SU-E-I-85: Evaluation of a Solid-State Dosimeter Module for Measuring Nuclear Medicine Radionuclides

A recently introduced solid-state dosimeter module (UDOS001, Teledyne Microelectronic Technologies, Los Angeles, CA) requires only external power (e.g., from two nine-volt batteries in series) and a battery- powered data recorder to assemble a compact, portable dosimeter. This device was developed for radiation detection and monitoring of a wide range of radiation types. It has a nominal minimum energy of 100 keV. The present study sought to determine its suitability for measuring the dose from radionuclides used in nuclear medicine.

Three radionuclides (initially 4.77 mCi of F-18, 3.86 mCi of I-131, and 12.4 mCi of Tc-99m) were measured at a distance of one meter and at several different angles of incidence. The most sensitive analog output of the dosimeter was digitized by a battery-powered data logging device (Track-It 5VDC, Monarch Instrument, Amherst NH). These data were transferred from the data logger into a Windows 7 personal computer, formatted as an Excel 2010 spreadsheet and converted from voltage to dose using the manufacturer's nominal calibration factor of 14 urad/19.5 mV step. The dose rate was determined from the slope of a linear fit to the cumulated dose as a function of time.

The nominal calibration of the dosimeter gives dose rate measurements that are close to published gamma ray dose rate constants for these radionuclides (0.65 vs. 0.70, 0.25 vs. 0.28, and 0.071 vs. 0.078 mrad/mCi-hr respectively). The angular dependence of the response is greater at 140 keV than at 511 keV, but an acceptance angle of at least 90 degrees has uniform response with all three radionuclides.

A better calibration factor would be 0.154 urad/19.5 mV step at these gamma ray energies. This dosimeter can be used to measure the dose from common radionuclides used in nuclear medicine.