SU‐E‐T‐533: LET Dependence Correction of Radiochromic Films for Application in Low Energy Proton Irradiation

Abstract

Purpose:Many cell irradiation experiments with low‐energy laser‐driven ions rely on radiochromic films (RCF), because of their dose‐rate independent response and superior spatial resolution. RCF dosimetry in low‐energy ion beams requires a correction of the LET dependent film response. The relative efficiency (RE), the ratio of photon to proton dose that yields the same film darkening, is a measure for the film's LET dependence. A direct way of RE determination is RCF irradiation with low‐energy mono‐energetic protons and hence, well‐defined LET. However, RE is usually determined using high energy proton depth dose measurements where RE corrections require knowledge of the average LET in each depth, which can be either track (tLET) or dose (dLET) averaged. The appropriate LET concept has to be applied to allow a proper film response correction.Methods:Radiochromic EBT2 and EBT3 films were irradiated in clinical photon and proton beams. For each depth of the 200 MeV proton depth dose curve, tLET and dLET were calculated by special user routines from the Monte Carlo code FLUKA. Additional irradiations with mono‐energetic low energy protons (4–20 MeV) serve as reference for the RE determination.Results:The difference of dLET and tLET increases with depth, with the dLET being almost twice as large as the tLET for the maximum depth. The comparison with mono‐energetic measurements shows a good agreement of the RE for the dLET concept, while a considerably steeper drop in RE is observed when applying the tLET.Conclusion:RCF can be used as reference dosimeter for biomedical experiments with low‐energy proton beams if appropriate LET corrections are applied. When using depth dose measurements from clinical proton accelerators for these corrections, the concept of dLET has to be applied.Acknowledgement:This work was funded by the DFG Cluster of Excellence ‘Munich‐Centre for Advanced Photonics’ (MAP).This work was funded by the DFG Cluster of Excellence Munich‐Centre for Advanced Photonics (MAP).