Miniaturized scintillator dosimeter for small field radiation therapy

Abstract

The concept of a miniaturized inorganic scintillator detector is demonstrated in the analysis of the small static photon fields used in external radiation therapy. Such a detector is constituted by a 0.25 mm diameter and 0.48 mm long inorganic scintillating cell (1.6 × 10−5 cm3 detection volume) efficiently coupled to a narrow 125 μm diameter silica optical fiber using a tiny photonic interface (an optical antenna). The response of our miniaturized scintillator detector (MSD) under 6 MV bremsstrahlung beam of various sizes (from 1 × 1 cm2 to 4 × 4 cm2) is compared to that of two high resolution reference probes, namely, a micro-diamond detector and a dedicated silicon diode. The spurious Cerenkov signal transmitted through our bare detector is rejected with a basic spectral filtering. The MSD shows a linear response regarding the dose, a repeatability within 0.1% and a radial directional dependence of 0.36% (standard deviations). Beam profiling at 5 cm depth with the MSD and the micro-diamond detector shows a mismatch in the measurement of the full widths at 80% and 50% of the maximum which does not exceed 0.25 mm. The same difference range is found between the micro-diamond detector and a silicon diode. The deviation of the percentage depth dose between the MSD and micro-diamond detector remains below 2.3% within the first fifteen centimeters of the decay region for field sizes of 1 × 1 cm2, 2 × 2 cm2 and 3 × 3 cm2 (0.76% between the silicon diode and the micro-diamond in the same field range). The 2D dose mapping of a 0.6 × 0.6 cm2 photon field evidences the strong 3D character of the radiation-matter interaction in small photon field regime. From a beam-probe convolution theory, we predict that our probe overestimates the beam width by 0.06%, making our detector a right compromise between high resolution, compactness, flexibility and ease of use. The MSD overcomes problem of volume averaging, stem effects, and despite its water non-equivalence it is expected to minimize electron fluence perturbation due to its extreme compactness. Such a detector thus has the potential to become a valuable dose verification tool in small field radiation therapy, and by extension in Brachytherapy, FLASH-radiotherapy and microbeam radiation therapy.

Characterization of a miniaturized scintillator detector for time-resolved treatment monitoring in HDR-brachytherapy

“…As an alternative approach, the concept of a miniaturized scintillator detector (MSD) has been recently introduced from the harnessing of inorganic scintillators to a narrow 125-µm diameter silica fiber with a microfabricated photonic antenna (Suarez et al 2019). A MSD with a detection volume as small as 0.016 mm 3 (0.25-mm diameter and 0.48-mm long ellipsoid) has been demonstrated in external beam radiotherapy (Gonod et al 2021). The MSD has been shown to overcome the stem effect, and despite its water nonequivalence (both scintillator and fiber), it minimizes electron fluence perturbation due to its extreme compactness.…”

Six‐probe scintillator dosimeter for treatment verification in HDR‐brachytherapy

“…The overall fabrication process is detailed in Refs. [29, 30]. The MPD is locally enlarged to diameters around 320 microns by the presence of the scintillating cells (see Figure 1c).…”

Radioluminescence imaging feasibility for robotic radiosurgery field size quality assurance

“…Using such small field sizes, accurate and reliable dose measurements methods are required. 7 , 8 , 9 , 10 , 11 , 12 , 13 …”

“…The iris collimator creates fields of polygon with different sizes from 5 mm to 60 mm. Using such small field sizes, accurate and reliable dose measurements methods are required 7–13 …”

“…Using such small field sizes, accurate and reliable dose measurements methods are required. [7][8][9][10][11][12][13] Radiochromic films are the gold standard for 2D verification of dose distributions during radiation therapy and for many geometric quality assurance (QA) tests.…”