Prolonged Time of Lung Collapse Associated With Decreased Recovery of Functional Lung Following Palliative Radiotherapy

Abstract

<h3>Purpose/Objective(s)</h3> Bronchial obstruction leading to lung collapse from primary lung or metastatic tumors is a common urgent consult to radiation oncology. Palliative chest radiotherapy (RT) can reduce the risk of progression of endobronchial or extrabronchial disease can be utilized alone or in combination with bronchial stenting to re-open existing collapsed lung. The ability to re-open collapsed lung following RT is likely multi-factorial with time since lung collapse long thought as an important predictor of reversibility. In this study, we sought to quantify the time-dependency of recovery of functional lung volume in patients with partial or complete lung collapse using a CT-based imaging metric highly correlated with lung function. <h3>Materials/Methods</h3> Patients with primary lung or metastatic tumors who received palliative chest RT due to segmental, lobar or whole lung collapse who additionally had follow-up CT imaging of the chest were identified from the institutional electronic health record. Total lung volumes on simulation and follow-up chest CTs were manually segmented using a commercially available software. To evaluate functional lung volume, a subthreshold function was applied to the image sets to determine volume of lung with attenuation of -950 to -701 HU. An estimate of time since initiation of lung collapse was determined by review of clinical records and imaging. <h3>Results</h3> A total of 25 evaluable patients were identified with non-small cell lung cancer (NSCLC) being the predominant histology observed (19/25, 76%). The median time of collapse before initiation of RT was 11 days (range = 3-57). The median dose received was 20 Gy in 5 fractions (range = 8 Gy/1 fx to 30 Gy/10 fx). The mean change in total lung volume was 1090 cc with mean change in functional lung volume of 1006 cc. Overall, a 92% increase in functional lung volume was observed following chest RT in this cohort. A linear trend toward decreasing recovery of functional lung was observed with more prolonged lung collapse (<i>P</i> = 0.074). Patients with estimated time of lung collapse of ≤14 days had higher mean recovery of functional lung (113%) compared with those with lung collapse > 14 days (55%) (<i>P</i> = 0.040). <h3>Conclusion</h3> Early initiation of palliative RT following lung collapse may lead to greater recovery of functional lung volume, which may confer a survival benefit/decrease hospitalization rates/improve fitness for systemic therapy. Improvements in targeted therapies are leading to more durable systemic responses potentially increasing the importance of timely chest RT for patients with existing or pending lung collapse as a bridge during acute thoracic events.