Purpose/ObjectiveSuperior sulcus tumors are frequently treated with neoadjuvant chemoradiotherapy (nCRT) followed by surgery in a trimodal approach. The INKA study evaluated the replacement of photon irradiation by carbon ion radiotherapy (C12-RT) in this regimen. Material/methodsThe prospective INKA-study included patients with locally advanced non-small cell superior sulcus tumors (<cN3 cM0). Patients received 2 cycles of cisplatin and vinorelbine as per local standard. During the second cycle, 39Gy(RBE) of hypofractionated C12-RT in 13 fractions were applied. Surgery following an FDG-PET/CT restaging was performed 2 weeks later. The primary endpoint was feasibility and safety measured by the incidence of CTCAE (v4.0) grade 3/4 toxicity and/or discontinuation due to any reason. Secondary endpoints included the morphological (RECIST 1.0), metabolic (PERCIST 1.0) and histopathological response after nCRT as well as Quality of Life measurement (QLQ-C30/LC13). ResultsBetween 2015 and 2020, 14 patients were included and received nCRT. No grade 3/4 toxicity occurred with no discontinuation due to toxicity. Before surgery, 8 patients (57%) showed a partial response on CT scan. Thirteen patients showed a metabolic response (mCR=1, mPR=12). Three patients were judged as inoperable after nCRT (21%). In patients with resection, a pathological CR was seen in 2 patients (19%) and near-complete remission (<10% vital tumor cells) in 6 patients (55%). Pain score was more than halved compared to baseline (mean: 69.2±26.2 vs. 30.6 ± 29.1; p=0.005) after completion of nCRT and before surgery. ConclusionThe INKA trial is the first study to evaluate nCRT with C12-RT and showed excellent response, low toxicity and rapid pain relief.