The utility of non-axial treatment beam orientations for lower lobe lung cancers

Abstract

Purpose: Traditional treatment beams for non-small cell lung cancer are limited to the axial plane. For many tumor geometries non-axial orientations appear to reduce the dose to normal tissues (e.g. heart, liver). We hypothesize that non-axial beams provide a significant reduction in incidental irradiation of the heart and liver, while maintaining adequate target coverage. Materials and Methods: CT scans of twenty-four consecutive patients with lower lobe lung cancers were studied. For each patient, an opposed oblique axial beam pair and a competing non-axial opposed oblique pair were generated. The competing plans delivered comparable doses/margins to the GTV. DVHs and integral doses were computed for all structures of interest for the two competing plans. The integral dose was compared for axial and non-axial beams for each contoured organ using a paired t-test. Results: Dose to the heart was significantly lower for the non-axial plans (p=.0001). For 20/24 patients the integral heart dose was reduced by using non-axial beams. In those patients with tumors located in the inferior right lower lobe, a lower dose to the liver was achieved when non-axial beams were used. There were no meaningful differences in dose to the GTV, lungs, or skin between axial and non-axial beams. Conclusion: Non-axial beams can reduce the dose to the heart and liver in patients with lower lobe lung cancers. Non-axial beams may be clinically beneficial in these patients and should be considered as an option during planning.