Salvage Re-Irradiation with Stereotactic Radiotherapy for In-Field Neck Lymph Node Recurrence: A Retrospective Study

Abstract

Neck lymph node (LN) recurrence in the irradiated field is an important characteristic of treatment failure after primary radiotherapy owing to the lack of standard treatment. Recent technological advances have led to the possibility of achieving highly conformal dose distributions of recurrent tumors using stereotactic radiotherapy (SRT), resulting in high local control (LC) and low toxicity, with reduced dose to organs at risk (OAR). We aimed to investigate the efficacy and safety of SRT for neck LN recurrence after radiotherapy. Between 2008 and 2016, 58 neck LN recurrences after radiotherapy in 18 patients with head and neck cancer were treated using a treatment system specialized for stereotactic irradiation. The nasopharynx (17 lesions), oropharynx (4 lesions), hypopharynx (7 lesions), buccal mucosal (13 lesions), tongue (2 lesions), and larynx (15 lesions) were the primary tumor sites. No patient exhibited recurrences at the primary sites during SRT. The target marginal dose (18–20 Gy) was administered in one fraction. Treatment doses and fractions were determined according to the tumor volume and OAR. If the dose for 10 cm3 of the skin or mucosa exceeded 14 Gy in one fraction because of large tumor volume or if the target area was in close proximity to OAR, the number of fractions was increased to prevent adverse effects, e.g., skin ulcers. Diagnostic imaging techniques, such as CT, MRI, and FDG-PET/CT, were used to evaluate tumor response every 2–3 months after SRT. Kaplan–Meier method was used to calculate overall survival (OS) and LC rates, and log-rank test was used to compare 1-year LC differences as per LN volume. The median follow-up period and target volume was 16 (range, 1–80) months and 1.3 (range, 0.05–91) cm3, respectively. The median previous radiotherapy dose and marginal dose of SRT as equivalent dose delivered in 2-Gy fractions (α/β = 10) was 66 (range, 40–70) Gy and 50 (range, 40–58) Gy, respectively. Moreover, the median interval between completion of prior radiotherapy and SRT was 23.5 (range, 4–69) months and 1-year LC and OS rates were 81% and 61%, respectively. Local recurrence was observed in 12 lesions from nine patients. LC was higher with a target volume ≤ 1.0 cm3 than with a target volume > 1.0 cm3 (p = 0.016). The 1-year LC was higher with a target volume ≤ 1.0 cm3 than with a target volume > 1.0 cm3 (92% vs. 68%, respectively). No significant difference in LC was observed when considering other clinical factors. Regarding the cutaneous region and mucosa, grade ≥3 adverse effects were not observed. One patient with large (91 cm3) and widespread tumor that metastasized the carotid artery before SRT showed fatal bleeding. SRT for neck LN recurrence is safe and feasible in most cases, but the treatment indication should be carefully considered for large and widespread tumors.