A method for treating a tumor, comprising identifying a tumor as a melanoma tumor and implanting in the tumor identified as a melanoma tumor, at least one diffusing alpha-emitter radiation therapy (DaRT) source (21) with a suitable radon release rate and for a given duration, such that the source (21) provides during the given duration a cumulated activity of released radon between 3.2 Mega becquerel (MBq) hour and 7.5 MBq hour, per centimeter length.