18F protection issues: Human and γ-camera considerations

ZongJian Cao, James H. Corley, Jerry Allison

Research output: Contribution to journalArticle

3 Scopus citations

Abstract

Objective: Two main issues in protecting radiation workers and the general public from 18F radiation - distance from and lead shielding for an 18F source-were investigated. We also examined the effect of an 18F source on the counting rate of a neighboring γ-camera. Methods: The dose rates of an 18F vial and a water-filled cylinder were measured using an ionization chamber at different distances with or without lead shielding. In addition, the counting rates of γ-cameras in the presence of the 18F cylinder were measured with different detector orientations, distances, and energy windows. Results: The dose rate of a point or an extended source in air was proportional to the inverse square of the distance from the source. At 2 m, the dose rate for a 370-MBq 18F source was less than 20 μGy in any single hour, which is the limit for unrestricted areas. The dose rate with 0.318-cm-thick lead shielding decreased to about 60%, and that with 5.08-cm-thick lead shielding decreased to about 4%; these rates were higher than those estimated using the narrow-beam attenuation formula. The scattered photons and characteristic x-rays from the lead brick and surrounding structures may have contributed to this result. The decrease in dose rate resulting from a 33% increase in distance was similar to the effect from shielding the source with 0.318-cm-thick lead. At 3 m from a 185-MBq 18F source, the counting rate in the 99mTc window of an Orbiter camera was about 120,000/min when the detector faced the source. This rate was comparable to that of a typical 99mTc clinical study (∼200,000/min). Only when the distance was increased to 11 m and the detector did not face the source did the counting rate decrease to the background level (3,234/min). The counting rate also depended on the energy window of the γ-camera. On a Vertex camera, the counting rate of 18F in the 99mTc window versus that in the 201Tl (or 67Ga) window was 1:1.7 (or 1:2.7). Conclusion: 18F dose rate can be significantly reduced with distance. Lead shielding is not as effective as was predicted. 18F sources should be kept substantial distances away from γ-cameras to avoid contamination of image quality.

Original languageEnglish (US)
Pages (from-to)210-215
Number of pages6
JournalJournal of Nuclear Medicine Technology
Volume31
Issue number4
StatePublished - Dec 1 2003

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Keywords

  • Counting rate
  • Dose rate
  • F
  • Lead shielding
  • γ-camera

ASJC Scopus subject areas

  • Radiological and Ultrasound Technology
  • Radiology Nuclear Medicine and imaging

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