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Employing Bioerodible Eluting-Spacers for Radiotherapy Applications with In Situ Dose Painting

F Boateng1*, W Ngwa2,3, (1) Versant Medical Physics & Radiation Safety,Kalamazoo, MI, (2) Harvard Medical School, Boston, MA, (3) University of Massachusetts, Lowell, MA


(Tuesday, 7/31/2018) 4:30 PM - 6:00 PM

Room: Davidson Ballroom A

Purpose: To investigate the feasibility of using bioerodible polymeric spacer over biodegradable spacers loaded with gold nanoparticles (AuNP) for radiotherapy applications with in situ dose painting, and to explore dosimetric impact on dose enhancement ratio of different radioisotopes.

Methods: Mathematical models were proposed based on experimentally reported erosion rate constant (k0 = 5.5E-7 kgm^-2s^-1) for bioerodible matrix. An in vivo determined diffusion coefficient (2.2E-8 cm^2/s) of 10-nm AuNP of concentration 7 mg/g was used to estimate diffusion coefficient of other AuNP sizes (2, 5, 14-nm) using the Stoke-Einstein diffusion equation. The corresponding dose enhancement factors were considered to study the dosimetric feasibility of employing bioerodible AuNP-eluting spacers for radiotherapy applications.

Results: The results indicated that preloaded AuNP could be released in hours (116 hours) after implantation compared to over a month for biodegradable spacers reported previously. This agrees with the experimental results reported for drug release from erodible matrices in hours. The proposed models agree with reported Hopfenberg equation for a cylindrical matrix undergoing surface erosion. Dose enhancement factor at tumor distance 5 mm for Cs-131 (DEF >2.2) greater than that of I-125 (DEF >2) and Pd-103 (DEF ≥2) could be achieved for AuNP sizes (2, 5, 10, and 14 nm) respectively.

Conclusion: The results highlighted a higher preload release rate that could be achieved within a short period (in hours/days) instead of month(s) in comparison to biodegradable spacers. Our findings suggest that AuNP-eluting erodible spacers could be used for short-lived radioisotopes like Pd-103 and Cs-131 compared to biodegradable eluting spacers more feasible for only long-lived radioisotopes like I-125. The erodible spacers could be designed to release preload (drug/nanoparticles) from hours to days, weeks or months for specific applications in radiotherapy, to replace the conventional inert spacers or fiducials. The models would enhance experimental work and drug delivery in situ.


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