Reed Selwyn

18F-labeled resin microspheres as surrogates for 90Y resin microspheres used in the treatment of hepatic tumors: a radiolabeling and PET validation study

(90)Y-labeled resin microspheres (SIR-Spheres) are currently used to treat patients with primary and metastatic solid liver tumors. This treatment is typically palliative since patients have exhausted all other standard treatment options. Improving the quality of life and extending patient survival are typical benchmarks for tracking patient response. However, the current method for predicting microsphere biodistributions with (99m)Tc-labeled macroaggregated albumin (MAA) does not correlate well with patient response. This work presents the development of a new (18)F-labeled resin microsphere to serve as a surrogate for the treatment microsphere and to employ the superior resolution and sensitivity of positron emission tomography (PET). The (18)F microsphere biodistributions were determined in a rabbit using PET imaging and histological review. The PET-based uptake ratio was shown to agree with the histological findings to better than 3%. In addition, the radiolabeling process was shown to be rapid, efficient and relatively stable in vivo.

86Y and 89Zr as PET Imaging Surrogates for 90Y: A Comparative Study

A comparative study of radioactive properties, production and microPET imaging performance issues between 86Y and 89Zr is made.

Technical note : The calibration of 90Y-labeled SIR-Spheres® using a nondestructive spectroscopic assay

90Y-labeled SIR-Spheres are currently used to treat patients with hepatic metastases secondary to colorectal adenocarcinoma. In general, the prescribed activity is based on empirical data collected during clinical trials. The activity of the source vial is labeled by the manufacturer as 3.0 GBq +/- 10% and is not independently verified by the end user. This technical note shows that the results of a nondestructive spectroscopic assay of a SIR-Spheres sample was 26% higher than the activity stated by the manufacturer. This difference should not impact the current empirical prescription method but may be problematic for patient-specific dosimetry applications, such as image-based dosimetry.

Phantoms for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) provides exceptional soft tissue contrast and is capable of generating quantitative maps to demonstrate blood flow, water diffusion, temperature distribution, and tissue relaxation properties. MRI also has widely known drawbacks such as high cost and long acquisition times

SU‐GG‐AUD‐03: The Development and Validation of An Image‐Based Dosimetry System for 90Y Microspheres Used to Treat Hepatic Tumors

Purpose: To develop and experimentally validate an image‐baseddosimetry system for determining the three‐dimensional (3D) dose distribution from 90 Y microspheres used to treat hepatic tumors.Method and Materials: A rapid, efficient, and stable batch technique was used to label yttrium‐loaded microspheres with 18 F . These 18 F ‐labeled microspheres served as surrogates for 90 Y ‐labeled microspheres. 18 F and 90 Y microspheres were coinjected into a gel‐based phantom and the 18 F activity distribution was determined using a GE Discovery LS PET/CT scanner. The activity distribution was converted from 18 F to 90 Y by applying a precise activity ratio, which was determined using germanium detection and a low uncertainty 90 Y positron branching ratio. To calculate the dose, the image data was convolved with a 90 Y dose point kernel using 3D‐ID software. This dose was compared to the dose measured in the central plane using HD‐810 radiochromic film and a new film protocol. The film protocol and the gel‐based phantom were validated using a single 90 Sr / 90 Y source seed. The film was calibrated using two NIST‐traceable 90 Sr ophthalmic applicators and was analyzed using a flatbed scanner in reflective mode. Additionally, the image‐based dose to the entire gel phantom was compared to a Monte Carlo‐derived dose. Results: The image‐based (3D‐ID) dose in the central plane was 90.20 Gy ± 6% and the film measured dose was 90.64 Gy ± 5%. A mean phantom dose of 74.30 Gy ± 6% and 74.70 Gy ± 2% was determined using 3D‐ID and Monte Carlo, respectively. Overall, these results agreed to within 0.5%. The image‐basedin vivo dose volume histogram (DVH) for this study was in excellent agreement with the film measured DVH. Conclusion: Through the implementation of 18 F ‐labeled microspheres, a precise non‐destructive assay of 90 Y , and a validated film protocol, a new image‐baseddosimetry system for 90 Y microspheres was experimentally validated.