Small Scale Inorganic X-Ray Detector For Dosimetry In Radiotherapy And Brachytherapy

With the development of high accuracy treatment technique in radiotherapy, e.g. VMAT and SBRT, dose measurement and distribution in TPS (treatment planning system) must be characterized meticulously. To ensure an accurate beam modeling process, dosimeters with high accuracy and spatial resolution are needed especially for treatment using small fields, related to lesion observed in early stage cancer treatment or treatment with high dose gradient like in brachytherapy or SBRT. In this context, the idea of this research work is aimed at developing a novel detectors of sub-millimeter dimension based on inorganic scintillator. We developed a simple and small-scale inorganic scintillating X-ray detector (ISD) of 200 μm diameter with a sensitive volume of 100 μm3. The detector was tested on a linear accelerator tuned at 6 MV/15MV and under Brachytherapy with source Ir-192 used in the patient treatment protocol. The article presents the performances of the detector in terms of linearity, reliability, reproducibility and spatial resolution. Beam profiling down to 0.5 x 0.5 cm2 field at high spatial resolution was performed. In addition, the real-time X-ray detector demonstrated that stem effect has negligible effect for fields smaller than 3x3 cm2. A comparative study is shown using a reference microdiamond dosimeter and data from recent literature. ISD also used to monitor real time dose measurement, dwell positions and dwell time measurement during Brachytherapy (BT) source tracking. This study is highlighting the drastic decrease of convolution effect using a point-like detector, especially for low dimension LINAC beam characterization. The detector provides an entire linear response with the dose in the 0 to 500 cGy range, independently of the field size selected from 10 x 10 cm2 down to 0.5 x 0.5 cm2. The detector presents a perfect repeatability with day-to-day reproducibility (0.5%) and confirmed that it is almost stem effect free specially below 3x3 cm2 field. PDD profiles obtained in water with both detectors’ present identical behavior with a build-up maximum depth dose at 15 mm. Low dimension 0.5 x 0.5 cm2 field profiles have been characterized and field cross profile presents a Gaussian-like shape. ISD detector showed a better accuracy than reference detector due to a lower convolution effect induced by its smallest sensitive volume. In brachytherapy, output linearity and reproducibility of ISD maintained at the acceptable range (<1%) and high accuracy obtained during source tracking. All the results under LINAC presented here show that the developed detector can be an efficient candidate to improve beam characterization and treatment modeling process, hence conform quality assurance. In BT, ISD can precisely detect relative dwell time and dwell positions, hence can be used as patient safety monitoring.