Prognostic factors in Uveal Melanoma

Purpose: To investigate the effects of split dose irradiation on primary and metastatic uveal melanoma cell lines using a clonogenic survival assay. Methods: Appropriate cell concentrations of four primary and four metastatic human uveal melanoma cell lines were cultured for irradiation with single doses and with two equal fractions separated by 5 h. After irradiation colony formation was allowed for 7-21 days. Two cutaneous melanomas were also tested for comparison. All survival curves were analysed using the Linear Quadratic (LQ) model. Specific parameters for the intrinsic radiosensitivity (α-component, SF2 –value), for the capacity of repair of DNA damage (β-component), as well as the α/β ratio were calculated. Results: After single dose irradiation a wide range in αand β-values was obtained for both primary and metastatic uveal melanomas, which resulted in a wide range of α/β ratios. In contrast, calculations based on split dose data with which the β-component could be estimated independent of the α-component, indicated that estimates for the capacity of sublethal DNA damage repair was very similar for all cell lines. This indicated that intrinsic factors dominated the radiosensitivity of these cell lines. Split dose irradiation had little influence on the intrinsic radiosensitivity (α-component), but cell survival increased for all cell lines. For the two cutaneous melanomas comparable split dose results were obtained. Conclusions: For both primary and metastatic uveal melanoma cell lines data from single and fractionated doses do indicate large variations in radiosensitivity, which are mainly dominated by the intrinsic radiosensitivities. Doses of around 8 Gy in 5 fractions would be sufficient to eradicate 109 cells (approximately 1 cm3) of the most radioresistant tumour cell lines, but this schedule is overkill for the radiosensitive tumour cell lines. Based on specific morphological and histological tumour markers more individualised dose fractionation schedules could improve the therapeutic ratio for uveal melanomas. IOVS 2003 Nov;44(11):4660-4. Dose fractionation effects in primary and metastatic human uveal melanoma cell lines