Intercomparison of Radiobiological RBE among Japanese Proton Therapy Facilities

PTCOG4

RBE Intercomparison of Proton Beams at Five Radiotherapy Facilities in Japan

Five proton therapy facilities (HIBMC, Hyogo; NCCHE, Kashiwa; WERC, Tsuruga; PMRC, Tsukuba; SCC, Shizuoka) are now working in Japan. Prior to starting the clinical use of proton-beams for cancer therapy, we have investigated the relative biological effectiveness (RBE) to high-energy X-rays. The RBE values were determined to estimate the clinical doses for each therapeutic facility. Spread-out Bragg peak (SOBP) beams having 60 mm depth were obtained from 180 MeV (WERC), 200 MeV (PMRC) or 190 MeV (the others) proton beams with the same way to the patient therapy at each facility. Human salivary gland tumor cell (HSG) that has used at the pre-clinical radiobiological studies (RBE determination) for HIMAC carbon beams was used. We obtained D10 values by means of in vitro colony formation assay after single-dose exposures of proton-beams. The RBE values of each beam were obtained by comparing the D10 values to that for 4-6 MeV linac X-rays at each facility. The D10 values for high energy X-rays showed no significant differences among the facilities tested. The average RBE value for proton beams at the middle position of the SOBP was 1.03 +/- 0.02 (mean +/- SD). The values may be slightly lower at the entrance position of the SOBP, and a little higher at the distal position of the SOBP than that at middle position for each facility. The depth-dose distribution of all the SOBP beams has designed and obtained very well, and showed good uniformities of biological dose distribution for all facilities.12th International Congress of Radiation Researc

Intercomparison of Radiobiological RBE Among Japanese Proton Therapy Facilities

INTRODUCTIONHIMAC (Heavy-ion Medical Accelerator in Chiba) has constructed in 1993, and clinical trials has started in 1994 together with academic research activities, including physics, engineering, and biology. Pre-clinical radiobiological studies have performed to estimate clinical RBE for hadron beams. Following the HIMAC, several hadron therapy facilities (HIBMC, Hyogo; NCCHE, Kashiwa; WERC, Tsuruga; PMRC, Tsukuba; SCC, Shizuoka) have started the therapy in Japan. We have evaluated the RBE of each hadron beams for all the facilities with the same biological system and technical staffs as well as at HIMAC. METHODSHuman salivary gland tumor cells (HSG) were used for the studies. All experiments were performed with single-dose exposures for both proton beams and linac X-rays at each facilities. All 60 mm SOBP beams were generated from 180-190 MeV proton beam, and the energy of high-energy linac X-rays were 4-6 MeV, but it depends on the facilities. Samples were placed at the plateau position or the entrance, middle, or proximal positions of SOBP beam or at the 50 mm depth position of the linac beam. The D10 values from survival curves by the colony formation assay were obtained. The RBE values of proton beams were calculated to X-ray data. RESULTSThe average RBE at the middle of SOBP beam from all facilities was 1.030+/-0.017 (mean +/- SD). Flatness of the RBE in the SOBP were slightly disposed to increase with the depth. The values were slightly lower at the entrance, and little bit higher at the distal than that at the middle position. DISCUSSIONX-ray data showed very good agreement and the deviations were less than 2 % among the facilities. The RBE values also showed good agreement among the facilities with 2 % or less standard deviation. Some difficulties were found in the irradiation systems, i.e. the dose determination and/or geometrical sample setting methods are different among the facilities. This may makes difficult exact comparative judgments of the radiobiological data. During the radiobiological experiments process, several problems were found and have solved. In this point of view, preclinical experiments were important as a simulation of patient treatments. CONCLUSIONThe RBE values for all proton therapy facilities in Japan were similar (1.02) with small deviation. The depth-dose distribution of all the SOBP beams has designed very well, and showed good uniformities of biological dose at all facilities. Physical dosimetry system should be unify for all the facilities to compare the results.WC200