Biological Effects of Heavy Ion Beam on Human Breast Cancers

BACKGROUND: Radioresistance of the extensive intraductal component (EIC) is amajor limiting factor in breast conserving therapy (BCT). The purpose of the present experiment was to elucidate the biological effects of a carbon beam on human breast cancer cell lines in order to evaluate its clinical benefits in BCT. METHODS: Human breast cancer cell lines, both grown in culture and inoculated into nude mice were subjected to X-ray (200 kV) and heavy ion beam (290 MeV/u carbon beam) irradiation. The relative biological effectiveness (RBE) of the carbon beam and X-ray irradiation was determined at the level of D10 (10% survival dose) on the dose-survival curve. By using a colony forming assay the survival curves of the three cultured cell lines (YMB-I, OUUB-M, CRL-1500) at a linear energy transfer (LET) of 80 keV/µ m were obtained. Cancer established in nude mice was exposed to single-dose and triple-fractionated irradiation at a LET of 50 keV/µm. The growth of tumorsat various doses was observed and the survival curves were determined using thetumor regrowth assay. RESULTS: The RBE of the carbon beam on each cell line ranged from 2.17 to 2.89 (2.59+/-0.37). That of the tumor in nude mice was 1.53 and 2.00 on exposure to single-dose and fractionated irradiation, respectively. CONCLUSION: Human breast cancer cell lines showed high intrinsic sensitivity to a carbon beam and its effects on the tumor were enhanced by fractionated irradiation. It is worthy using carbon beam is applied to use for clinical trials inBCT.