Plastic scintillator dosimetry in regions with restricted secondary electron equilibrium

Problem: Dosimetry in regions without secondary electron equilibrium (SEE) is complicated because the measuring probe causes particle flux disturbances which are difficult to correct. Non-SEE conditions are often combined with steep dose gradients and/or changes in the particle energy spectra. Solution: Tissue substituting plastic scintillators with high spatial resolution provide a solution for these problems. The material allows probe designs adjusted to the requested measuring situation. Results: Plastic scintillators were successfully employed for the interface dosimetry (internal inhomogeneities, build-up regions) at external photon beams, in brachytherapy dosimetry (HDR-afterloading, eye-plaque optimization) and in proton beam dosimetry. Basing on experiences with specially designed phantoms and multi-detector arrays, the physical possibilities and limitations of scintillation dosimetry are discussed for the clinically used particle energies. Conclusion: The scintillator is an adequate detector for the dosimetry under non-SEE conditions