Physical and Biological Interface Dose Effects in Tissue due to X-Ray-Induced Release of Secondary Radiation from Metallic Gold Surfaces

Abstract

Dose enhancement up to more than a factor of 100 was found in an environment of tissue-equivalent polymethylmethacrylate (PMMA) close to the surface of a thin metallic gold foil. The enhancement factors were determined for heavily filtered X rays (40 to 120 kV tube potential) under backscatter conditions, using thin-film radiation detectors with sub-micrometer resolution. The secondary electrons were found to range up to some 10 microm in tissue-equivalent material. Correspondingly, enhanced biological effects could be shown in vitro, using monolayers of C3H 10T1/2 mouse embryo fibroblasts exposed in intimate contact with the gold surface. The decay of the survival curves of cells irradiated on gold was significantly steeper than for those obtained from irradiation between PMMA disks with the same dose, also giving biological evidence for significantly enhanced doses at the gold interface. The shape of the inactivation curves resembled those for high-LET radiation, lacking a pronounced shoulder at the lower doses. Quantitatively, doses of e.g. 50 mGy (80 kV X rays) in homogeneous PMMA caused about 35% cell killing and 200 mGy about 80% when the cells were irradiated at the gold surface. From a comparison of these inactivation numbers with those found for irradiation between PMMA disks, biological dose enhancement factors for the cell system considered ranged up to about a factor of 50. In addition to cell inactivation, the in vitro irradiations of C3H 10T1/2 cells adjacent to the gold surface resulted in increased rates of oncogenic transformation. A dose of 100 mGy 80 kV X rays (measured in homogeneous PMMA) caused a frequency at an inserted gold surface comparable to that obtained with a dose of about 4.5 Gy of 60Co gamma rays in homogeneous PMMA.

Gold nanoparticles as novel agents for cancer therapy

“…Using physical dosimetry, Regulla et al [65] demonstrated massive DEFs of 55-114 when detectors were placed next to gold foil encased in polymethylmethacrylate (PMMA) and irradiated with mean X-ray energies of 33-100 kV. With 80 kV X-rays, the secondary radiation decreased exponentially with the distance from the gold foil and was negligible at 30 mm.…”

Cell type-dependent uptake, localization, and cytotoxicity of 1.9 nm gold nanoparticles

“…[12][13][14] A tissue modeling study using gold foil reported a dose enhancement factor of 50 due to the production of secondary electrons generated from low-energy photon irradiation. 15 Subsequent progression to produce smaller particles, thereby increasing the gold surface area to volume ratio, resulted in the production of gold particles in the nanometer range. Hainfeld et al 6 detailed the first study using 1.9 nm gold nanoparticles as radiosensitizers.…”

Evaluation of cytotoxicity and radiation enhancement using 1.9 nm gold particles: potential application for cancer therapy

“…Theoretical simulations have shown gold (Z = 79) compounds as ideal radiation enhancing agents [15][16][17]. Several experimental attempts have been made to exploit the radiation enhancing properties of gold for therapeutic benefit using gold foils [18,19] and microparticles [20].…”