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A Novel Method for Dosimetry Calculation Utilizing PET-CT in Patients Treated with Radioembolization

E Fourkal

E Fourkal*, I Veltchev, M Lin, M Johnson, C Ma, M Doss, J Yu, J Meyer, Fox Chase Cancer Center, Philadelphia, PA

WE-G-500-7 Wednesday 4:30PM - 6:00PM Room: 500 Ballroom

Radioembolization is an emerging therapeutic option for the treatment of metastatic and primary tumors of the liver. Simple formulas are currently utilized in order to prescribe the appropriate activity. While the activity infused to each patient is known, limited data is available concerning the delivered dose. This makes correlation of response to dose impossible. The aim of this study is to establish a method for calculation of dose delivered to intrahepatic targets.

Six patients were enrolled in this study as part of one approved clinical trial. All patients underwent radioembolization for primary or metastatic liver tumor(s). Each patient underwent a post-treatment PET-CT for the quantification of activity of Yttrium-90 labeled microspheres. The absorbed dose is calculated as the convolution of the pre-calculated dose kernel with the PET-measured activity.

Four patients underwent treatment with SIR-Spheres for liver metastases from colorectal cancer and 2 patients were treated with Therasphere for hepatocellular cancer. A total of 11 target tumors were contoured on post-treatment PET-CT scans for dosimetric evaluation. Mean prescription activity was 1.51 GBq (range: 0.58 to 3.29 GBq). The resulting mean maximum measured dose to targets was 167 Gy (range: 71 to 311 Gy). Mean minimum dose to 70% of target (D70) was 54 Gy (range: 29 to 83 Gy). Mean minimum dose to 90% of target (D90) was 36 Gy (range: 13 to 58 Gy). The mean maximum dose for Therasphere and SIR-spheres was 266 Gy versus 111 Gy.

This pilot project demonstrates that dose can be calculated in patients after radioembolization, utilizing PET-CT measured activity. Although this represents preliminary work with a small number of patients, the doses to patients treated with Therasphere may be larger. This process could lay the foundation for more sophisticated dose prescription methods in the future.

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