Auger electrons and radiation therapy

Recent development in radiation therapy led to the generation of a variety of quantum beams that are showing promise for cancer therapy. Conventional radiation therapy uses X-rays, while more recent therapies use protons and heavy atoms such as carbon ions. Neutrons are used in boron neutron capture therapy. Decay of radioactive species generates α-rays, β-rays, or Auger electrons, These quantum beams have the ability to cause DNA damage including double-strand breaks which induce cancer cell apoptosis. At Kyoto University, we have developed a new method to generate the Auger electrons inside human cancer cells. Our approach uses nanoparticles that are efficiently taken up and localized just outside of cell nucleus. This places high Z atoms close to DNA. We developed two types of high Z atom-containing nanoparticles; one containing gadolinium and the other containing iodine. We used these nanoparticles to distribute gadolinium or iodine throughout tumor spheroids, three-dimensional mass of cancer cells. Tumor spheroids containing gadolinium or iodine were then irradiated with synchrotron generated monochromatic X-rays. This caused generation of DNA double strand breaks, apoptosis induction and disruption of tumor spheroids. Interestingly, we noted that an optimum energy level of the monochromatic X-ray is needed to cause maximum effect. (author)