Cerenkov free micro-dosimetry in small-field radiation therapy technique

Abstract

Purpose: Optical fiber-based scintillating dosimetry is the most recent promising technique owing to the miniature size dosimeter and quality measurement in modern radiation therapy treatment. Despite several advantages, the major issue of using scintillating dosimeters is the Cerenkov effect and predominantly requires extra measurement corrections. Therefore, this work highlighted a novel micro-dosimetry technique to ensure Cerenkov-free measurement in radiation therapy treatment protocol by investigating several dosimetric characteristics.

Methods: A micro-dosimetry technique was proposed with the performance evaluation of a novel infrared inorganic scintillator detector (IR-ISD). The detector essentially consists of a micro-scintillating head based on IR-emitting micro-clusters with a sensitive volume of 1.5x10-6 mm3. The proposed system was evaluated under the 6 MV LINAC beam used in patient treatment. Overall measurements were performed using IBATM water tank phantoms by following TRS-398 protocol for radiotherapy. Cerenkov measurements were performed for different small fields from 0.5×0.5 cm2 to 10x10cm2 under LINAC. In addition, several dosimetric parameters such as percentage depth dose (PDD), high lateral resolution beam profiling, dose linearity, dose rate linearity, repeatability, reproducibility, and field output factor (FOC) were investigated to realize the performance of the novel detector.

Results: This study highlighted a complete removal of the Cerenkov effect using a point-like miniature detector, especially for small field radiation therapy treatment. Measurements demonstrated that IR-ISD has acceptable behavior with dose rate variability (maximum standard deviation ~ 0.18%) for the dose rate of 20 cGy/s to 1000 cGy/s. An entire linear response(R2=1) was obtained for the dose delivered within the range of 4cGy to 1000 cGy, using a selected field size of 1×1 cm². Perfect repeatability (max 0.06 % variation from average) with day-to-day reproducibility (0.10% average variation) was observed. PDD profiles obtained in the water tank present almost identical behavior to the reference dosimeter with a build-up maximum depth dose at 1.5 cm. The small field of 0.5 × 0.5 cm² profiles have been characterized with a high lateral resolution of 100 µm.

Conclusions: Unlike recent plastic scintillation detector(PSD) systems (e.g., exradin W1/W2), the proposed micro-dosimetry system in this study requires no Cerenkov corrections and showed efficient performance for several dosimetric parameters. Therefore, it is expected that considering the detector correction factors, the IR-ISD system can be a suitable dose measurement tool, such as in small-field dose measurements, high and low gradient dose verification, and, by extension, in microbeam radiation and FLASH radiation therapy.