irradiation geometry.