PET/CT dosimetric mapping of Y-90 theraspheres biodistribution following radioembolization for hepatocellular cancer

Objectives To convert a post Y-90 PET/CT image count density map to a "dose map" in Gy. This would enable accurate determination of actual dose delivered to the tumor and surrounding liver and enable improved treatment planning.

Methods PET/CT Scans were acquired, using a Siemens Biograph 64 PET/CT scanner, after hepatic Y-90 therapy in 42 pts. Using MIRD methodology, thresholded PET/CT count data was converted on a voxel by voxel basis into radiation absorbed dose images. Dose volume histograms (DVHs) were generated for whole liver, liver lobes and liver lesions, which were segmented on contrast enhanced CT data sets using MIM software.

Results The initial results indicate targeted liver lesions received 155 +/- 111 Gy , with a mean of 104 Gy while the remaining targeted liver lobe received 78.6 +/- 22.4 Gy , ratio of lesion to surrounding parenchyma was 2.1 +/- 1.6. DVHs found mean doses to 66, 33, and 10% of the whole liver volume to be 7.5 +/- 15.8, 46.6 +/- 39.4, and 149.1 +/- 45.8 Gy.

Conclusions Although it is technically challenging to generate accurate dose maps from post Y-90 low count PET/CT scans, this is possible and provides essential information for effective and safe treatment planning.