Stereotactic body radiotherapy for central lung tumors

Patients with centrally located lung tumors have been reported to have a higher risk of toxicity when treated with stereotactic body radiotherapy (SBRT) compared with patients with peripheral tumors. The optimal SBRT fractionation schedule for treatment of central tumors is unknown. The primary purpose of this study was to assess toxicity in patients with central lesions treated with SBRT at our institution, the majority of whom were treated with four fractions.

Forty-seven patients with 51 central lesions, either primary lung cancer or lung metastases, were treated with SBRT at the Department of Therapeutic Radiology, Yale University School of Medicine/Yale Cancer Center from 2007 to 2011. The patients were treated with three to five fractions with the majority of patients receiving 50 Gy in four fractions of 12.5 Gy. Forty of the lesions were located within 2 cm of the proximal tracheobronchial tree whereas 11 were located within 2 cm of other mediastinal structures. Toxicity data were collected and analyzed according to pretreatment and tumor characteristics and dosimetric parameters. Lobar control data were compiled.

With a median follow-up of 11.3 months (range, 4.8-40.8), four patients experienced grade 3 dyspnea and one patient developed hemoptysis that contributed to respiratory failure and subsequent death. Grade 2 toxicity included fatigue (n = 3), dyspnea (n = 3), chest-wall pain (n = 1), and cough (n = 1). Patients with grade 3+ toxicity had larger maximum tumor diameters compared with those patients without grade 3+ toxicity (median diameter 4.3 cm versus 2.9 cm, p = 0.02). There were no detectable significant differences between the two groups with respect to baseline pulmonary function tests, distance to tracheobronchial tree, maximum point dose to the tracheobronchial tree, maximum dose to 5 cc of the tracheobronchial tree, mean lung dose, and volume of lung receiving 5 Gy, 10 Gy, and 20 Gy. There were two patients who experienced local recurrences. The median biological equivalent dose (linear quadratic formula, α/β = 10) for patients with local recurrence was 76 Gy compared with 112.5 Gy for patients without local recurrence (2-tailed t test, p = 0.04). The 2-year actuarial lobar local control for the entire cohort was 94%. The 2-year lobar local-control rate for patients receiving a biological equivalent dose of 100 Gy or more was 100% and for those receiving less than 100 Gy was 80% (log rank, p = 0.02).

SBRT for central lung tumors seems to be safe, although treatment of larger tumors does carry an increased risk of high-grade toxicity. Efforts to decrease the toxicity risk by decreasing the biologically equivalent dose resulted in increased local failure.