Analysis of Redioresistant Tumor by Heavy Particle Irradiation

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The tumors are sometimes resistant to radiotherapy or regrow after regression by radiotherapy. These tumors are expected to have residual viable tumor cells in the tumor and easily regrow the tumor cells. This phenomenon may depend on the higher of repair of the damaged DNA or accelerated capability facility of the residual tumor cell. There are several differences of biological responses between tumor cells exposed to the X-rays and to the heavy particles. This phenomenon is expressed as relative biological effectiveness (RBE). When the tumor cells are irradiated with heavy particles of same LET and same doses, RBEs depend on each tumor cell line. This study was performed to develop the method to estimate the radiosensitivity of the tumor cell to X-ray irradiation from the radiosensitivity to heavy particles. In this study, 8 in cell lines those are established from adenocarcinoma of the ovarian cancer or cervical cancer, 6 cell lines established from squamous cell carcinoma of the es … More ophageal cancer and one from malignant melanoma were irradiated with X-rays. The radiosensitivity was determined by the colony forming assay. The cells established from human tumors were different from those from the animal tissues. The former cells had smaller Do and n values than the latter, and showed steeper cell survival curves. There was no significant difference between cell lines from adenocarcinoma and those from squamous cell carcinoma. When the cells were irradiated with carbon beams or neon beams, they showed the same survival curves for the same LET and same doses. The mutation of DNA that was induced by heavy particle irradiation was determined by the expression of hypoxanthine-guanine phosphrybosyl transferase (hprt) locus. The frequency of expression of hprt locus was completely different between carbon beam irradiation and neon beams. There was no significant difference of radiosensitivity between carbon beams and neon beams, but carbon beams induced higher mutation than neon beams. This result suggests that neon beams may be useful in clinical radiotherapy. Less