Accuracy of small-field high energy photon using plastic scintillation detector in heterogenous media compared with model-based algorithm calculation

Abstract

Some radiotherapy techniques such as stereotactic body radiotherapy (SBRT) has the challenges in small field dosimetry in heterogenous media. This study aims at evaluating the accuracy of W2 plastic scintillation detector (PSD) compared with the calculation from algorithms for small-field high energy photon in heterogenous media. The characteristics of W2-PSD were studied. The percentage depth dose (PDD) of 6 FFF and 10 FFF with various field sizes ranging from 1x1 to 4x4 cm2 were measured in solid water phantom with low-density inhomogeneities slabs of air (Styrofoam) and lung (cork) and high-density inhomogeneity slab of aluminum. The characteristics of W2 plastic scintillator were very good in terms of repeatability and linearity. The maximum deviation of repetition rate and energy dependence were within 1%. The PDD results showed the same trend in both air and lung heterogeneity which presented the dose drop in heterogeneous media region and re-buildup after that. On the contrary, in aluminum heterogenity the dose increased at upper interface. The large difference of PDD curve inside heterogeneous media was presented with higher energy, smaller field size and lower density medium. From the SBRT clinical application results, the differences between measured and calculated doses were within 5%. Hence, the W2-PSD is possible to be used for small-field dosimetry in heterogeneous media according to IAEA TRS 430.