一般雑誌記事 Hadrontherapy enhanced by combination with heavy atoms: Role of Auger effect in nanoparticles. In: CHAPTER 14, Nanobiomaterials in Cancer Therapy: Application of Nanobiomaterials. Vol.7

Usami, N.  ,  Kobayashi, K.  ,  Furusawa, Y.  ,  Le Sech, C.

内容記述
A great deal of effort is dedicated to cancer therapies because these diseases are one of the most frequent causes of morbidity or death in human society and represent a challenge for treatment. Different therapeutic methods have been proposed for a long time to treat solid malignant tumors, including the use of ionizing particles. Radiation therapy has the advantage of being less invasive, in contrast to surgical treatment. However it can lead to the possible induction of a secondary tumor. Because of the relatively non-invasive nature of radiation therapy, less physiological and psychological burden is placed on patients compared to other treatments like surgery or chemotherapy involving cytotoxic drugs. For these reasons, recovery is more rapid after radiation therapy than from other protocols. Although it is not a ubiquitous treatment of all types of cancers, radiation therapy is often considered to be the first choice for treatment, with possible combination with an additional protocol dedicated to prevent metastasis from the primary tumor. Intensive studies are presently concerned with this subject to improve its therapeutic index. Radiotherapy using atomic ions has been proposed under the name hadrontherapy. In nuclear physics hadrons are particles made of quarks. Protons or neutrons are made of three quarks belonging to this family. In medical practice proton or carbon therapy is called hadrontherapy, though the latter ion is not strictly speaking a hadron. Ion therapy has the well-known advantage of dose deposition represented by the Bragg peak compared to the dose profile observed with photons. It is now an important tool to treat tumors. Details on the treatment and their results can be found in the review paper by Tsujii et al. (2007). However, in medical practice, the Bragg peak is spread out (SOBP) as shown in Figure 14.6, to obtain a homogeneous dose in the target volume. When the SOBP mode is used the dose in the healthy tissues in the entrance channel is not negligible. The possibility of enhancing the effects of the dose at the Bragg peak in the SOBP mode is of obvious interest. Previous experiments performed to study the biological effects following the irradiation by carbon or helium ions of mammalian cell, loaded with molecules containing platinum atoms (platinum salt), have shown that the cell death rate augments when high-Z atoms are present, resulting from an increased production of free radicals (Usami et al., 2008). This finding suggests that, assuming a selective uptake of high-Z atoms in the cancerous cell, the efficiency of the irradiation by atomic ions to induce cell death should be augmented. Thus the combination of irradiation by atomic ions and addition of compounds containing high-Z atoms in the cells might be of interest for therapeutic purposes.The purpose of this chapter is to review the studies of radiobiological effects from a mechanistic perspective. Although these are basic studies, some ideas emerging from these results should lead to new developments that could be introduced into medical practice in the near future in order to enhance the effectiveness of radiation therapies.

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