Abstract
90Y PET/CT following radioembolization has recently been established as a viable diagnostic tool, capable of producing images that are both quantitative and have superior image quality than alternative 90Y imaging modalities. Because radioembolization is assumed to be a permanent implant, it is possible to convert quantitative 90Y PET image sets into data representative of spatial committed absorbed-dose. Multiple authors have performed this transformation using dose-point kernel (DPK) convolution to account for the transport of the high-energy 90Y β-particles. This article explores a technique called the Local Deposition Method (LDM), an alternative to DPK convolution for 90Y image-based dosimetry. The LDM assumes that the kinetic energy from each 90Y β-particle is deposited locally, within the voxel where the decay occurred. Using the combined analysis of phantoms scanned using 90Y PET/CT and ideal mathematical phantoms, an accuracy comparison of DPK convolution and the LDM has been performed. Based on the presented analysis, DPK convolution provides no detectible accuracy benefit over the LDM for 90Y PET-based dosimetry. For PET systems with 90Y resolution poorer than 3.25 mm at full-width and half-max using a small voxel size, the LDM may produce a dosimetric solution that is more accurate than DPK convolution under ideal conditions; however, image noise can obscure some of the perceived benefit. As voxel size increases and resolution decreases, differences between the LDM and DPK convolution are reduced. The LDM method of post-radioembolization dosimetry has the advantage of not requiring additional post-processing. The provided conversion factors can be used to determine committed absorbed-dose using conventional PET image analysis tools. The LDM is a recommended option for routine post-radioembolization 90Y dosimetry based on PET/CT imaging.
Highlights
The complexity of techniques for 90Y radioembolization treatment-planning and post-infusion dosimetry has grown significantly in recent years
Dimensional (3-D) absorbed-dose maps, which can be utilized for analysis of dose-volume histograms (DVH) and comparison of tumor-absorbed-dose with known tumoricidal thresholds. 90Y PET/CT has recently been shown to be an alternative to traditional post-infusion 90Y imaging methods. 90Y PET provides superior image quality to alternative modalities, but imaging is quantifiable to a high degree of accuracy [3]
A comparison of the Integrated dose-volume histograms (IDVH) for the Local Deposition Method (LDM) and DPK using data from reconstruction 1 (Table 1) with 4 mm3 isotropic voxels is presented in Figures 3 and 4 for the 17 and 37 mm hot-spheres, respectively
Summary
The complexity of techniques for 90Y radioembolization treatment-planning and post-infusion dosimetry has grown significantly in recent years. Imagebased dosimetry for radioembolization has been performed and results reported in the literature both with and without the use of 90Y PET/CT using dose-point-kernel (DPK) convolution. Numerous authors have used DPK convolution as a tool to compute absorbed-dose in both patient and phantom studies using post-infusion imaging with 90Y PET/CT [6,7,8,9,10,11]. Many Monte Carlo codes have been employed in the 90Y PET literature for this purpose including EGSnrc [4], MCNP-X [10], and FLUKA [9]. These techniques are further detailed in a review of 90Y
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