Background: The efficacy of carbon-ion radiotherapy (C-ion RT) for lymph node (LN) oligo-recurrence has only been evaluated in limited single-center studies. We aimed to investigate the benefit of C-ion RT for LN oligo-recurrence in a large multi-center study. Methods: Patients who received C-ion RT between December 1996 and December 2015 at 4 participating facilities and who met the following eligibility criteria were included: (i) histological or clinical diagnosis of LN recurrence; (ii) controlled primary lesion; (iii) no recurrence other than LN; (iv) LN recurrence involved in a single lymphatic site; and (v) age ≥ 20 years. Results: A total of 323 patients were enrolled. Median follow-up period was 34 months for surviving patients. The most common dose fractionation of C-ion RT was 48.0 Gy (relative biological effectiveness) in 12 fractions. Forty-seven patients had a history of RT at the recurrent site. The 2-year local control (LC) and overall survival (OS) rates after C-ion RT were 85% and 63%, respectively. Only 1 patient developed grade-3 toxicity. Factors such as LN diameter, histology, and history of previous RT did not correlate with LC. Smaller diameters (< 30 mm) and numbers (≤ 3) of LN metastases as well as longer disease-free intervals post-primary therapy (≥ 16 months) were associated with significantly better OS. Conclusions: C-ion RT for LN oligo-recurrence appeared to be effective and safe. C-ion RT may provide a survival benefit to patients with LN oligo-recurrence, particularly to those with few LN metastases, smaller LN diameters, and longer disease-free intervals.
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