Adaptive radiotherapy in lung cancer: dosimetric benefits and clinical outcome.

OBJECTIVE Anatomical changes during radiotherapy (RT) might introduce discrepancies between planned and delivered doses. This study evaluates the need for adaptive treatment in lung cancer RT. METHODS 15 patients with non-small-cell lung cancer, undergoing radical RT with or without concurrent chemotherapy, consecutively underwent planning CT scans at baseline and after 44-46 Gy. Target volumes were delineated on both scans. Phase I delivered 44-46 Gy to the initial planning target volume (PTV). Two Phase II plans for 16-20 Gy were developed on initial and mid-treatment scans, the treatment being delivered with the mid-treatment plan. The second CT structure set was fused with the initial scan data set using dose wash. Volumetric and dosimetric changes in target volumes and critical structures were assessed. RESULTS There was significant reduction in primary gross tumour volume (34.00%; p = 0.02) and PTV (34.70%; p < 0.01) in the second scan. In Plan 2, delivering the same dose to the initial PTV would have resulted in a significantly higher dose to the lung PTV (V20, 52.18%; V5, 21.76%; mean, 23.93%), contralateral lung (mean, 29.43%), heart (V10, 81.47%; V5, 56.62%; mean, 35.21%) and spinal cord (maximum dose, 37.53%). CONCLUSION Treatment replanning can account for anatomical changes during RT and thereby enable better normal tissue sparing, while allowing radical target doses with the possibility of maximizing local control. ADVANCES IN KNOWLEDGE This study supports the sparse dosimetric data regarding the quantitative tumour volume reduction, re-emphasizing the need for adaptive replanning for minimizing normal tissue toxicity without compromising local control, and adds to the existing body of literature.