Importance of tumor size and repopulation for radiocurability of skin cancer.

Data on 946 skin cancers treated by radiation were used to estimate the importance of repopulation. Six different treatment regimes were used from a single dose to 74 Gy given in 47 fractions. High local control of the small skin cancers (L 1 cm) was independent of dose fractionation. For large tumors, only 74 Gy in 47 fractions was the optimal treatment. Time factor analysis showed a steep increase in the NTD50 values between day 28 and 65 of treatment. This implies that tumor clonogen repopulation starts around 4 weeks of treatment. The present results showed a three-component dose response curve instead of the two-component curves which were found for head and neck and bladder cancer.