Characterization of an inorganic scintillator for small‐field dosimetry in MR‐guided radiotherapy

Abstract

Introduction Aim of this study is to dosimetrically characterize a new inorganic scintillator designed for magnetic resonance‐guided radiotherapy (MRgRT) in the presence of 0.35 tesla magnetic field (B). Methods The detector was characterized in terms of signal to noise ratio (SNR), reproducibility, dose linearity, angular response, and dependence by energy, field size, and B orientation using a 6 MV magnetic resonance (MR)‐Linac and a water tank. Field size dependence was investigated by measuring the output factor (OF) at 1.5 cm. The results were compared with those measured using other detectors (ion chamber and synthetic diamond) and those calculated using a Monte Carlo (MC) algorithm. Energy dependence was investigated by acquiring a percentage depth dose (PDD) curve at two field sizes (3.32 × 3.32 and 9.96 × 9.96 cm2) and repeating the OF measurements at 5 and 10 cm depths. Results The mean SNR was 116.3 ± 0.6. Detector repeatability was within 1%, angular dependence was <2% and its response variation based on the orientation with respect to the B lines was <1%. The detector has a temporal resolution of 10 Hz and it showed a linear response (R2 = 1) in the dose range investigated. All the OF values measured at 1.5 cm depth using the scintillator are in accordance within 1% with those measured with other detectors and are calculated using the MC algorithm. PDD values are in accordance with MC algorithm only for 3.32 × 3.32 cm2 field. Numerical models can be applied to compensate for energy dependence in case of larger fields. Conclusion The inorganic scintillator in the present form can represent a valuable detector for small‐field dosimetry and periodic quality controls at MR‐Linacs such as dose stability, OFs, and dose linearity. In particular, the detector can be effectively used for small‐field dosimetry at 1.5 cm depth and for PDD measurements if the field dimension of 3.32 × 3.32 cm2 is not exceeded.

Characterization of Inorganic Scintillator Detectors for Dosimetry in Image-Guided Small Animal Radiotherapy Platforms

“…The scintillator material's effective atomic number (Zeff) is 30.79, and its density is equal to 3.4 g/cm 3 . The detector has a high scintillator light yield and a reduced Cerenkov effect, resulting in a higher signal-to-noise ratio (SNR) [26], compared with those of similar size using organic scintillators.…”

“…Scintillators (organic and inorganic) have been identified as reliable detectors for realtime dosimetry in several radiotherapy applications [23][24][25][26]. One of the challenges for their use as dosimeters is the presence of Cerenkov radiation that is produced during irradiation in the fibre itself, which appears as noise to the detectors' signal associated with the absorbed dose.…”

“…Sample optical filtering and chromatic removal are among the most commonly implemented procedures [27]. Cerenkov radiation seems to have less prominence in the response of inorganic scintillators due to their higher light yield [26]. Despite the increased popularity of scintillator detectors for dosimetry among different energy ranges, including those of IGSARTP [28], characterization of the energy dependence in the medium-energy X-ray range has been rarely reported in the literature.…”

Artificial Intelligence in magnetic Resonance guided Radiotherapy: Medical and physical considerations on state of art and future perspectives

“…In an online adaptive MRgRT treatment, AI solutions for patient specific QA would have a high clinical impact, especially considering the fact that the QA result has to be provided in a few seconds, while the patient is waiting in treatment position [177,178]. In vivo dosimetry systems based on inorganic scintillators are under development to provide real-time dosimetric information during beam delivery, but they are still far from clinical implementation also because they are not able to provide 3D measurements at this stage of development [179,180]. The AI growth is leading the automatization of a lot of QA processes in conventional RT, and it is reasonable to assume that most of these innovations will soon be implemented in MRgRT as well, although no dedicated experiences have been published so far.…”

Characterization of Plastic Scintillator Detector for In Vivo Dosimetry in Gynecologic Brachytherapy

“…In a detector with a cylindrical symmetry, such as the PSD of the present study, two principal planes were defined for specifying the angular dependence—the axial plane, which cuts the cylindrical scintillator perpendicular to its axis, and the azimuthal plane, which contains the axis of the cylindrical scintillator. PSDs are assumed to have low axial and azimuthal angular dependence if the ratio of length to diameter is below 5:1 [ 9 ] in comparison with other types of detectors, such as inorganic scintillators [ 10 , 11 ], MOSFET [ 12 ], or diodes [ 13 ]. However, the high dispersion of values for PSDs reported in the bibliography both in the axial plane (range 0.3–5%) [ 14 , 15 , 16 , 17 ] and the azimuthal plane (range 0.6–97%) [ 9 , 15 , 16 , 18 ] suggests that precise characterization of this angular dependence is recommended for clinical dosimetry.…”