A dosimetric analysis of respiration-gated radiotherapy in patients with stage III lung cancer

Abstract

Abstract Background Respiration-gated radiotherapy can permit the irradiation of smaller target volumes. 4DCT scans performed for routine treatment were retrospectively analyzed to establish the benefits of gating in stage III non-small cell lung cancer (NSCLC). Materials and methods Gross tumor volumes (GTVs) were contoured in all 10 respiratory phases of a 4DCT scan in 15 patients with stage III NSCLC. Treatment planning was performed using different planning target volumes (PTVs), namely: (i) PTVroutine, derived from a single GTV plus 'conventional' margins; (ii) PTVall phases incorporating all 3D mobility captured by the 4DCT; (iii) PTVgating, incorporating residual 3D mobility in 3–4 phases at end-expiration. Mixed effect models were constructed in order to estimate the reductions in risk of lung toxicity for the different PTVs. Results Individual GTVs ranged from 41.5 – 235.0 cm3. With patient-specific mobility data (PTVall phases), smaller PTVs were derived than when 'standard' conventional margins were used (p all phases versus PTVroutine, and PTVgating versus PTVall phases. The corresponding reductions in V20 were 9.8% and 7.0%, respectively. Dosimetric gains were smaller for primary tumors of the upper lobe versus other locations (p = 0.02). Respiratory gating also reduced the risks of radiation-induced esophagitis. Conclusion Respiration-gated radiotherapy can reduce the risk of pulmonary toxicity but the benefits are particularly evident for tumors of the middle and lower lobes.