Design and development of a new micro-beam treatment planning system: effectiveness of algorithms of optimization and dose calculations and potential of micro-beam treatment.

A new treatment planning system (TPS) was designed and developed for a new treatment system, which consisted of a micro-beam-enabled linac with robotics and a real-time tracking system. We also evaluated the effectiveness of the implemented algorithms of optimization and dose calculations in the TPS for the new treatment system. In the TPS, the optimization procedure consisted of the pseudo Beam's-Eye-View method for finding the optimized beam directions and the steepest-descent method for determination of beam intensities. We used the superposition-/convolution-based (SC-based) algorithm and Monte Carlo-based (MC-based) algorithm to calculate dose distributions using CT image data sets. In the SC-based algorithm, dose density scaling was applied for the calculation of inhomogeneous corrections. The MC-based algorithm was implemented with Geant4 toolkit and a phase-based approach using a network-parallel computing. From the evaluation of the TPS, the system can optimize the direction and intensity of individual beams. The accuracy of the dose calculated by the SC-based algorithm was less than 1% on average with the calculation time of 15 s for one beam. However, the MC-based algorithm needed 72 min for one beam using the phase-based approach, even though the MC-based algorithm with the parallel computing could decrease multiple beam calculations and had 18.4 times faster calculation speed using the parallel computing. The SC-based algorithm could be practically acceptable for the dose calculation in terms of the accuracy and computation time. Additionally, we have found a dosimetric advantage of proton Bragg peak-like dose distribution in micro-beam treatment.

Size, concentration and incubation time dependence of gold nanoparticle uptake into pancreas cancer cells and its future application to X-Ray Drug Delivery System.

One of the restrictions in the potential use of gold markers for medical imaging/tracking of harder tumors is its size. We propose to use gold nanoparticles which, due to its small size, can be administered conveniently via intravenous injection. One of the factors that determine the clinical utility of nanoparticles is the ability to enter cells. In this report, the stability of gold nanoparticles mixed with different media was determined by UV-vis spectroscopy. Gold nanoparticle size was confirmed by TEM. Intracellular uptake using different gold nanoparticle sizes, incubation times and concentrations were analyzed using Atomic Absorption Spectrometry (AAS). Temperature dependence uptake was also measured using AAS. The results showed that pancreas cancer cells uptake 20 nm gold nanoparticles preferentially compared to other gold nanoparticle sizes. Efficient accumulation of gold nanoparticles into pancreas cancer cells can be achieved at longer incubation time and higher concentration. The findings of this study will help in the design and optimization of the gold nanoparticle-based agents for therapeutic and diagnostic applications of X-ray Drug Delivery System.

Numerical evaluation of the effectiveness of colloidal gold as a contrast agent.

Monte Carlo numerical simulations were conducted to evaluate the effectiveness of colloidal gold as a contrast agent. The simulations were conducted using a simple configuration, modeling a phantom to maintain the generality of the results, and the effects of the mass percentage of gold accumulated inside the tumor and the energy of the irradiating X-rays were evaluated, as well as other information, such as the energy spectrum of the photons reaching the detector and the change in the energy deposited inside the phantom. The contrast of the X-ray image due to the layer is calculated from the total energy of photons transmitted to the back surface of the phantom. The simulation revealed that colloidal gold with a mass percentage of 1.0% provided an image for which the contrast was almost 70% of that for bone of the same thickness when X-rays from conventional X-ray tubes were considered. Monochromatic X-rays of 44, 66, and 88 keV, which simulated the Compton scattering monochromatic X-ray source being developed, were also evaluated. X-rays at the first two energies did not have a significant advantage over the rays from the X-ray tubes. For colloidal gold with a mass percentage of 1.0%, the 88 keV monochromatic X-ray produced an image contrast that was about 10% higher than the contrast for bone of the same thickness, as suggested by the K-absorption energy of gold. However, the improvement was not large considering the difficulty involved in making such a high-energy monochromatic X-ray source available.