Abstract
According to the depth of the cancer in a body, three different accelerated energy of carbon beams; 290, 350, 400 MeV/u are used for therapy at HIMAC. The difference in biological effectiveness by the difference in the accelerated energy is however not well known. We measured biological effectiveness for different energy of carbon beams with the same SOBP (Spread Out Bragg Peak) to evaluate the difference.
We have measured the physical characteristics of the beams, and perform biological experiment. Here, we used human salivary grand tumor originated HSG cells that have been used to measure biological effectiveness for particle beams. We used 290 and 400 MeV/u carbon beams at proximal (-25 mm), middle (0), distal (+25 mm) and distal end (+28 mm) in the 60 mm SOBP beam. Cells were exposed to the beam at those position and applied conventional cell survival assay after 14 days after irradiation. The survival curves were fitted to Linear-Quadratic model, and D10 dose and RBEs to 200 kV X-rays were obtained.
Physical depth-dose distribution to the depth was steeper in the SOBP at 290 MeV/u compared to that at 400 MeV/u. In the other hand, depth-RBE distribution was increases tenderly to 290 MeV/u than that to 400 MeV/u beam. Finally the uniformity of the biological effectiveness (Dose x RBE) becomes flat as well as pre-clinical study at start of HIMAC clinical trial. Both biological uniformity and absolute biological efficiency to the 290 and 400 MeV/u beams were similar each other.
