Masakazu Hara

Improvement of Three-dimensional Monte Carlo Code PHITS for Heavy Ion Therapy

The general purpose particle and heavy ion transport code, PHITS, was modified for improved analysis of dose distribution in carbon therapy systems. We added two new functions into PHITS, one for an energy dispersion calculation and the other for transport in an AC magnetic field, which enabled 3-dimensional modelling of a carbon therapy system for the first time. With this code we calculated the dose distribution in a carbon therapy system, and these results showed good agreement with experimental data. This improved version of PHITS is a valuable tool for the design of carbon therapy aperture or for the estimation of the dose distribution in treatment planning.

Hyperthermia and chemotherapy using Fe(Salen) nanoparticles might impact glioblastoma treatment

We previously reported that μ-oxo N,N’-bis(salicylidene)ethylenediamine iron [Fe(Salen)], a magnetic organic compound, has direct anti-tumor activity, and generates heat in an alternating magnetic field (AMF). We showed that Fe(Salen) nanoparticles are useful for combined hyperthermia-chemotherapy of tongue cancer. Here, we have examined the effect of Fe(Salen) on human glioblastoma (GB). Fe(Salen) showed in vitro anti-tumor activity towards several human GB cell lines. It inhibited cell proliferation, and its apoptosis-inducing activity was greater than that of clinically used drugs. Fe(Salen) also showed in vivo anti-tumor activity in the mouse brain. We evaluated the drug distribution and systemic side effects of intracerebrally injected Fe(Salen) nanoparticles in rats. Further, to examine whether hyperthermia, which was induced by exposing Fe(Salen) nanoparticles to AMF, enhanced the intrinsic anti-tumor effect of Fe(Salen), we used a mouse model grafted with U251 cells on the left leg. Fe(Salen), BCNU, or normal saline was injected into the tumor in the presence or absence of AMF exposure. The combination of Fe(Salen) injection and AMF exposure showed a greater anti-tumor effect than did either Fe(Salen) or BCNU alone. Our results indicate that hyperthermia and chemotherapy with single-drug nanoparticles could be done for GB treatment.

Visualization of magnetic microparticles in liquid and control of their motion using dynamic magnetic field

Visualization technique of micro- or nanoparticles with sufficient spatial and temporal resolutions is required for quantitative study of motion of magnetic particles and their control using a dynamic magnetic field. Based on the particle tracking velocimetry method, a visualization system of micron-size particles has been developed. A proof-of-concept experiment of controlling magnetic particles using a dynamic magnetic field was made, and motions of magnetic particles under a dynamic magnetic field were visualized successfully using the developed system: the motions of particles synchronizing with the applied dynamic magnetic field could be observed.

The Behavior of Nano- and Micro-Magnetic Particles Under a High Magnetic Field Using a Superconducting Magnet

Magnetic force has been used for drug delivery, magnetic separation, and other kinds of micro- and nano-particle handling. As fundamental studies of these applications, we have investigated the visualization of the motion of micro-magnetic particles under a dynamic magnetic field. We have also studied the contactless grasp of a micro-magnetic particle suspended in a fluid by using coil currents. In the study, we have developed a method for quantitatively estimating the influencing forces. However, these experiments have limitations in the magnetic field strength of normal conducting electromagnets or permanent magnets. Therefore, much higher magnetic force is needed for the application to drug delivery or cell/DNA manipulation. High magnetic field generating high magnetic force saturates the magnetization of magnetic particles during the particle control, and the magnetic saturation influences the particle behavior. However, such behavior of magnetic particles has not been sufficiently studied yet. In this paper, the behavior of the particles nearly or fully saturated under the high magnetic field of a superconducting magnet was visualized successfully, and ferrite and feeble magnetic particles were introduced in order to gain insight into their behavior.