Local treatment options for patients with in-field non-small cell lung cancer (NSCLC) recurrence following conventionally fractionated external beam radiation therapy (CF-EBRT) are limited. Stereotactic body radiation therapy (SBRT) is a promising modality to achieve reasonable local control, although toxicity remains a concern.

Patients previously treated with high-dose CF-EBRT (≥59.4 Gy, ≤3 Gy/fraction) for non-metastatic NSCLC who underwent salvage SBRT for localized ultra-central in-field recurrence were included in this analysis. Ultra-central recurrences were defined as those abutting the trachea, mainstem bronchus, or esophagus and included both parenchymal and nodal recurrences. The Kaplan-Meier method was used to estimate local control and overall survival. Durable local control was defined as ≥12 months. Toxicity was scored per the CTC-AE v4.0.

Twenty patients were treated with five-fraction robotic SBRT for ultra-central in-field recurrence following CF-EBRT. Fifty percent of recurrences were adenocarcinoma, while 35% of tumors were classified as squamous cell carcinoma. The median interval between the end of CF-EBRT and SBRT was 23.3 months (range: 2.6 - 93.6 months). The median CF-EBRT dose was 63 Gy (range: 59.4 - 75 Gy), the median SBRT dose was 35 Gy (range: 25 - 45 Gy), and the median total equivalent dose in 2 Gy fractions (EQD2) was 116 Gy (range: 91.3 - 136.7 Gy). At a median follow-up of 12 months for all patients and 37.5 months in surviving patients, the majority of patients (90%) have died. High-dose SBRT was associated with improved local control (p < .01), and the one-year overall survival and local control were 77.8% and 66.7% respectively in this sub-group. No late esophageal toxicity was noted, although a patient who received an SBRT dose of 45 Gy (total EQD2: 129.7 Gy) experienced grade 5 hemoptysis 35 months following treatment.

Although the overall prognosis for patients with in-field ultra-central NSCLC recurrences following CF-EBRT remains grim, five-fraction SBRT was well tolerated with an acceptable toxicity profile. Dose escalation above 35 Gy may offer improved local control, however caution is warranted when treating high-risk recurrences with aggressive regimens.