Uveal melanoma clonogenic response to proton beam irradiation

Purpose The goal of this study was to compare the cellular clonogenic response to proton beam and X‐ray irradiation of uveal melanoma cell line Mel270 and human melanoma cell line BLM. Methods BLM line was derived from a skin melanoma metastasis to the lung, and Mel270 is a primary uveal melanoma cell line. Cells were irradiated with 1–5 Gy of X ray (300 kVp Phillips, 1 Gy/min) or proton beam (60 MeV) from Proteus C‐235. After irradiation cells were seeded for the clonogenic assay. Two weeks after seeding the number and type of clones were determined. Three types of clones were found: the largest in size holoclones (with the highest potential to proliferate), medium sized meroclones and the smallest paraclones (low potential to proliferate). Results The total number of clones were similar for both cell lines and both types of irradiation. The RBE values calculated for 37% of survival fraction were 1.11 and 1.13 for Mel270 and BLM cells, respectively. Three types of clones seen in untreated cultures imply the heterogeneity of cellular populations. After irradiation the proportion between the three types of clones was changed: the number of holoclones was drastically lower, and the number of paraclones increased. The number of paraclones was lower after proton bean irradiation in comparison to X‐rays in both cell lines. Conclusions Proton beam and X‐ray irradiation differently modify the proliferation potential of melanoma cells.