Physical engineering (Graduate School of Science and Technology)

　 Electron density distribution in the patient body is important for precise treatment planning in heavy ion radiation therapy. That is because the stopping power of charged particles is proportional to the electron density. Therefore, a new X-ray CT system (photon counting CT) is developed and a method to measure accurate electron density distribution in the human body is studied.

　 The program is advancing the study of microcantilever biosensor and silicon nanowire biosensor, which are developed by nano- and micro-scale fabrication technology using electron beam and ion beam. In the previous study, the antigen and antibody with ultra-low concentration at femtomolar level (fM=10^-15 mol/L) has been successfully detected, which contains only 100 target molecules in a drop of solution. In addition, with an aim of improving for selection of good quality embryo and birthrate under fertility treatment, world-leading technology for measuring an in vitro fertilized embryo mass with high mass sensitivity is being studied.

　 Futuristic quality control and assurance of heavy ion radiation cancer treatment strongly rely on the spatial- and energy-resolution of dosimeters utilized in the treatment field, since such as next generation technologies including multiple ion radiation method or LET (Linear Energy Transfer) painting technology are soon going to be implemented. Those requirements drive research and development on a new-generation of dosimeter which based on a semiconductor with better energy resolution and potentially good spatial resolution. Those dosimeters based on semiconductor well respond to wide-range of LET therefore it could also consider to implement the differences in RBE (Relative Biological Effectiveness) into dose estimation, which largely differed at the point of Bragg peak by reflecting differences in LET. Wide band-gap semiconductor such as diamond or silicon carbide (SiC) is a candidate substrate of such dosimeter with their advanced radiation tolerance. Under the international collaboration with University of Wollongong in Australia, world-wide leading laboratory of medical radiation physics and dosimeters, we are developing dosimeter system for such LET measurement from sensor head to peripherical circuits as well as data processing system.

　 Heavy ion irradiation to cancer cells causes damage to the genomic DNA in the cancer cells. This DNA damage induces the death of the cancer cells. DNA repair mechanisms counter this treatment and help cancer cells survive. Therefore, we are trying to clarify the human DNA repair mechanism using various human cultured cells. Research on cancer immunotherapy and development of cancer vaccine is another of our projects. We will establish an inexpensive production system that supplies safe cancer vaccines using transgenic silkworms. By analysing intracellular signalling, we are also trying to clarify the response of cancer cells to several stimuli. For example, we analyse how cancer cells adapt to an acidic environment as tissues around the cancer become acidic.

　 Recently growing interest are being paid for advanced clinical application of radiation including heavy ion cancer therapy or hadron therapy as advanced cancer treatment technology. Also the boundaries of clinical treatment and diagnosis tend to disappear while such other clinical diagnosis utilizing radiation are often used during clinical treatment (Interventional Radiology; IVR). Those trends is causing an immediate issues of unnecessary and undesired local radiation exposure which should be avoided for both health care providers and patients. However, as seen under the current situation dosimetry corresponding the issues are well not established up until now. For example, the dosimetry on local exposure of eye lenses, which recommended to be reduced in ICRP Publications 2011, has been not regulated. Here we are tackling the issues by developing optically functionated convenient radiation dose monitoring device based on inexpensive phosphate glass that enables usage at various radiation fields of X-, gamma -rays, etc. An eyeglass type wearable dosimeter (refer to figure) is an example. The figure example shows the response of wearable glass dosimeter when the left eye is exposed X-rays with different exposure time, simulating the case when a doctor assumes to be exposed highly-energetic photon under CT treatment. Gunma University aims for implementation of a such convenient and yet high-precision dosimeter by collaborating with companies and research institutes which are leading the field in Japan such as the National Institute of Radiological Sciences and other laboratories.