SU-E-I-41: Characterization of a Linear Fiber-Optic Coupled Dosimeter

This study investigated the dosimetry performance of a linear fiber-optic coupled dosimeter with a sensitive element varying from 3 to 15 cm in length. The dosimeter is comprised of a tissue equivalent plastic scintillating fiber coupled to a photomultiplier tube (PMT). The sensitive element has a length representative of the dimensions of common adult internal organs and measures the absorbed dose along the entire sensitive length. The measurement of absorbed dose in one dimensional space provides a more meaningful measure of the average organ dose compared to current dosimeters which evaluate the dose at a small volume, or point inside the organ.

A fiber-optic coupled dosimetry system was modified by increasing the linear dimension of the sensitive element to sizes ranging from 3 to 15 cm. A FOC element providing a variable output as a function of exposed dosimeter length, beam energy, depth, and beam intensity, was characterized for various exposure parameters relating to Computed Tomography. A clinical x-ray tube, with half-value layer of 5.60 mm Al at 120 kVp, was used to evaluate the dosimeter response to beam energy, intensity, beam quality, and exposed length.

The system consistently demonstrated linearity with tube output and length of the sensitive element and offering excellent sensitivity and reproducibility. The dosimeter also demonstrated a linear response of detected counts to length of scintillation material in the x-ray field over the range of interest. The sensitivity with respect to energy and depth showed a positive linear dependence. An 8% variation in sensitivity across a 12 cm depth was observed within a soft tissue-equivalent medium.

The system allows for rapid and accurate average organ dose measurements relevant to x-ray sources within the diagnostic energy range. The response to previously discussed parameters was independent of the sensitive element length.