Abstract
This work demonstrates the efficacy of voxel‐based 90Y microsphere dosimetry utilizing post‐therapy SPECT/CT imaging and applies it to the prediction of treatment response for the management of patients with hepatocellular carcinoma (HCC). A 90Y microsphere dosimetry navigator (RapidSphere) within a commercial platform (Velocity, Varian Medical Systems) was demonstrated for three microsphere cases that were imaged using optimized bremsstrahlung SPECT/CT. For each case, the 90Y SPECT/CT was registered to follow‐up diagnostic MR/CT using deformable image registration. The voxel‐based dose distribution was computed using the local deposition method with known injected activity. The system allowed the visualization of the isodose distributions on any of the registered image datasets and the calculation of dose‐volume histograms (DVHs). The dosimetric analysis illustrated high local doses that are characteristic of blood‐flow directed brachytherapy. In the first case, the HCC mass demonstrated a complete response to treatment indicated by a necrotic region in follow‐up MR imaging. This result was dosimetrically predicted since the gross tumor volume (GTV) was well covered by the prescription isodose volume (V150 Gy = 85%). The second case illustrated a partial response to treatment which was characterized by incomplete necrosis of an HCC mass and a remaining area of solid enhancement in follow‐up MR imaging. This result was predicted by dosimetric analysis because the GTV demonstrated incomplete coverage by the prescription isodose volume (V470 Gy = 18%). The third case demonstrated extrahepatic activity. The dosimetry indicated that the prescription (125 Gy) isodose region extended outside of the liver into the duodenum (178 Gy maximum dose). This was predictive of toxicity as the patient later developed a duodenal ulcer. The ability to predict outcomes and complications using deformable image registration, calculated isodose distributions, and DVHs, points to the clinical utility of patient‐specific dose calculations for 90Y radioembolization treatment planning.
Highlights
Radionuclide therapy using Yttrium‐90 (90Y) microspheres has emerged as an effective treatment modality for the management of patients with primary and metastatic hepatocellular carcinoma (HCC).[1]
We demonstrate how commercial voxel‐based absorbed dose calculation software applied to post‐therapy 90Y bremsstrahlung single photon emission computed tomography (SPECT) imaging can facilitate dosimetric verification during the course of 90Y therapy
All patients underwent imaging and clinical evaluation before treatment. This included arterial mapping and abdominal Technetium‐99m‐macroaggregated albumin (99mTc‐ MAA) SPECT/computed tomography (CT) to assess the potential for extrahepatic uptake and determine the feasibility, safety, and number of injections required for treatment
Summary
Radionuclide therapy using Yttrium‐90 (90Y) microspheres has emerged as an effective treatment modality for the management of patients with primary and metastatic hepatocellular carcinoma (HCC).[1]. Current practice uses manufacturer‐recommended prescription activity and dose calculations, derived from the Medical Internal Radiation Dose (MIRD) Committee of the Society of Nuclear Medicine, which are based on the size of the intended treatment volume.[5] Despite positive results from published studies,[6,7] the reported doses assume that the activity distribution within the treatment volume is uniform. Quantitative patient‐specific 90Y dosimetry has been studied using bremsstrahlung single photon emission computed tomography (SPECT)/computed tomography (CT) 8–11 and positron emission tomography (PET)/CT.[12,13,14,15,16] such dosimetric studies have utilized research software that is not readily available to the medical community and have not illustrated scenarios where voxel‐based dosimetry could be used to predict treatment response
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