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Research and Reviews : A Journal of Medical Science and Technology

Activity Quantification of Lu-177 SPECT/CT Imaging for Calibration Factor Analysis in Clinical Radionuclide Dosimetry

  1. Madhulika Mehrotra
  2. Sanjana Ballal
  3. Prashant Mishra
  4. C S Bal

Abstract

Purpose: To evaluate the calibration factor (CF) at three-time points with the same protocol & acquisition parameters for the images of Lu-177 activity, scanned by two different SPECT/CTs (GE & MEDISO) using a cylindrical Jaszczak phantom with cold inserts, filled with uniform activity in water and to analyze the changes in the calibration factor data with time. The purpose of the study is to quantitatively analyze the first step (calibration acquisition) in clinical dosimetry workflow. Methods: The study was performed two times as SET-I and SET-II, with a gap of six months with the same phantom and SPECT/CTs for three-time points (Day 0, Day 4 & Day 7). A known activity of Lu-177 was filled in the Jaszczak phantom with uniform activity in the water solution. The scans were performed by the two dual- headed SPECT/CTs (GE & MEDISO) with high energy general purpose (HEGP) collimator. To calculate the calibration factor, the counts are evaluated from reconstructed images for the same volume of interest (VOI) to convert into the activity. Results: In the SET-I study, the CFs obtained from GE SPECT/CT showed that the CF remains approximately constant for two-time points (Day 0 & Day 7) and was less on Day 4. For MEDISO SPECT/CT, the CF remains approximately constant for two-time points (Day 4 & Day 7), but on Day 0, the CF was less. In the SET-II study, the CF obtained from GE SPECT/CT and MEDISO SPECT/CT, at three-time points shows that the CF remains approximately constant for the uniformly distributed Lu-177 activity in the phantom. Conclusion: Our study supports that uniform activity distributed over the entire phantom volume and reconstructed images obtained from the SPECT/CT with attenuation & scatter corrections are essential steps for accurately evaluating calibration factors in clinical dosimetry workflow.

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