Results: The resulting depth dose c

Results: The resulting depth dose curves were normalized to their 100% dose at the reference depth of 3 cm. We obtained the skin doses with the extrapolation chamber and with TOPAS. For the experimental approach this resulted in 79.7 _ 0.3%, 86.0 _ 0.6%, and 87.1 _ 0.1% for the proton energies 100, 150, and 226.7 MeV, respectively. The results for TOPAS were 80.1 _ 0.2% (100 MeV), 87.1 _ 0.5% (150 MeV), and 86.9 _ 0.4% (226.7 MeV), respectively. Based on the experimental results of the skin dose, we provided a clinically relevant surface extrapolation factor for the common measurement methods. This allows the result of the first measurement depth of a detector to be scaled to the dose at the skin depth. Most practical would be the use of the surface extrapolation factor for the PPC05 chamber, due to its direct reading, the wide availability in clinics and the low uncertainties. The calculated factors were 0.986 _ 0.004 for 100 MeV, 0.961 _ 0.008 for 150 MeV, and 0.963 _ 0.003 for 226.7 MeV.