Magnetic Resonance Imaging-Based Radiation-Absorbed Dose Estimation of 166Ho Microspheres in Liver Radioembolization

• Published in: International journal of radiation oncology, biology, physics Vol. 83; no. 3; pp. e437 - e444
• Main Authors: Seevinck, Peter R., van de Maat, Gerrit H., de Wit, Tim C., Vente, Maarten A.D., Nijsen, Johannes F.W., Bakker, Chris J.G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-07-2012
• Subjects: Algorithms; Autoradiography - methods; Dosimetry; Embolization, Therapeutic - methods; Holmium - pharmacokinetics; Holmium microspheres; Humans; Lactic Acid - pharmacokinetics; Liver - diagnostic imaging; Liver - metabolism; Liver Neoplasms - diagnostic imaging; Liver Neoplasms - metabolism; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Microspheres; Monte Carlo Method; Phantoms, Imaging; Polyesters; Polymers - pharmacokinetics; Radiation-absorbed dose; Radioembolization; Radioisotopes - pharmacokinetics; Radiotherapy Dosage; Tissue Distribution; Tomography, Emission-Computed, Single-Photon - methods; Tomography, X-Ray Computed; Radiation-absorbed dose; Dosimetry; Magnetic resonance imaging; Radioembolization; Holmium microspheres
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/j.ijrobp.2011.12.085

To investigate the potential of magnetic resonance imaging (MRI) for accurate assessment of the three-dimensional 166Ho activity distribution to estimate radiation-absorbed dose distributions in 166Ho-loaded poly (L-lactic acid) microsphere (166Ho-PLLA-MS) liver radioembolization.
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 166Ho-PLLA-MS. Three-dimensional radiation-absorbed dose distributions were estimated at the voxel level by convolving the 166Ho activity distribution, derived from quantitative MRI data, with a 166Ho 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.
Evaluation on an anthropomorphic phantom showed that MRI enables accurate assessment of local 166Ho-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 166Ho-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 166Ho-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.
Quantitative MRI was demonstrated to provide accurate three-dimensional 166Ho-PLLA-MS activity distributions, enabling localized intrahepatic radiation-absorbed dose estimation by convolution with a 166Ho dose point-kernel for liver radioembolization treatment optimization and evaluation.