Evaluation of yttrium-90 positron emission tomography dosimetry

<p><strong>Purpose:</strong> Radioembolization is a novel treatment which utilizes the liver's unique dual system blood supply to trap yttrium-90 (⁹⁰Y) microspheres in microvasculature near liver tumors. Radioembolization dose planning and dosimetry are based on crude, inaccurate assumptions due to the lack of knowledge of patient specific ⁹⁰Y microsphere distribution. In recent years, the very small 3.1867e-5 internal pair production decay branch of ⁹⁰Y has been shown to allow for positron emission tomography (PET) imaging following radioembolization. This work explores the accuracy and limitation of ⁹⁰Y PET imaging due to the extremely low signal to noise (SNR) ratio associated with ⁹⁰Y and verifies the accuracy of using these PET images for 3-dimensional (3D) dosimetry. ^ <strong>Material and Methods:</strong> PET acquisitions of a phantom containing ⁹⁰Y filled cylindrical inserts were acquired to determine quantitative accuracy of the PET images to measure ⁹⁰Y activity. Numerous reconstruction algorithms were used to determine the optimal protocol to balance image noise and accuracy. A GATE model of the PET scanner was used to evaluate the origin of prompt signal and random noise coincidence counts in these PET acquisitions. PET images were converted to dose maps using standard S-kernel convolution. Polymer gel dosimetry was used to validate the 3D dose map results. Furthermore, PET, with associated CT images, were used as input data into MC simulations to model dose rates surrounding patients for future patient release studies. A Siemens^® Biograph 64 TruePoint PET/CT was used for all acquisitions and reconstructions. ^<strong>Results:</strong> The phantom study determined Siemens® OSEM-PSF algorithm, known as TrueX, with 2 iterations and 14 subsets had the optimal balance of noise and accuracy. Using this reconstruction algorithm, the PET images were found to accurately measure activity and calculated dose within 10% when ⁹⁰Y concentration was above the minimum detectable concentrations (MDC) of 1 MBq/ml. However, this reconstruction algorithm was shown to have a positive bias in areas where concentration was below the MDC due to truncation of negative sinogram bin values caused by statistical noise in the random correction. Polymer gel dosimetry verified the accuracy of PET dose maps but also identified a limitation in cases of highly gradient distributions due to the PET spatial resolution spreading of measured activity. Additionally, external dose rates were found to be accurately predicted through use of ⁹⁰Y PET/CT images as inputs into a MC simulation.<strong>Conclusion:</strong> Research in ⁹⁰Y PET/CT has quickly been expanding over recent years as a feasible method to provide liver distribution of ⁹⁰Y following radioembolization. This study demonstrates the accuracy and limitations of the use of these ⁹⁰Y PET/CT images in patient specific qualitative dosimetry.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Health and Kinesiology

Year

2014

Author dc:creator

• Tapp, Katherine N

Contributors dc:contributor

• Gary Hutchins
• Keith Stantz
• Ulrike Dydak
• Shuang Liu

• Medical Imaging
• Medicine and Health Sciences
• Physics

Repository record dc:identifier

https://docs.lib.purdue.edu/open_access_dissertations/374

OAI identifier oai:identifier

oai:docs.lib.purdue.edu:open_access_dissertations-1535