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Measurements of Gold Nanoparticle-Mediated Proton Dose Enhancement Due to Particle-Induced X-Ray Emission and Activation Products Using Radiochromic Films and CdTe Detector

J Cho

J Cho1*, N Manohar1,2 , S Krishnan3 , S Cho1 , (1) Dept. of Radiation Physics, UT MD Anderson Cancer Center, Houston, TX, (2) Medical Physics Program, Georgia Institute of Technology, Atlanta, GA, (3) Dept. of Radiation Oncology, UT MD Anderson Cancer Center, Houston, TX


SU-E-T-231 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

There have been several reports of enhanced cell-killing and tumor regression when tumor cells and mouse tumors were loaded with gold nanoparticles (GNPs) prior to proton irradiation. While particle-induced x-ray emission (PIXE), Auger electrons, secondary electrons, free radicals, and biological effects have been suggested as potential mechanisms responsible for the observed GNP-mediated dose enhancement/radiosensitization, there is a lack of quantitative analysis regarding the contribution from each mechanism. Here, we report our experimental effort to quantify some of these effects.

5-cm-long cylindrical plastic vials were filled with 1.8 mL of either water or water mixed with cylindrical GNPs at the same gold concentration (0.3 mg Au/g) as used in previous animal studies. A piece of EBT2 radiochromic film (30-μm active-layer sandwiched between 80/175-μm outer-layers) was inserted along the long axis of each vial and used to measure dose enhancement due to PIXE from GNPs. Vials were placed at center-of-modulation (COM) and 3-cm up-/down-stream from COM and irradiated with 5 different doses (2-10 Gy) using 10-cm-SOBP 160-MeV protons. After irradiation, films were cleaned and read to determine the delivered dose. A vial containing spherical GNPs (20 mg Au/g) was also irradiated, and gamma-rays from activation products were measured using a cadmium-telluride (CdTe) detector.

Film measurements showed no significant dose enhancement beyond the experimental uncertainty (~2%). There was a detectable activation product from GNPs, but it appeared to contribute to dose enhancement minimally (<0.01%).

Considering the composition of EBT2 film, it can be inferred that gold characteristic x-rays from PIXE and their secondary electrons make insignificant contribution to dose enhancement. The current investigation also suggests negligible dose enhancement due to activation products. Thus, previously-reported GNP-mediated proton dose enhancement/radiosensitization needs to be attributed to one or more of the other mechanisms listed earlier.

Supported in part by NIH/NCI grant R01CA155446

Funding Support, Disclosures, and Conflict of Interest: This investigation was supported in part by NIH/NCI grant R01CA155446.

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