Purpose: A subset of patients treated with curative-intent stereotactic radiotherapy (RT) for limited metastases (defined as five lesions or fewer) develop local failure and/or a small number of new lesions. We hypothesized that these patients would remain amenable to curative-intent treatment with additional RT courses.
Methods and materials: Of 121 prospective patients with five lesions or fewer treated with stereotactic RT, 32 underwent additional RT courses for local failure (n = 9) and/or new lesions (n = 29). Ten patients underwent three or more courses of RT.
Results: The treated local failures developed a median of 20 months after RT completion. For the new oligometastases, the interval between the first and second RT course was 1-71 months (median, 8). Of the 32 patients undergoing multiple courses of curative-intent RT, the 2-year overall survival and progression-free survival rate was 65% and 54%, respectively. The corresponding 4-year rates were 33% and 28%. Compared with the 89 patients who underwent one RT course, these patients experienced a trend toward improved overall survival (median, 32 vs. 21 months, p = 0.13) and significantly greater progression-free survival (median, 28 vs. 9 months, p = 0.008).
Conclusion: The results of our study have shown that patients fare well with respect to survival and disease control with aggressive RT for limited metastases, even after local failure and/or the development of new metastases. Although patients amenable to multiple courses of curative-intent RT are arguably selected for more indolent disease, our hypothesis-generating analysis supports the notion of aggressively treating limited metastases, which, in some patients, might be curable and/or represent a chronic disease state.