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. 2002 Aug;43(8):1101-9.

A 3-dimensional absorbed dose calculation method based on quantitative SPECT for radionuclide therapy: evaluation for (131)I using monte carlo simulation

Michael Ljungberg  1 , Katarina Sjögreen, Xiaowei Liu, Eric Frey, Yuni Dewaraja, Sven-Erik Strand
Affiliations

A 3-dimensional absorbed dose calculation method based on quantitative SPECT for radionuclide therapy: evaluation for (131)I using monte carlo simulation

Michael Ljungberg et al. J Nucl Med. 2002 Aug.

Abstract

A general method is presented for patient-specific 3-dimensional absorbed dose calculations based on quantitative SPECT activity measurements.

Methods: The computational scheme includes a method for registration of the CT image to the SPECT image and position-dependent compensation for attenuation, scatter, and collimator detector response performed as part of an iterative reconstruction method. A method for conversion of the measured activity distribution to a 3-dimensional absorbed dose distribution, based on the EGS4 (electron-gamma shower, version 4) Monte Carlo code, is also included. The accuracy of the activity quantification and the absorbed dose calculation is evaluated on the basis of realistic Monte Carlo-simulated SPECT data, using the SIMIND (simulation of imaging nuclear detectors) program and a voxel-based computer phantom. CT images are obtained from the computer phantom, and realistic patient movements are added relative to the SPECT image. The SPECT-based activity concentration and absorbed dose distributions are compared with the true ones.

Results: Correction could be made for object scatter, photon attenuation, and scatter penetration in the collimator. However, inaccuracies were imposed by the limited spatial resolution of the SPECT system, for which the collimator response correction did not fully compensate.

Conclusion: The presented method includes compensation for most parameters degrading the quantitative image information. The compensation methods are based on physical models and therefore are generally applicable to other radionuclides. The proposed evaluation methodology may be used as a basis for future intercomparison of different methods.

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Figures

FIGURE 1
FIGURE 1
(A) Planar projection of defined activity distribution. (B) Monte Carlo simulated projection image of 131I of same activity distribution in air, that is, including only deterioration caused by collimator response and septal penetration. (C) Projection image obtained when including attenuation and scatter, which thus simulates real patient situation. (D) Projection image obtained for 32- to 132-keV scatter energy window, used for image registration procedure.
FIGURE 2
FIGURE 2
Mass density images used to mimic CT-derived mass density map for quantification. Maps 1–3 show transversal, coronal, and sagittal slices for the 3 test cases, before and after registration to SPECT image.
FIGURE 3
FIGURE 3
Flow chart describing methodology of quantification procedure and evaluation. Known activity map and gold standard absorbed dose distribution are compared with corresponding maps obtained from quantitative SPECT calculation scheme.
FIGURE 4
FIGURE 4
Transversal section of absorbed dose distribution for slice through lungs (top row) and liver (bottom row) for different cases. Images were all normalized to same gray level.
See this image and copyright information in PMC

References

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