Magnetic resonance imaging-based radiation-absorbed dose estimation of 166Ho microspheres in liver radioembolization.
OBJECTIVE
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
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.
Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands. p.seevinck@umcutrecht.nl
Peter R
PR
Seevinck
Gerrit H
GH
van de Maat
Tim C
TC
de Wit
Maarten A D
MA
Vente
Johannes F W
JF
Nijsen
Chris J G
CJ
Bakker
D000465:Algorithms; D001345:Autoradiography / Q000379:methods; D004621:Embolization, Therapeutic / Q000379:methods*; D006695:Holmium / Q000493:pharmacokinetics*; D006801:Humans; D019344:Lactic Acid / Q000493:pharmacokinetics*; D008099:Liver / Q000000981:diagnostic imaging / Q000378:metabolism; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008863:Microspheres; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011091:Polyesters; D011108:Polymers / Q000493:pharmacokinetics*; D011868:Radioisotopes / Q000493:pharmacokinetics*; D011879:Radiotherapy Dosage; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods; D014057:Tomography, X-Ray Computed
D011091:Polyesters; D011108:Polymers; D011868:Radioisotopes; D019344:Lactic Acid; C033616:poly(lactide); D006695:Holmium