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Objective: To assess the accuracy of a scout dose of holmium-166 poly(L-lactic acid) microspheres ((166)Ho-PLLA-MS) in predicting the distribution of a treatment dose of (166)Ho-PLLA-MS, using single photon emission tomography (SPECT).Methods: A scout dose (60 mg) was injected into the hepatic artery of five pigs and SPECT acquired. Subsequently, a 'treatment dose' was administered (540 mg) and SPECT, computed tomography (CT) and magnetic resonance imaging (MRI) of the total dose performed. The two SPECT images of each animal were compared. To validate quantitative SPECT an ex vivo liver was instilled with (166)Ho-PLLA-MS and SPECT acquired. The liver was cut into slices and planar images were acquired, which were registered to the SPECT image.Results: Qualitatively, the scout dose and total dose images were similar, except in one animal because of catheter displacement. Quantitative analysis, feasible in two animals, tended to confirm this similarity (r(2) = 0.34); in the other animal the relation was significantly better (r(2) = 0.66). The relation between the SPECT and planar images acquired from the ex vivo liver was strong (r(2) = 0.90).Conclusion: In the porcine model a scout dose of (166)Ho-PLLA-MS can accurately predict the biodistribution of a treatment dose. Quantitative (166)Ho SPECT was validated for clinical application. [ABSTRACT FROM AUTHOR]

Radioembolization with yttrium-90 microspheres ((90)Y-RE), either glass- or resin-based, is increasingly applied in patients with unresectable liver malignancies. Clinical results are promising but overall response and survival are not yet known. Therefore a meta-analysis on tumor response and survival in patients who underwent (90)Y-RE was conducted. Based on an extensive literature search, six groups were formed. Determinants were cancer type, microsphere type, chemotherapy protocol used, and stage (deployment in first-line or as salvage therapy). For colorectal liver metastases (mCRC), in a salvage setting, response was 79% for (90)Y-RE combined with 5-fluorouracil/leucovorin (5-FU/LV), and 79% when combined with 5-FU/LV/oxaliplatin or 5-FU/LV/irinotecan, and in a first-line setting 91% and 91%, respectively. For hepatocellular carcinoma (HCC), response was 89% for resin microspheres and 78% for glass microspheres. No statistical method is available to assess median survival based on data presented in the literature. In mCRC, (90)Y-RE delivers high response rates, especially if used neoadjuvant to chemotherapy. In HCC, (90)Y-RE with resin microspheres is significantly more effective than (90)Y-RE with glass microspheres. The impact on survival will become known only when the results of phase III studies are published. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the potential of magnetic resonance imaging (MRI) for accurate assessment of the three-dimensional (166)Ho activity distribution to estimate radiation-absorbed dose distributions in (166)Ho-loaded poly (L-lactic acid) microsphere ((166)Ho-PLLA-MS) liver radioembolization. Methods and Materials: MRI, computed tomography (CT), and single photon emission CT (SPECT) experiments were conducted on an anthropomorphic gel phantom with tumor-simulating gel samples and on an excised human tumor-bearing liver, both containing known amounts of (166)Ho-PLLA-MS. Three-dimensional radiation-absorbed dose distributions were estimated at the voxel level by convolving the (166)Ho activity distribution, derived from quantitative MRI data, with a (166)Ho dose point-kernel generated by MCNP (Monte Carlo N-Particle transport code) and from Medical Internal Radiation Dose Pamphlet 17. MRI-based radiation-absorbed dose distributions were qualitatively compared with CT and autoradiography images and quantitatively compared with SPECT-based dose distributions. Both MRI- and SPECT-based activity estimations were validated against dose calibrator measurements. Results: Evaluation on an anthropomorphic phantom showed that MRI enables accurate assessment of local (166)Ho-PLLA-MS mass and activity distributions, as supported by a regression coefficient of 1.05 and a correlation coefficient of 0.99, relating local MRI-based mass and activity calculations to reference values obtained with a dose calibrator. Estimated MRI-based radiation-absorbed dose distributions of (166)Ho-PLLA-MS in an ex vivo human liver visually showed high correspondence to SPECT-based radiation-absorbed dose distributions. Quantitative analysis revealed that the differences in local and total amounts of (166)Ho-PLLA-MS estimated by MRI, SPECT, and the dose calibrator were within 10%. Excellent agreement was observed between MRI- and SPECT-based dose-volume histograms. Conclusions: Quantitative MRI was demonstrated to provide accurate three-dimensional (166)Ho-PLLA-MS activity distributions, enabling localized intrahepatic radiation-absorbed dose estimation by convolution with a (166)Ho dose point-kernel for liver radioembolization treatment optimization and evaluation. [ABSTRACT FROM AUTHOR]