Radiosensitivity in mesothelioma cell lines for X rays and carbon-ion beams

Malignant pleural mesothelioma (MPM) is an aggressive tumor arising from serous surfaces and often related to asbestos exposure. Taking into account a latency period of 20-40 years, it has been estimated that the number of men dying from MPM increase each year until a peak is reached in about 2020. MPM is resistant to various forms of therapy, such as radiotherapy, surgery or chemotherapy, and only slightly improve prognosis. So far, no effective therapeutics including chemotherapy or radiotherapy has been established for the disease-advanced case. The present study was carried out in order to examine the radiosensitivity of MPM cell lines by X rays and carbon-ion beams. Officially distributed 6 kinds of MPM cell lines were used and irradiated with X rays or carbon-ion beams (13.3 keV/μm and approximately 80 keV/μm) at the Heavy Ion Medical Accelerator in Chiba (HIMAC). Cell-killing effect was detected using a colony-formation assay. D₁₀, which is one of the parameters for cellular radiosensitivity, of 6 cell lines ranges from 2.74 Gy to 5.42 Gy for X rays, 2.17 Gy to 4.21 Gy for 13 keV/μm- and 1.08 Gy to 2.38 Gy for 80 keV/μm-carbon ions. The relative biological effectiveness (RBE) values calculated by the D₁₀ relative to X rays, ranges from 1.24 to 1.42 for 13 keV/μm- and from 2.31 to 3.09 for approximate 80 keV/μm-carbon ions on each cell line. The results suggest that the irradiation of high LET carbon ions are also significantly more effective in cell killing for the 6 kinds of MPM cell lines than that of low LET X rays. (author)