• Text in Japanese

Development of new particle beam therapy methods based on physical and biological characteristics of heavy ions

The lab conducts basic research on the biological effects of carbon ion therapy against various tumors and various tissues. These data are taken into consideration for determining a radiotherapy treatment planning, including the carbon dose distribution needed for particular cell types.

Proton and carbon ions used in particle beam therapy are most effective at a certain depth, which can be adjusted based on the amount of energy applied, but reach a maximum depth known as the Bragg peak. Therefore, it is possible to increase the dosage of the beam to deep seated tumors and, conversely, decrease the dosage to limit the beam to shallow regions (Fig. 1).

Fig. 1 Dose-depth distribution of the particle beam. Increasing the concentration dose to deep seated tumors while decreasing the dose to limit the beam to shallow regions.

In carbon ion beam therapy, a dose distribution calculation is performed to estimate the distribution of radiation in the body. During treatment planning, the dose distribution is calculated by multiplying the physical dose of the particle beam by the biological and the clinical effects (Fig. 2). Dose distribution is calculated for all tumors and normal tissues based on data obtained from experiments performed on human salivary gland cancer cells. However, it should be noted that human salivary gland cancer cells may not be fully representative of all cancers and normal tissues. Thus, the biological effect will vary depending on the type of tumor to be treated.

Fig. 2 Concept of carbon ion beam dose distribution. The dose is calculated with physical dose of the particle beam multiplied by the biological and clinical effects.