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Accuracy of 131I tumor quantification in radioimmunotherapy using SPECT imaging with an ultra-high-energy collimator: Monte Carlo study

Dewaraja, Y K; Ljungberg, Michael LU and Koral, K F (2000) In Journal of Nuclear Medicine 41(10). p.1760-1760
Abstract
Accuracy of 131I tumor quantification after radioimmunotherapy (RIT) was investigated for SPECT imaging with an ultra-high-energy (UHE) collimator designed for imaging 511-keV photons. METHODS: First, measurements and Monte Carlo simulations were carried out to compare the UHE collimator with a conventionally used, high-energy collimator. On the basis of this comparison, the UHE collimator was selected for this investigation, which was carried out by simulation of spherical tumors in a phantom. Reconstruction was by an expectation-maximization algorithm that included scatter and attenuation correction. Keeping the tumor activity constant, simulations were carried out to assess how volume-of-interest (VOI) counts vary with background... (More)
Accuracy of 131I tumor quantification after radioimmunotherapy (RIT) was investigated for SPECT imaging with an ultra-high-energy (UHE) collimator designed for imaging 511-keV photons. METHODS: First, measurements and Monte Carlo simulations were carried out to compare the UHE collimator with a conventionally used, high-energy collimator. On the basis of this comparison, the UHE collimator was selected for this investigation, which was carried out by simulation of spherical tumors in a phantom. Reconstruction was by an expectation-maximization algorithm that included scatter and attenuation correction. Keeping the tumor activity constant, simulations were carried out to assess how volume-of-interest (VOI) counts vary with background activity, radius of rotation (ROR), tumor location, and size. The constant calibration factor for quantification was determined from VOI counts corresponding to a 3.63-cm-radius sphere of known activity. Tight VOIs corresponding to the physical size of the spheres or tumors were used. RESULTS: Use of the UHE collimator resulted in a large reduction in 131I penetration, which is especially significant in RIT where background uptake is high. With the UHE collimator, typical patient images showed an improvement in contrast. Considering the desired geometric events, sensitivity was reduced, but only by a factor of 1.6. Simulation results for a 3.63-cm-radius tumor showed that VOI counts vary with background, location, and ROR by less than 3.2%, 3%, and 5.3%, respectively. The variation with tumor size was more significant and was a function of the background. Good quantification accuracy (<6.5% error) was achieved when tumor size was the same as the sphere size used in the calibration, irrespective of the other parameters. For smaller tumors, activities were underestimated by up to -15% for the 2.88-cm-radius sphere, -23% for the 2.29-cm-radius sphere, and -47% for the 1.68-cm-radius sphere. CONCLUSION: Reasonable accuracy can be achieved for VOI quantification of 131I using SPECT with an UHE collimator and a constant calibration factor. Difference in tumor size relative to the size of the calibration sphere had the biggest effect on accuracy, and recovery coefficients are needed to improve quantification of small tumors. (Less)
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Contribution to journal
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published
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in
Journal of Nuclear Medicine
volume
41
issue
10
pages
1760 - 1760
publisher
Society of Nuclear Medicine
external identifiers
  • pmid:11038009
  • scopus:0033623357
ISSN
0161-5505
language
English
LU publication?
yes
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eb0b2554-a3c1-4dc3-8ba9-36dd225ea45c (old id 1117529)
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http://jnm.snmjournals.org/cgi/content/abstract/41/10/1760
date added to LUP
2008-06-27 14:14:08
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2017-05-21 04:26:17
@article{eb0b2554-a3c1-4dc3-8ba9-36dd225ea45c,
  abstract     = {Accuracy of 131I tumor quantification after radioimmunotherapy (RIT) was investigated for SPECT imaging with an ultra-high-energy (UHE) collimator designed for imaging 511-keV photons. METHODS: First, measurements and Monte Carlo simulations were carried out to compare the UHE collimator with a conventionally used, high-energy collimator. On the basis of this comparison, the UHE collimator was selected for this investigation, which was carried out by simulation of spherical tumors in a phantom. Reconstruction was by an expectation-maximization algorithm that included scatter and attenuation correction. Keeping the tumor activity constant, simulations were carried out to assess how volume-of-interest (VOI) counts vary with background activity, radius of rotation (ROR), tumor location, and size. The constant calibration factor for quantification was determined from VOI counts corresponding to a 3.63-cm-radius sphere of known activity. Tight VOIs corresponding to the physical size of the spheres or tumors were used. RESULTS: Use of the UHE collimator resulted in a large reduction in 131I penetration, which is especially significant in RIT where background uptake is high. With the UHE collimator, typical patient images showed an improvement in contrast. Considering the desired geometric events, sensitivity was reduced, but only by a factor of 1.6. Simulation results for a 3.63-cm-radius tumor showed that VOI counts vary with background, location, and ROR by less than 3.2%, 3%, and 5.3%, respectively. The variation with tumor size was more significant and was a function of the background. Good quantification accuracy (&lt;6.5% error) was achieved when tumor size was the same as the sphere size used in the calibration, irrespective of the other parameters. For smaller tumors, activities were underestimated by up to -15% for the 2.88-cm-radius sphere, -23% for the 2.29-cm-radius sphere, and -47% for the 1.68-cm-radius sphere. CONCLUSION: Reasonable accuracy can be achieved for VOI quantification of 131I using SPECT with an UHE collimator and a constant calibration factor. Difference in tumor size relative to the size of the calibration sphere had the biggest effect on accuracy, and recovery coefficients are needed to improve quantification of small tumors.},
  author       = {Dewaraja, Y K and Ljungberg, Michael and Koral, K F},
  issn         = {0161-5505},
  language     = {eng},
  number       = {10},
  pages        = {1760--1760},
  publisher    = {Society of Nuclear Medicine},
  series       = {Journal of Nuclear Medicine},
  title        = {Accuracy of 131I tumor quantification in radioimmunotherapy using SPECT imaging with an ultra-high-energy collimator: Monte Carlo study},
  volume       = {41},
  year         = {2000},
}