Top Line: What is the risk of bronchial stenosis after 7.5 Gy x 8 for central NSCLC?
The Study: This retrospective study from the Netherlands analyzed 51 patients with early stage NSCLC (57%) or lung metastases (43%) treated with 60 Gy in 8 fractions using SBRT. Plan objectives included 95% PTV coverage by the prescription dose with a heterogeneous maximum dose between 110% and 130% of prescription dose. When targets overlapped the proximal bronchial tree (PBT), the adjacent bronchial wall was typically limited to a D0.5cc <60 Gy. For non-overlapping targets, the adjacent bronchial wall was limited to a D0.5cc <44 Gy. Fifty-one patients with a PTV within 2cm of the PBT were included. While the median distance from PTV to PBT was 0.2cm, only 2 patients actually had targets within 1cm of the main bronchus–so, we should be careful in extrapolating these findings to ultracentral tumors. Overall, 29% developed some degree of bronchial stenosis, and median time to stenosis was 9.6 months. Most (22%) were radiographic only and the rest (8%) were grade 2 with associated dyspnea or lobar atelectasis. Notably, all stenosis events involved the lobar rather than main bronchi. When retrospectively analyzed, the average max dose to the region of bronchial stenosis was 72.7 Gy. The median maximum dose to the point of stenosis was 72.7 Gy. In addition, the mean dose to the nearest bronchial segment was significantly higher in patients who had stenosis (56Gy v 34Gy). So, this study of mostly central tumors shows that over one-third develop mostly lobar bronchial stenosis, but this is typically a radiographic finding with <10% of patients developing mild symptoms. In contrast, the HILUS trial, which gave 7Gy x 8 to ultracentral tumors within 1cm of the PBT saw a 34% rate of grade 3-5 toxicity.
TBL: A third of patients develop bronchial stenosis after 8-fraction SBRT for central lung tumors or metastases, but <10% develop grade 2 symptoms when limiting maximum dose to the bronchial wall. | Rijksen, Pract Radiat Oncol 2022