Photon energy readings in OSL dosimeter filters: an application to retrospective dose estimation for nuclear medicine workers

Abstract

This work investigates the applicability of using data from personal monitoring dosimeters to assess photon energies to which medical workers were exposed. Such determinations would be important for retrospective assessments of organ doses to be used in occupational radiation epidemiology studies, particularly in the absence of work history or other information regarding the energy of the radiation source. Monthly personal dose equivalents and filter ratios under two different metallic filters contained in the Luxel+^® dosimeter were collected from Landauer, Inc. from 19 nuclear medicine (NM) technologists employed by three medical institutions, the institution A only performing traditional NM imaging (primarily using ^99m Tc) and institutions B and C also performing positron emission tomography (PET, using ¹⁸F). Calibration data of the Luxel+^® dosimeter for various xray spectra were used to establish ranges of filter ratios from 1.1 to 1.6 for ^99m Tc and below 1.1 for ¹⁸F. Median filter ratios were 1.33 (Interquartile range (IQR), 0.15) for institution A, 1.08 (IQR, 0.16) for institution B, and 1.08 (IQR, 0.14) for institution C. The distributions of these filter ratios were statistically-significantly different between the institution A only performing traditional NM imaging and institutions B and C also performing PET imaging. In this proof-of-concept study, filter ratios from personal monitoring dosimeters were used to assess differences in photon energies to which NM technologists were exposed. Dosimeters from technologists only performing traditional NM procedures mostly showed Al/Cu filter ratios above 1.2, those likely performing only PET in a particular month had filter ratios below 1.1, and those which showed filter ratios between 1.1 and 1.2 likely came from technologists rotating between traditional NM and PET imaging in the same month. These results suggest that it is possible to distinguish technologists who only worked with higher-energy procedures versus those who only worked with other types of NM procedures.

Figure 1.

Aluminum to copper (Al/Cu) filter dose ratios by X-Ray beams (Landauer, Inc).

Figure 2.

Box-and-whisker plot of the distributions of monthly H_p (10) by technologists from institution A (A), from institution B (B), from institution C (C), and grouped per institution (D) in 2015 (with minimum, median, maximum, first quartile Q1 and third quartile Q3).

Figure 3.

Box-and-whisker plot of the distributions of Al/Cu filter ratios from institution A, B and C in 2015 (with minimum, median, maximum, first quartile Q1 and third quartile Q3).

Figure 4.

Distribution of 2015 monthly H_p(10) in function of the corresponding Al/Cu filter ratios from institution A, institution B and institution C.