Quantification and Absorbed Dose Estimation of I-124 using microPET
(2007)Medical Physics Programme
- Abstract (Swedish)
- Small-animal positron emission tomography (PET) has proven to be a promising and useful modality for preclinical pharmacokinetic studies. Thanks to high sensitivity and spatial resolution in the range of a few millimetres, the possibility to perform reliable and accurate quantification and absorbed dose estimates is within reach. In preclinical radioimmunotherapy (RIT), the slow targeting and clearance kinetics of the tumour targeting antibodies used as radionuclide carriers call for a PET tracer enabling imaging over a period of several days. In this respect, with a half-life of 4.2 days, 124-I is more or less an ideal tracer for such studies, also bringing with it well known chemical properties and labelling methods. However, due to... (More)
- Small-animal positron emission tomography (PET) has proven to be a promising and useful modality for preclinical pharmacokinetic studies. Thanks to high sensitivity and spatial resolution in the range of a few millimetres, the possibility to perform reliable and accurate quantification and absorbed dose estimates is within reach. In preclinical radioimmunotherapy (RIT), the slow targeting and clearance kinetics of the tumour targeting antibodies used as radionuclide carriers call for a PET tracer enabling imaging over a period of several days. In this respect, with a half-life of 4.2 days, 124-I is more or less an ideal tracer for such studies, also bringing with it well known chemical properties and labelling methods. However, due to complex decay properties, including emission of gammas of energy similar to that of annihilation photons, there are complications of using 124-I in PET.Purpose: The aim of this work was to acquire knowledge of how the properties of 124-I affect image quality in small-animal PET. Furthermore, the purpose was to perform an in vivo study including quantification, upon which absorbed dose estimates were to be based.Methods: To begin with, a basic comparison of image quality obtained with 124-I and the routinely used positron emitter 18F was performed. This was done using a couple of in-house fabricated phantoms, imaged using a microPET R4 scanner - the PET scanner used throughout this work. Secondly, as a step in the process of deciding how to quantify 124-I, the ability of direct quantification of 18F in vivo was studied. The quantified activity concentrations were compared to those of biodistribution studies of the imaged mice. Finally, a quantitative pharmacokinetic study of an 124-I labelled monoclonal antibody (MAb) was performed in a mouse model, data from which were used for absorbed dose estimates.Results: An appreciable reduction in spatial resolution and hot-to-cold image contrast was demonstrated in the image quality comparisons of 124-I and 18-F. The response to different activity concentrations was found to be linear for both 124-I and 18-F, but with a considerable loss of recovery with 124-I. The outcome of the direct quantification of 18-F in vivo showed variations that did not encourage quantification of 124-I solely based on PET image data. Instead, the PET data from the last time point was normalized to corresponding values from a direct assay, done immediately after the last time point PET scan. Good agreement between quantification of activity concentration in blood, based on direct assay of tail vein blood samples and normalized PET data, encouraged the use of this method. The absorbed dose estimates indicated an absorbed dose to tumours of between 3 to 4 Gy, indicating a non-negligible radiotherapeutic effect.Conclusion: This study indicates that the microPET R4 scanner is capable of reproducing changes in activity distribution of 124-I in vivo. By normalizing the relative uptake values from the PET images to a direct assay, done immediately after the last time point PET scan, quantification of activity concentration could be done under fairly straightforward conditions. This allowed absorbed dose estimates to be calculated. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/2157040
- author
- Hörling, Magnus
- supervisor
- organization
- year
- 2007
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Nukleärmedicin
- language
- English
- id
- 2157040
- date added to LUP
- 2011-09-13 14:06:53
- date last changed
- 2014-10-10 09:40:10
@misc{2157040,
abstract = {{Small-animal positron emission tomography (PET) has proven to be a promising and useful modality for preclinical pharmacokinetic studies. Thanks to high sensitivity and spatial resolution in the range of a few millimetres, the possibility to perform reliable and accurate quantification and absorbed dose estimates is within reach. In preclinical radioimmunotherapy (RIT), the slow targeting and clearance kinetics of the tumour targeting antibodies used as radionuclide carriers call for a PET tracer enabling imaging over a period of several days. In this respect, with a half-life of 4.2 days, 124-I is more or less an ideal tracer for such studies, also bringing with it well known chemical properties and labelling methods. However, due to complex decay properties, including emission of gammas of energy similar to that of annihilation photons, there are complications of using 124-I in PET.Purpose: The aim of this work was to acquire knowledge of how the properties of 124-I affect image quality in small-animal PET. Furthermore, the purpose was to perform an in vivo study including quantification, upon which absorbed dose estimates were to be based.Methods: To begin with, a basic comparison of image quality obtained with 124-I and the routinely used positron emitter 18F was performed. This was done using a couple of in-house fabricated phantoms, imaged using a microPET R4 scanner - the PET scanner used throughout this work. Secondly, as a step in the process of deciding how to quantify 124-I, the ability of direct quantification of 18F in vivo was studied. The quantified activity concentrations were compared to those of biodistribution studies of the imaged mice. Finally, a quantitative pharmacokinetic study of an 124-I labelled monoclonal antibody (MAb) was performed in a mouse model, data from which were used for absorbed dose estimates.Results: An appreciable reduction in spatial resolution and hot-to-cold image contrast was demonstrated in the image quality comparisons of 124-I and 18-F. The response to different activity concentrations was found to be linear for both 124-I and 18-F, but with a considerable loss of recovery with 124-I. The outcome of the direct quantification of 18-F in vivo showed variations that did not encourage quantification of 124-I solely based on PET image data. Instead, the PET data from the last time point was normalized to corresponding values from a direct assay, done immediately after the last time point PET scan. Good agreement between quantification of activity concentration in blood, based on direct assay of tail vein blood samples and normalized PET data, encouraged the use of this method. The absorbed dose estimates indicated an absorbed dose to tumours of between 3 to 4 Gy, indicating a non-negligible radiotherapeutic effect.Conclusion: This study indicates that the microPET R4 scanner is capable of reproducing changes in activity distribution of 124-I in vivo. By normalizing the relative uptake values from the PET images to a direct assay, done immediately after the last time point PET scan, quantification of activity concentration could be done under fairly straightforward conditions. This allowed absorbed dose estimates to be calculated.}},
author = {{Hörling, Magnus}},
language = {{eng}},
note = {{Student Paper}},
title = {{Quantification and Absorbed Dose Estimation of I-124 using microPET}},
year = {{2007}},
}