Factors affecting accuracy of S values and determination of time-integrated activity in clinical Lu-177 dosimetry

Ann Nucl Med. 2019 Jul;33(7):521-531. doi: 10.1007/s12149-019-01365-6. Epub 2019 May 22.

Abstract

Introduction: In any radiotherapy, the absorbed dose needs to be estimated based on two factors, the time-integrated activity of the administered radiopharmaceutical and the patient-specific dose kernel. In this study, we consider the uncertainty with which such absorbed dose estimation can be achieved in a clinical environment.

Methods: To calculate the total error of dose estimation we considered the following aspects: The error resulting from computing the time-integrated activity, the difference between the S-value and the patient specific full Monte Carlo simulation, the error from segmenting the volume-of-interest (kidney) and the intrinsic error of the activimeter.

Results: The total relative error in dose estimation can amount to 25.0% and is composed of the error of the time-integrated activity 17.1%, the error of the S-value 16.7%, the segmentation error 5.4% and the activimeter accuracy 5.0%.

Conclusion: Errors from estimating the time-integrated activity and approximations applied to dose kernel computations contribute about equally and represent the dominant contributions far exceeding the contributions from VOI segmentation and activimeter accuracy.

Keywords: Lu-177 dosimetry; Monte Carlo simulations; S-values; SPECT/CT; Time integrated activity.

MeSH terms

  • Humans
  • Lutetium / therapeutic use*
  • Monte Carlo Method
  • Phantoms, Imaging
  • Precision Medicine
  • Radioisotopes / therapeutic use*
  • Radiometry*
  • Radiotherapy Dosage
  • Time Factors
  • Tomography, Emission-Computed, Single-Photon

Substances

  • Radioisotopes
  • Lutetium
  • Lutetium-177