Some factors of importance in the radiation treatment of malignant melanoma.

The results of radiotherapy in 204 lesions of malignant melanoma in 114 patients were analysed with regard to radiobiological parameters such as total dose, dose per fraction, treatment time, tumour volume and also by various fractionation models. Ninety-seven of 204 lesions showed a complete response (CR) which was persistent in 80. Neither total dose, treatment time nor various modifications of the nominal standard dose (NSD) concept showed any well-defined correlation with response. There was, however, a significant relationship between dose per fraction and response so that high doses per fraction yielded a significantly better response (24% CR for doses less than 4 Gy vs. 57% CR for doses greater than or equal to 4 Gy, p less than 0.001). The lack of influence of treatment time influence allowed an analysis of the data according to the linear-quadratic model yielding an alpha/beta ratio of 2.5 Gy. Using this ratio, an iso-effect for different fractionation schedules could be estimated by the extrapolated total dose (ETD). This was further improved when corrected for the other important parameter which was tumour volume. Thus, an iso-effect formular for malignant melanomas could be calculated as ETDvol = D X ((d + 2.5)/2.5) X M-0.33 where d is total dose and dose per fraction in Gy, respectively and M is mean diameter (cm). The 50% response for ETDvol was found to be 86 Gy. This formular seems to be currently the best way to determine an optimal radiation schedule for effective radiation treatment of malignant melanoma. Treatment of 45 patients with only local or regional disease showed 26 patients who achieved local tumour control with a 56% 3-year survival compared to no survivors among 19 patients in whom the disease could not be controlled locally. This indicated that proper attention should be given to the local treatment of recurrent melanoma since this has important implications for survival. Successful treatment of malignant melanoma may be possible when the special radiobiological features of the disease are taken into account.