ESTRO 2024 - Abstract Book

S3232

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

on materials with significantly higher Z-values and/or densities than those of biological tissues, do not meet these requirements for orthovoltage X-rays. Furthermore, high-performance plastic scintillation (PSD) detectors, which have rather good tissue equivalence[2] [3], face limitations in miniaturization to micrometer scales due to the dopant couple involved in the conversion process (scintillation and wavelength shifting). [4][5] To meet the need of suitable detectors for MRT dosimetry, we have been working on new scintillating detectors based on highly heterogeneous cavities for this application.

Material/Methods:

A highly heterogeneous cavity may mainly consist of a tissue-equivalent organic material. When such a cavity is implemented in a RW3 phantom, it can be considered as a large cavity not disturbing the fluency of the primary photons (the charge particle equilibrium is established). Therefore, the collision Kerma gives a good approximation of the absorbed dose in this (large) cavity. The heterogeneous cavity may also include a small number of scintillating cavities. If these cavities are sufficiently small and spaced apart (in terms of electron range), it can be assumed that i) their direct interaction with the photon beam can be neglected and therefore ii) they mainly detect electrons resulting from the deposition of the dose in the organic material. The response of a detector having such a heterogeneous cavity can be modeled by the combined use of large and small cavity theories. It is expected to have a low energy dependence, thanks to i) the deposition of the dose in the epoxy matrix and ii) the low energy dependence of the mass electron stopping power of the medium even in presence of the nano-scintillators. To establish the proof-of concept for this new detector, we designed and fabricated a prototype with a heterogeneous cavity featuring a sparse scintillating layer a few microns thick based on semiconductor QDots embedded in an epoxy polymer matrix, as shown in Figure 1. The response of this prototype was characterized in MRT conditions on the ID17 biomedical beamline at ESRF. The irradiation dose rate was modified in the range [0.15 – 5.3 kGy/s] by the insertion of PMMA plates in the beam path. It should be mentioned that this insertion also modifying the average beam energy at the detector depth over the range from 121keV to 136keV.

Results: