ABSTRACT
The build-up region and its concomitant skin-sparing effect are one of the most distinct characteristics of megavoltage photon beams. In skin dosimetry, the recommended depth for dose determination varies with the effect considered. The skin/build-up dose is a complex function of many parameters: beam energy, beam modifying devices, immobilization accessories, and couch top in the beam line. The International Commission on Radiological Protection and the International Commission on Radiation Units and Measurements generally recommends skin-dose assessments at 0.07 and 1.0 mm depth for epidermal and dermal effects, respectively. A particularly remarkable application of radiochromic films positioned on a phantom surface is the use of a radiochromic film stack as a three-dimensional build-up dose detector. A. De Puysseleyr et al. compared extrapolation chambers with external beam therapy (EBT2) radiochromic film measurements in flattened and unflattened photon beams at depths beyond 1 mm. EBT2 film had to be carefully positioned on the surface of a phantom due to its asymmetric layer configuration.
