PET imaging with yttrium-86: comparison of phantom measurements acquired with different PET scanners before and after applying background subtraction

Abstract

Quantitative imaging with the positron emitter (86)Y is the method of choice to determine the uptake and dosimetry of (90)Y-labelled radiopharmaceuticals. To examine the quantitative accuracy of positron emission tomography findings with (86)Y, this non-pure positron emitter was evaluated in a cylindrical phantom with rods of Teflon, water and air and measured with three different scanners: ECAT EXACT (2D/3D), ECAT HR+ (2D/3D) and PC4096+ (2D). After standard reconstruction, (86)Y radioactivity measured with the ECAT EXACT and related to the true radioactivity varied between 0.84 and 0.99 in 2D and between 0.93 and 1.20 in 3D from the first to the last acquisition (eight half-life times later). The water and Teflon rods exhibited considerable amounts of reconstructed radioactivity-21% in 2D and 67% in 3D for water and 65% and 147%, respectively, for Teflon-compared with the actual (86)Y radioactivity of the phantom. For the ECAT HR+ similar results were obtained in 3D, but there were even greater overestimations in 2D. Measurements with the PC4096+ showed rather small errors, with 10% for water and 20% for Teflon. To correct for the background of gamma-coincidences, sinograms were analysed and an experimental percentage of the background was subtracted from the sinograms. In order to minimise the errors in reconstructed radioactivity, the subtraction value had to be different for the individual scanners and modes. Our results demonstrate that (90)Y/(86)Y-based dosimetry for bone and red marrow must be regarded with caution if it is derived from regions of interest over the bone, the density of which is similar to that of Teflon. To obtain more reliable estimates, an appropriate background correction must be applied and tailored individually with respect to the scanner and acquisition mode.

VEGF in nuclear medicine: Clinical application in cancer and future perspectives (Review)

“…In a study comparing the risks of radiation-induced cancer from mammography, molecular breast imaging, and positron emitting mammography, the cumulative cancer incidence is 15-30 times higher for positron emission mammography and molecular breast imaging than for mammography (113). The estimated radiation burden of 89Zr-bevacizumab-PET is 19 mSv per tracer injection, on the basis of extrapolation from 111 In-bevacizumab data and a dosimetry study on 89Zr-U36, compared with 5.3 mSv for 18 F-FDG PET (114)(115)(116)(117). Besides bevacizumab, other radiolabeled anti-VEGF antibodies such as I-labeled VG76e (118) and HuMV833 (119) have been reported.…”

“…However, 86Y possesses its own set of challenges, in particular, its high positron energy (Emax 1⁄4 3.1 MeV) and emission of 1.08 MeV (83% abundance), which can significantly affect the image quality and recovery coefficients due to spurious coincidences. When appropriate corrections are performed, the image quality is greatly improved and is quantifiable (110,111).…”

“…Studies with radiolabeled bevacizumab for imaging tumor angiogenesis were performed in preclinical models proposing that its accumulation in the tumor was due to interactions with the VEGF-A-165 and -189 isoforms, associated with the tumor cell surface and/or the extracellular matrix (101,102). However, in a clinical study with 111 In-bevacizumab in patients affected by colorectal cancer liver metastases, there was a lack of correlation between radiolabeled bevacizumab uptake and VEGF-A expression in the lesions (103). Authors speculated that the accumulation of the mAb was due to enhanced vascular permeability leading to unspecific uptake in the tumor.…”

“…Because of better and more accurate scatter and attenuation corrections associated with PET, 86Y-labeled bevacizumab was developed for imaging VEGF-A tumor angiogenesis and as a surrogate marker for 90Y-based RIT. The 111 In and 89zr-labeled probes have been proposed as surrogate imaging markers for 90Y therapy, however, deviations were observed due to subtle differences in the metalchelate complexes and metabolism (102,109) highlighting the need for the development of isotopically matched 86Y-labeled probes for 90Y. However, 86Y possesses its own set of challenges, in particular, its high positron energy (Emax 1⁄4 3.1 MeV) and emission of 1.08 MeV (83% abundance), which can significantly affect the image quality and recovery coefficients due to spurious coincidences.…”

Irradiation of strontium chloride targets at proton energies above 35 MeV to produce PET radioisotope Y-86

“…This "nonstandard" PET radionuclide has found its application in the assessment of personalized biodistribution of 90 Y labeled radiopharmaceuticals prior to their administration [1][2][3][4][5][6][7][8]. The absence of γ -rays makes high resolution imaging of 90 Y impossible, therefore biodistribution and dosimetry evaluation is done with a different radionuclide.…”