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Imaging 212Pb-TCMC-Trastuzumab for Alpha Radioimmunotherapy for Ovarian Cancer

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S Shen

S Shen1*, R Meredith1 , M Azure1 , D Yoder1 , J Torgue2 , E Banaga2 , (1) University of Alabama, Birmingham, AL, (2) AREVA Med LLC, Bethesda, MD


SU-C-201-5 (Sunday, July 12, 2015) 1:00 PM - 1:55 PM Room: 201

To support the phase I trial for toxicity, biodistribution and pharmacokinetics of intra-peritoneal (IP) 212Pb-TCMC-trastuzumab in patients with HER-2 expressing malignancy. A whole body gamma camera imaging method was developed for estimating amount of 212Pb-TCMC-trastuzumab left in the peritoneal cavity.
²¹²Pb decays to ²¹²Bi via beta emission. ²¹²Bi emits an alpha particle at an average of 6.1 MeV. The 238.6 keV gamma ray with a 43.6% yield can be exploited for imaging. Initial phantom was made of saline bags with 212Pb. Images were collected for 238.6 keV with a medium energy general purpose collimator. There are other high energy gamma emissions (e.g. 511keV, 8%; 583 keV, 31%) that penetrate the septae of the collimator and contribute scatter into 238.6 keV. An upper scatter window was used for scatter correction for these high energy gammas.
A small source containing 212Pb can be easily visualized. Scatter correction on images of a small 212Pb source resulted in a ~50% reduction in the full width at tenth maximum (FWTM), while change in full width at half maximum (FWHM) was <10%. For photopeak images, substantial scatter around phantom source extended to > 5 cm outside; scatter correction improved image contrast by removing this scatter around the sources. Patient imaging, in the 1st cohort (n=3) showed little redistribution of 212Pb-TCMC-trastuzumab out of the peritoneal cavity. Compared to the early post-treatment images, the 18-hour post-injection images illustrated the shift to more uniform anterior/posterior abdominal distribution and the loss of intensity due to radioactive decay.
Use of medium energy collimator, 15% width of 238.6 keV photopeak, and a 7.5% upper scatter window is adequate for quantification of 212Pb radioactivity inside peritoneal cavity for alpha radioimmunotherapy of ovarian cancer.

Funding Support, Disclosures, and Conflict of Interest: Research Support: AREVA Med, NIH 1UL1RR025777-01

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