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Determining Diffusion of Radioactive Activity Within Mice Tumor Model From a Novel Elastin-Like Polypeptide (ELP) Brachytherapy Source

H Song1*, J Milligan1, K Lafata1, G Kelly1, A Chilkoti1, J Cai2, F Yin1, (1) Duke University, Durham, NC,(2) Hong Kong Polytechnic University, China


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: elastin-like polypeptide (ELP) labeled with iodine-131 has been demonstrated to deliver curative radiation dose to xenografted tumor in mice via an injection to center of a solid tumor. The ELP conjugate is soluble below body temperature and undergoes a thermally triggered phase transition to become an insoluble coacervate at body temperature, allowing I-131 to deliver radiation dose to tumor. This work is to quantify activity distribution for the purpose of radiation dose calculation.

Methods: is labelled with the X-ray emitter I-125, instead of the beta emitter I-131, for SPECT imaging. With normalization of total injected activity, SPECT imaging would have allowed determining distribution of absolute activity all over the tumor if not for saturation in the center portion of the tumor on the preliminary SPECT images. However, SPECT imaging alone cannot resolve how much activity is included in the saturation. This work plans to grow tumor in 5 mice, followed with ELP injection. Allowing for 24 hours for ELP to stabilize in tumor, the mice will be sacrificed. The excised tumor with labelled I-125 will be placed in a 3D printed plastic holder and encased in a low-melt agarose, where it will then be imaged as a whole volume and biopsied at multiple locations. The radioactivity of the biopsy samples will be measured, and used to convert SPECT intensity to absolute activity.

Results: workflow has been developed and feasibility of this method has been assessed. The ELP solution is being prepared to inject 5 mice. The results will be ready to present at the time of the AAPM meeting.

Conclusion: SPECT image intensity correlated with measured absolute activity, dose modelling will be feasible and useful for planning ELP based brachytherapy for future studies.


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