Wan Nordiana Rahman

Potential dependent superiority of gold nanoparticles in comparison to iodinated contrast agents

PURPOSE To identify the benefits in image contrast enhancement using gold nanoparticles (AuNPs) compared to conventional iodinated contrast media. MATERIALS AND METHODS Gold nanoparticles and iodinated contrast media were evaluated for contrast enhancement at various X-ray tube potentials in an imaging phantom. Iopromide and AuNP suspension were equalized according to molar concentration of radiopaque element (0.5077 Mol/L). Contrast-to-noise ratio is used to quantify contrast enhancement. Both projectional radiographic (40-80 kVp) and computed tomography (CT) (80-140 kVp) imaging modalities were examined. RESULTS AND CONCLUSIONS Findings indicate 89% improvement in CNR at low energies near the mammographic range (40 kVp). However, as expected no significant difference in enhancement was observed at potentials commonly used for angiography (around 80 kVp) probably due to the k-edge influence for iodine. At the highest energies typically available in computed tomography, significant improvement in contrast enhancement using gold nanoparticles is obtained, 114% greater CNR than that produced by iodine at 140 kVp. Experimental findings for 70-120 kVp spectra correlate well with the theoretical calculations based on linear attenuation coefficients. Superior attenuation of gold nanoparticles at low and high kVp potentials support their further (pre)clinical evaluation.

Optimal energy for cell radiosensitivity enhancement by gold nanoparticles using synchrotron-based monoenergetic photon beams

Gold nanoparticles have been shown to enhance radiation doses delivered to biological targets due to the high absorption coefficient of gold atoms, stemming from their high atomic number (Z) and physical density. These properties significantly increase the likelihood of photoelectric effects and Compton scattering interactions. Gold nanoparticles are a novel radiosensitizing agent that can potentially be used to increase the effectiveness of current radiation therapy techniques and improve the diagnosis and treatment of cancer. However, the optimum radiosensitization effect of gold nanoparticles is strongly dependent on photon energy, which theoretically is predicted to occur in the kilovoltage range of energy. In this research, synchrotron-generated monoenergetic X-rays in the 30–100 keV range were used to investigate the energy dependence of radiosensitization by gold nanoparticles and also to determine the photon energy that produces optimum effects. This investigation was conducted using cells in culture to measure dose enhancement. Bovine aortic endothelial cells with and without gold nanoparticles were irradiated with X-rays at energies of 30, 40, 50, 60, 70, 81, and 100 keV. Trypan blue exclusion assays were performed after irradiation to determine cell viability. Cell radiosensitivity enhancement was indicated by the dose enhancement factor which was found to be maximum at 40 keV with a value of 3.47. The dose enhancement factor obtained at other energy levels followed the same direction as the theoretical calculations based on the ratio of the mass energy absorption coefficients of gold and water. This experimental evidence shows that the radiosensitization effect of gold nanoparticles varies with photon energy as predicted from theoretical calculations. However, prediction based on theoretical assumptions is sometimes difficult due to the complexity of biological systems, so further study at the cellular level is required to fully characterize the effects of gold nanoparticles with ionizing radiation.

Dosimetry And Its Enhancement Using Gold Nanoparticles In Synchrotron Based Microbeam And Stereotactic Radiosurgery

Research into the areas of synchrotron generated microbeam radiotherapy (MRT) and stereotactic radiosurgery is increasing. Such MRT techniques are showing potential of tackling some of the more difficult radiotherapy cases such as certain type of brain tumours. Two challenging aspects of these techniques are addressed in this investigation; the difficulty of dose determination and the delivery of the treatments at lower dose levels. In this research polymer gels were used as phantoms and dosimeters and cells were used to confirm outcomes. Normoxic polyacrylamide gels (nPAG) were tested as potential dosimeters for microbeam dosimetry. Following irradiation using microbeam and minibeam radiation from the BL28BU beam-line at Spring-8, Japan, the nPAG were scanned using a Raman spectroscopy technique. Dose enhancement caused by the inclusion of the gold nanoparticles (AuNPs) in the target was investigated using both cells and polymer gels. The use of AuNP could potentially reduce the dose required for the delivery of MRT. In this study it was shown that using endothelial cells with AuNPs, the minimal dose for clear cell killing along the beam line was reduced to 10 Gy. Both studies cell and gel studies indicates significant dose enhancement caused by the gold atoms in the target.

Effect of scanning parameters on dose-response of radiochromic films irradiated with photon and electron beams

Proper dosimetry settings are crucial in radiotherapy to ensure accurate radiation dose delivery. This work evaluated scanning parameters as affecting factors in reading the dose-response of EBT2 and EBT3 radiochromic films (RCFs) irradiated with clinical photon and electron beams. The RCFs were digitised using Epson® Expression® 10000XL flatbed scanner and image analyses of net optical density (netOD) were conducted using five scanning parameters i.e. film type, resolution, image bit depth, colour to grayscale transformation and image inversion. The results showed that increasing spatial resolution and deepening colour depth did not improve film sensitivity, while grayscale scanning caused sensitivity reduction below than that detected in the Red-channel. It is also evident that invert and colour negative film type selection negated netOD values, hence unsuitable for scanning RCFs. In conclusion, choosing appropriate scanning parameters are important to maintain preciseness and reproducibility in films dosimetry.

SU-DD-A3-05: Radiosensitization of Endothelial Cells Model Using Gold Nanoparticles for Microbeam Radiotherapy

Purpose: Microbeam radiotherapy(MRT) is a technique that use array parallel thin (<100μm) slices of synchrotron generated x‐ray beam. In this study, we investigated the radio‐sensitizing effects of goldnanoparticles (AuNps) on endothelial cells culture model in combination with irradiation of MRT.Method and Materials: Bovine aortic endothelial cells (BAECs) were cultured as a confluent monolayer on a 2 well chamber slides with 0mM, 0.5 mM and 1.0mM of AuNps. The cells were irradiated with 10 Gy of synchrotron generated x‐ray beam of median energy 150 kVp. Each microbeam is approximately 30 microns wide with a spacing of 200 microns between adjacent microbeams. Gafchromic films were attached to the cells culture slide to verify the dose received by the cells. The experiments were performed on the BL28B2 beamline at the SPring8 Synchrotron Japan. The cells were then fixed at 6, 12 and 24 hours after irradiation and were imaged using phase contrast microscope. Cells viability assays using tryphan blue exclusion method were performed after 24 hours of irradiation. Results: The observations under phase contrast microscopy show all the cells were dead at the area of irradiation. Samples with AuNps clearly showed the path of microbeam which is visible as a straight line compared to the samples without AuNps. There are some neighbouring cells start to migrate to the irradiated area, filling the gap for both samples. The cells viability results showed the dose enhancement effects where only 52% cells survived for 0.5 mMol AuNps and only 18% survive for 1mMol AuNps when irradiated with microbeam. These results were expressed as percentage relative to the control samples. Conclusion: The results demonstrate that the AuNps are effective radiosensitizer that will increase the therapeutic efficacy of MRT.

SU-GG-I-157: Quantification of Radiographic Image Contrast Enhancement Using Gold Nanoparticles

Purpose: To quantify radiologic imagecontrast enhancement using goldnanoparticles compared to iodinated contrast media (CM) over the entire diagnostic range of x‐ray energies. Method and Materials: A Perspex phantom with 4mm cylindrical wells was used to simulate small portions of vasculature. Each well was loaded with either goldnanoparticle solution or iodinated CM at equal concentration (0.5077 M radiopaque element). The phantom was imaged under full scatter conditions in computed radiography(CR) (40–80 kVp) and computed tomography(CT) (80–140 kVp). Images obtained at low energies (≈ 40 kVp) were validated using diagnostic type gafchromic film (Gafchromic® XRQA). CdTedetector with MCA was used to obtain transmission spectra after x‐ray beam at 130 kVp passed through solutions of goldnanoparticles or iodinated CM. Results:CT and CRimages were evaluated for contrast enhancement by contrast‐to‐noise ratio (CNR). Low energy results support previous findings, with gold exhibiting a 60% greater CNR than iodine. Goldnanoparticles also displayed excellent imagecontrast in CT, producing over two times greater signal than iodinated CM at 140 kVp. Over the x‐ray energy range of 70–100 kVp, however, both samples displayed similar contrast values. CdTe attenuation spectra are in accordance with image results where goldnanoparticles show a greater probability of attenuation than iodine for photons below approximately 35 keV and above 80 keV. Conclusion: Data indicates that a solution bearing goldnanoparticles would be an effective alternative to iodinated CM diagnostic radiology particularly at lower and higher ends of x‐ray energies used in radiology, such as mammography and CT.Conflict of Interest (only if applicable): Funding provided by NanoVic (Nanotechnology Victoria, Ltc.)

SU‐GG‐J‐162: Radiosensitization by Gold Nanoparticles in Superficial Radiotherapy Techniques

Purpose: To investigate the radiosensitization of superficial kilovoltage range of x‐ray energy and megavoltage electron beams due to the presence of goldnanoparticles (AuNps) using cell survival curves and normoxic polyacrymide gel (nPAG). Method and Materials: Bovine aortic endothelial cells (BAECs) with and without AuNps were irradiated with kilovoltage superficial x‐ray beams and megavoltage electron beams. Cell survival at various concentrations of AuNps (0.25mMol–1mMol) was measured using colorimetric assay. Level of dose enhancement for x‐ray and electron beams was also quantified using AuNps doped nPAG. Results: AuNps enhanced the cells killing up to 21 fold for 1mMol of AuNps irradiated with 80 kVp x‐ray beams. Maximum dose enhancement factor (DEF) of 4.63 was measured for 12 MeV electron beams in the presence of 1mMol AuNps. 80 kVp which represents effective beam energy of around 40 keV was the optimum energy found that yield highest enhancement ratio. Measurements using AuNps doped nPAG also exhibit higher polymerization resulting from increased photoelectric interactions, Auger electrons and characteristic x‐ray generation. The experimental dose enhancements obtained were also in agreement with theoretical calculation and those previously documented for iodine atoms. Conclusion: Both experiments with cell culture and nPAG confirm that AuNps are able to enhance the radiationdose for x‐ray and electron superficial therapy. Lower doses from external sources are required to produce the same radiation effect with AuNps compared without application of AuNps. This will lead to improvement in superficial radiotherapy techniques of both x‐ray and electron. The use of this technique with microbeam radiotherapy technique and kilovoltage type intraoperative radiotherapy techniques are now under investigation in our group.