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

<p>Abstract</p> <p>Background</p> <p>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).</p> <p>Materials and methods</p> <p>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) PTV_routine, derived from a single GTV plus 'conventional' margins; (ii) PTV_{all phases}incorporating all 3D mobility captured by the 4DCT; (iii) PTV_gating, 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.</p> <p>Results</p> <p>Individual GTVs ranged from 41.5 – 235.0 cm³. With patient-specific mobility data (PTV_{all phases}), smaller PTVs were derived than when 'standard' conventional margins were used (p < 0.001). The average residual 3D tumor mobility within the gating window was 4.0 ± 3.5 mm, which was 5.5 mm less than non-gated tumor mobility (p < 0.001). The reductions in mean lung dose were 9.7% and 4.9%, respectively, for PTV_{all phases}versus PTV_routine, and PTV_gatingversus PTV_{all phases}. The corresponding reductions in V₂₀were 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.</p> <p>Conclusion</p> <p>Respiration-gated radiotherapy can reduce the risk of pulmonary toxicity but the benefits are particularly evident for tumors of the middle and lower lobes.</p>

Abstract licence: CC BY-NC-ND

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