Location is everything.

Why do some patients develop pneumonitis after radiation for non-small cell lung cancer (NSCLC) despite having plans with perfectly acceptable lung dosimetry? One reason may be location. This study analyzed spatial dose distribution and radiation pneumonitis risk for 165 patients treated with VMAT (60-66 Gy in 30-33 fractions) for locally advanced NSCLC. They performed a voxel-based analysis of lung and heart dosimetry to determine which clusters of voxels had the greatest difference in dose between patients who did (22%) or did not develop grade 2+ pneumonitis. Two regions in the posterior right upper and lower lobes were identified as sites where a significantly higher mean radiation dose was seen in those with (32 Gy) versus without (15 Gy) pneumonitis. Mean dose to ipsilateral and bilateral lungs were associated with increased risk of pneumonitis. | Bourbonne, Radiother Oncol 2021