A Novel Micro-Dosimetry Technique to Advance Small-Field Radiation Therapy Treatment

Abstract

<h3>Purpose/Objective(s)</h3> Optical fiber-based scintillating dosimetry is the most recent promising technique in modern radiation therapy owing to the miniature size, high sensitivity, flat energy dependency, etc. Despite several advantages, the major issue of using scintillating dosimeters is the Cerenkov contamination and predominantly requires extra measurement corrections. Therefore, this work highlighted a novel micro-dosimetry technique to ensure Cerenkov-free measurement and quality treatment. <h3>Materials/Methods</h3> A micro-dosimetry technique was proposed based on a novel infrared inorganic scintillator detector (IR-ISD). The detector essentially consists of a micro-scintillating head with a sensitive volume of 1.5 × 10⁻⁶ mm³ integrated with optical fiber. The proposed system was evaluated under the 6/15 MV LINAC beam as well as 320KV- ¹⁹²Ir Brachytherapy (BT) source used in patient treatment. Overall measurements were performed using IBA^TM water tank phantoms by following TRS-398 protocol for radiotherapy and TG43U1 recommendations for BT. Cerenkov measurements were performed for different small fields from 0.5 × 0.5 cm² to 10 × 10cm² under LINAC as well as till 0.25cm distance from the BT source. In addition, several dosimetric parameters such as PDD, beam profiling, field output factor, dose linearity, dose rate linearity, repeatability, and scintillation stability were investigated to verify the device's performance. Finally, a comparative study is shown using Monte-Carlo (MC) simulation, reference dosimeters (microDiamond and film), and data from recent literature. <h3>Results</h3> This study highlighted a complete removal of the Cerenkov effect using a point-like miniatured detector, especially for small-field beam treatment. Measurements demonstrated that IR-ISD has acceptable behavior with dose rate variability (maximum standard deviation ∼ 0.15%) for the dose rate of 20 cGy/s to 1000 cGy/s. An entire linear response (R²=1) was obtained with the dose delivered in the range of 4cGy to 1000 cGy, independently of the field size selected from 4 × 4 cm² to 0.5 × 0.5 cm². Perfect repeatability (0.15 % variation from average) and day-to-day reproducibility (0.25% variation) was observed. PDD profiles present accurate dose distribution with almost identical behavior to the reference dosimeter and simulation results (<1.5% variation). The small field of 0.5 × 0.5 cm² profile (inline & crossline) has been measured to characterize convolution effect and source penumbra. Eventually, in BT, a comparison with MC simulations shows that measurement agrees within 0.65% till 0.25 cm source-to-detector distance. <h3>Conclusion</h3> Unlike recent PSD systems (e.g., exradin W1/W2), the proposed micro-dosimetry system requires no Cerenkov corrections and showed efficient performance for several dosimetric measurements. Therefore, the novel IR-ISD detector could be a quality tool for small-field dose verification (e.g., in SRS, SBRT, IMRT, etc.), intra-beam characterizations, and BT treatment plan.