90Y Positron Emission Tomography Research Articles

Liver Tumor Enhancement at Hybrid Angio-CT and Comparison With Tumor and Hepatic Parenchymal Distribution of Yttrium-90 Microspheres by Positron Emission Tomography.

This single-center retrospective study evaluated patients who underwent treatment of a primary or secondary hepatic malignancy with injection of glass or resin yttrium-90 (90Y) microspheres with a corresponding hybrid angiography-computed tomography (angio-CT) and 90Y positron emission tomography (PET). Volumetric contours were defined by three independent observers and were used to calculate relative tumoral enhancement at angio-CT. This parameter was compared with the tumor-to-normal (T/N) activity ratio predicted by technetium-99m macro-aggregated albumin (99mTc-MAA) single photon emission computed tomography (SPECT) and microsphere activity distribution by 90Y PET. A similar correlation was observed for the enhancement ratio at angio-CT with observed microspheredistribution at 90Y PET (r=0.34) to that predicted by 99mTc-MAA SPECT (r=0.32). The enhancement ratio on angio-CT performed as well as 99mTc-MAA in the prediction of 90Y PET activity distribution. The technique could not be readily applied to tumors with large areas of hypoattenuation (necrosis) on angio-CT.With refinement and further study, this technique could be used as a quantitative adjunct to standard-of-care99mTc-MAA SPECT for dosimetry calculations and prediction of microsphere distribution to maximize tumor response and minimize hepatotoxicity.

Impact of acquisition time on image quality and visibility of Yttrium-90 Positron Emission Tomography: A phantom study

90Y has internal pair production which enables the imaging of this isotope with positron emission tomography (PET). The acquisition time is a crucial factor which strongly influence the image quality due to very small decay branch of this isotope. Hence, the aim of this study was to evaluate the impact of acquisition time on image quality and visibility of 90Y PET. A NEMA IEC body phantom with set of fillable spheres were filled with 90Y to generate a hot lesion to background ratio of 8:1. PET image was acquired by Philips Gemini TF PET/CT scanner with acquisition time per bed varied from 15, 30, 60 and 120 minutes. Image quality was assessed by percentage hot contrast (HC), image noise (CV), signal-to-noise (SNR) ratio and visibility (VS). From a result, hot spheres and their edges were more defined as acquisition time increased. Additionally, SNR and visibility were increased with acquisition time and sphere size as expected but percentage hot contrast was decreased. Thus, this can be explained by the growing of noise at shorter acquisition times and smaller spheres. In conclusion, 90Y PET imaging was feasible but the imaging protocol should be carefully considered particularly in small object.

Comparison of the 90Y-labelled glass microspheres liver radioembolisation dosimetry with the estimated dosimetry obtained from pre-treatment 99mTc-MAA SPECT images reconstructed with and without attenuation correction

ABSTRACT90Y-labelled glass microspheres liver radioembolisation is an effective treatment for unresectable hepatic tumours. Its treatment planning is based on 99mTc-macro-aggregated albumin (MAA) single photon emission computed tomography (SPECT) imaging. However, photons interaction with human tissues may significantly compromise the accuracy of radioactivity quantification in nuclear medicine. The aim of this work is to evaluate the impact of a patient-specific attenuation correction on pre-treatment 99mTc-MAA SPECT images and, consequently, on the estimation of radioembolisation dosimetry. The methodology developed for attenuation correction was firstly validated on phantom models. Following this, a data set of eight patients was retrospectively selected from our database and the pre-treatment images were reconstructed with and without attenuation correction. Then, the liver dosimetry maps were estimated and compared with the liver dosimetry maps estimated from the post-treatment 90Y positron emission tomography images. Results show that the attenuation corrected phantom images were greatly improved, originating higher contrast, signal-to-noise ratio and contrast-to-noise ratio comparatively to non-attenuation corrected images. Attenuation corrected clinical pre-treatment images significantly increase the agreement, measured with the intraclass correlation coefficient, between predictive and post-treatment dosimetry maps comparatively to the non-attenuation corrected ones (Wilcoxon test, p = 0.008). In conclusion, a statistically significant increase in the agreement was achieved; however, poor correlation is still observed at the single-voxel level in some patients. Thus, future research should be addressed to investigate the reasons of this and manage to optimise the agreement between the predictive and post-treatment dosimetry.

Multi institutional quantitative phantom study of yttrium-90 PET in PET/MRI: the MR-QUEST study

BackgroundYttrium-90 (90Y) radioembolization involves the intra-arterial delivery of radioactive microspheres to treat hepatic malignancies. Though this therapy involves careful pre-treatment planning and imaging, little is known about the precise location of the microspheres once they are administered. Recently, there has been growing interest post-radioembolization imaging using positron-emission tomography (PET) for quantitative dosimetry and identifying lesions that may benefit from additional salvage therapy. In this study, we aim to measure the inter-center variability of 90Y PET measurements as measured on PET/MRI in preparation for a multi-institutional prospective phase I/II clinical trial.Eight institutions participated in this study and followed a standardized phantom filling and imaging protocol. The NEMA NU2-2012 body phantom was filled with 3 GBq of 90Y chloride solution. The phantom was imaged for 30 min in listmode on a Siemens Biograph mMR non-TOF PET/MRI scanner at five time points across 10 days (0.3–3.0 GBq). Raw PET data were sent to a central site for image reconstruction and data analysis. Images were reconstructed with optimal parameters determined from a previous study. Volumes of interest (VOIs) matching the known sphere diameters were drawn on the vendor-provided attenuation map and propagated to the PET images. Recovery coefficients (RCs) and coefficient of variation of the RCs (COV) were calculated from these VOIs for each sphere size and activity level.ResultsMean RCs ranged from 14.5 to 75.4%, with the lowest mean RC coming from the smallest sphere (10 mm) on the last day of imaging (0.16 MBq/ml) and the highest mean RC coming from the largest sphere (37 mm) on the first day of imaging (2.16 MBq/ml). The smaller spheres tended to exhibit higher COVs. In contrast, the larger spheres tended to exhibit lower COVs. COVs from the 37 mm sphere were < 25.3% in all scans. For scans with ≥ 0.60 MBq/ml, COVs were ≤ 25% in spheres ≥ 22 mm. However, for all other spheres sizes and activity levels, COVs were usually > 25%.ConclusionsPost-radioembolization dosimetry of lesions or other VOIs ≥ 22 mm in diameter can be consistently obtained (< 25% variability) at a multi-institutional level using PET/MRI for any clinically significant activity for 90Y radioembolization.

Correlation of Technetium-99m Macroaggregated Albumin and Yttrium-90 Glass Microsphere Biodistribution in Hepatocellular Carcinoma: A Retrospective Review of Pretreatment Single Photon Emission CT and Posttreatment Positron Emission Tomography/CT

PurposeTo evaluate whether technetium-99 (99mTc)-labeled macroaggregated albumin (MAA) can predict subsequent yttrium-90 (90Y) distribution and imaging response in patients with hepatocellular carcinoma (HCC). MaterialsRetrospective review was performed of records of 83 patients with HCC who underwent 90Y glass microsphere radioembolization with 99mTc-MAA single photon emission computed tomography (SPECT) and 90Y positron emission tomography (PET)/CT between January 2013 and December 2014. Images were fused to segment the whole liver normal tissue (WLNT) and the largest tumors. Fused images were reviewed and analyzed for comparison of absorbed dose (AD) to tumors and WLNT as calculated from 99mTc-MAA SPECT and from 90Y PET/CT, subjective imaging comparison of 99mTc-MAA SPECT and 90Y PET for tumors and WLNT, and correlation of tumoral AD with response on follow-up CT. ResultsFinal analysis included 73 and 63 patients for WLNT and tumor 99mTc-MAA/90Y correlation, respectively, and 62 patients for AD vs response. 99mTc-MAA/90Y limit of agreement for each reviewer was viewed as clinically acceptable only for WLNT (–15 to 15 Gy). AD interreviewer variability was clinically acceptable for WLNT but was too broad for tumor. Mean tumor AD for objective response (78%) was 313 Gy vs 234 Gy for nonresponders. No threshold was found between tumor AD and response (P > .1). Catheter mismatch between 99mTc-MAA and 90Y had a direct impact on AD mismatch between the 2 image sets. Conclusions99mTc-MAA was found to be a poor surrogate to quantitatively predict subsequent 90Y AD to hepatocellular tumors. 99mTc-MAA distribution correlated with 90Y distribution in the normal hepatic parenchyma.

WE‐AB‐BRA‐05: PET‐Guided Delivery Quality Evaluation of Yttrium‐90 Microsphere Radioembolizaton for Hepatocellular Carcinoma Patients: The Optimal Sequence of Radioembolizaton and Chemoembolization Treatments

Purpose:Selective‐internal‐radiation‐therapy (SIRT) and transarterial‐chemoembolization (TACE) are commonly used for treatment of liver tumors. The use of TACE, which is macroembolic, prior to SIRT may cause hemodynamic changes in tumor vasculature that impair yttrium‐90 (90Y) microsphere delivery to the targeted lesions. This work aims to quantify dosimetric tumor coverage using 90Y positron emission tomography (PET) dosimetry after SIRT alone compared to TACE followed by SIRT.Methods:A total of 40 consecutive hepatocellular carcinoma (HCC) SIRT patients who had a post‐SIRT 90Y PET/CT scan were evaluated. The patient‐specific‐3D‐dose was reconstructed from the PET images. Patients were categorized into two groups: patients received TACE prior SIRT procedure (n=18) and patient received SIRT alone (n=22). The lesions and liver were delineated by a senior radiologist. We evaluated both the lesion‐specific dose‐volume‐histogram (DVH) and the selectivity index (SI) defined as the ratio of the average dose inside the total lesion(s) and the average dose of the normal liver. The SI values of patients were compared based on whether TACE was previously used.Results:A wide spectrum was observed in the lesion‐specific DVH‐evaluation and SI appeared to be suitable of evaluating the quality of each SIRT infusion. The average SI of the entire patient group was 3.0, i.e. targeted lesion receiving three times higher dose than normal liver. The average SI was 1.8 for patients who had prior TACE and 3.9 for patients who did not have prior TACE (p=0.008). 85% of the patients with prior TACE demonstrated poor 90Y‐microsphere delivery (SI &lt;2) while none demonstrated excellent delivery (SI &gt;4). On the other hand, the incidence SI &gt;4 among patients with no prior TACE was 37%.Conclusion:3D dose evaluation using post‐SIRT PET suggests that 90Y microsphere delivery to liver tumors is impaired among patients who received prior TACE compared to those who receive SIRT alone.

Phantom study to determine optimal PET reconstruction parameters for PET/MR imaging of 90Y microspheres following radioembolization

Yttrium-90 (90Y) radioembolization involves the intra-arterial delivery of radioactive microspheres for treating liver tumors. Although primarily a β− emitter, 90Y occasionally emits positrons via internal pair production. There is growing interest in positron emission tomography (PET) imaging of these microspheres following radioembolization to localize and quantify their distribution. Due to the low abundance of positron emission (0.0032%), the PET images are highly sensitive to the parameters of iterative reconstruction algorithms used in clinical PET imaging. In this study, we aim to determine the optimal 90Y PET reconstruction parameters for PET/MRI that provide maximal activity recovery while maintaining a moderate noise level. We imaged an ACR phantom filled with 90Y chloride solution on two Siemens Biograph mMR scanners with a total activity of 1.00 GBq–7.43 GBq. Images were reconstructed with varying iteration number, post-reconstruction filter size, and scatter correction method. In addition, we evaluated the effects of incorporating point spread function (PSF) compensation as well as reducing the scan time and imaging off the central axis of the scanner in order to simulate realistic patient acquisition protocols as closely as possible. Recovery coefficients (RCs) for hot cylinders 8–25 mm in diameter reached near convergence with limited noise at 3 iterations, 21 subsets, 5 mm FWHM Gaussian post-reconstruction filter, use of PSF compensation, and absolute scatter correction across all scans. RCs increased by as much as 17% and noise decreased by as much as 29% when scan time duration was 30 min compared to only 15 min. Images acquired with the phantom placed 7–10 cm off the central axis of the scanner exhibited slightly reduced RCs, especially for the lowest activity scan. Although optimal reconstruction parameters with current reconstruction software were determined in this study, these parameters failed to achieve perfect count recovery, suggesting further investigation of 90Y PET imaging is required.

Intraprocedural Yttrium-90 Positron Emission Tomography/CT for Treatment Optimization of Yttrium-90 Radioembolization

Radioembolization with yttrium-90 (90Y) microspheres relies on delivery of appropriate treatment activity to ensure patient safety and optimize treatment efficacy. We report a case in which 90Y positron emission tomography (PET)/computed tomography (CT) was performed to optimize treatment planning during a same-day, three-part treatment session. This treatment consisted of (i) an initial 90Y infusion with a dosage determined using an empiric treatment planning model, (ii) quantitative 90Y PET/CT imaging, and (iii) a secondary infusion with treatment planning based on quantitative imaging data with the goal of delivering a specific total tumor absorbed dose.

Patient dosimetry for selective internal radiation treatment based on PET imaging

Until recently, the radiation dose to patients undergoing the 90Y selective internal radiation treatment (SIRT) procedure is determined by applying the partition model to 99mTc MAA pretreatment scan. There can be great uncertainty in radiation dose calculated from this approach and we presented a method to compute the 3D dose distributions resulting from 90Y SIRT based on 90Y positron emission tomography (PET) imaging. Five 90Y SIRT treatments were retrospectively analyzed. After 90Y SIRT, patients had 90Y PET/CT imaging within 6 hours of the procedure. To obtain the 3D dose distribution of the patients, their respective 90Y PET images were convolved with a Monte Carlo generated voxel dose kernel. The sensitivity of the PET/CT scanner for 90Y was determined through phantom studies. The 3D dose distributions were then presented in DICOM RT dose format. By applying the linear quadratic model to the dose data, we derived the biologically effective dose and dose equivalent to 2 Gy/fraction delivery, taking into account the spatial and temporal dose rate variations specific for SIRT. Based on this data, we intend to infer tumor control probability and risk of radiation induced liver injury from SIRT by comparison with established dose limits. For the five cases, the mean dose to target ranged from 51.7 ± 28.6Gy to 163 ± 53.7 Gy. Due to the inhomogeneous nature of the dose distribution, the GTVs were not covered adequately, leading to very low values of tumor control probability. The mean dose to the normal liver ranged from 21.4 ± 30.7 to 36.7 ± 25.9 Gy. According to QUANTEC recommendation, a patient with primary liver cancer and a patient with metastatic liver cancer has more than 5% risk of radiotherapy‐induced liver disease (RILD).PACS number: 87.53.Bn