Minimal benefit of respiratory-gated radiation therapy in the management of thoracic malignancy

Respiratory-gated radiotherapy (RGRT) is used in several centres around the world. However, there is continuing controversy regarding the benefit of this technique. The aims of this study are to quantify the dosimetric benefits and the potential predictive factors. Thirty-four consecutive patients were planned using the RGRT and the Free Breathing (FB) approach and compared with regard to target volume coverage and normal tissue parameters. Potential predictive factors were also evaluated. Tumour coverage was similar 94.4% versus 95.5%. Use of RGRT was not associated with a significant reduction in spinal cord, oesophagus or cardiac dosimetric parameters. However, it did reduce the lung mean dose by 1.33Gy (P<0.001) and V20 by 2.2% (P<0.001). Only superior/inferior displacement of >1cm was predictive of a >5% reduction in lung V20 parameter, and these patients all had a gross tumour volume (GTV) of <100cm3. The dosimetric benefit of applying RGRT is small when applied in an unselected population of patients. Superior/inferior displacement of >1cm for tumours with GTV less than 100cm3 may be used to select patients who may derive a >5% reduction in lung V20 parameters.