TU‐A‐116‐09: Real‐Time Plastic Scintillation Dosimeter for Fluoroscopically‐Guided Interventional Procedures

Abstract

Purpose: To monitor and measure, in real‐time, patient skin dose during fluoroscopically‐guided interventional (FGI) procedures using a novel plastic scintillation dosimeter (PSD). Methods: A clear optical fiber of 1 mm diameter, 10 m long, is optically coupled to a plastic scintillation fiber (BCF‐60) of 1 mm diameter, 10 mm long. On its other end, the clear fiber is connected to an avalanche photodiode, APD (C4777‐01, Hamamatsu). An electrometer collects the APD charge and displays live graph and dose values. Initial calibration is achieved with a NRC calibrated Farmer‐type ionization chamber (Exradin A12, Standard Imaging). The PSD and the chamber are set on an Allura Xper Fd10/10 (Philips) intervention table at the Air Kerma reference point, 150 mm below isocentre. In compliance with TG‐125 data collection methodology, slabs of solid water are gradually added over the instruments. In order to preserve image quality, the automatic controls increase tube current and kVp accordingly. Acquisitions are made in both cine‐fluorography and fluoroscopy operation modes, at 15 frames/s. Measurements were repeated by replacing the solid water by an Alderson RANDO phantom, with image intensifier as close as possible of the surface to replicate clinical protocols. Results: The calibration curves indicate that PSD response is linear below 80 kVp, but exhibits a quadratic behavior above, with a rate of 20–40 pA/mGy over Air Kerma Rate range of 0.10–16 mGy/s. The PSD can read dose rate as low as 1.7 mGy/s ± 5 %. However, uncertainties rise above 10 % for dose rate less than 1 mGy/s. Phantom measurements indicate that the dosimeter is accurate for clinical applications. Conclusion: A PSD has been calibrated and tested in order to monitor and measure low dose rates involved in FGI procedures in real‐time. The next steps will include Monte Carlo calculations to assess accuracy before starting clinical procedures.