Organs at Risk Considerations for Thoracic Stereotactic Body Radiation Therapy: What Is Safe for Lung Parenchyma?

Purpose: Stereotactic body radiation therapy (SBRT) has become the standard of care for inoperable early-stage non-small cell lung cancer and is often used for recurrent lung cancer and pulmonary metastases. Radiation-induced lung toxicity (RILT), including radiation pneumonitis and pulmonary fibrosis, is a major concern for which it is important to understand dosimetric and clinical predictors. Methods and Materials: This study was undertaken through the American Association of Physicists in Medicine's Working Group on Biological Effects of Stereotactic Body Radiotherapy. Data from studies of lung SBRT published through the summer of 2016 that provided detailed information about RILT were analyzed. Results: Ninety-seven studies were ultimately considered. Definitions of the risk organ and complication endpoints as well as dose-volume information presented varied among studies. The risk of RILT, including radiation pneumonitis and pulmonary fibrosis, was reported to be associated with the size and location of the tumor. Patients with interstitial lung disease appear to be especially susceptible to severe RILT. A variety of dosimetric parameters were reported to be associated with RILT. There was no apparent threshold tolerance dose-volume level. However, most studies noted safe treatment with a rate of symptomatic RILT of <10% to 15% after lung SBRT with a mean lung dose (MLD) of the combined lungs <8 Gy in 3 to 5 fractions and the percent of total lung volume receiving more than 20 Gy (V20) <10% to 15%. Conclusions: To allow more rigorous analysis of this complication, future studies should standardize reporting by including standardized endpoint and volume definitions and providing dose-volume information for all patients, with and without RILT. (C) 2018 Elsevier Inc. All rights reserved.

Automated summary

SBRT has become the standard of care for inoperable early-stage non-small cell lung cancer, recurrent lung cancer, and pulmonary metastases. Risk of RILT, including radiation pneumonitis and pulmonary fibrosis, is associated with tumor size and location, and patients with interstitial lung disease appear to be especially susceptible. Safe treatment with a low rate of symptomatic RILT can be achieved by controlling the mean lung dose and the percentage of total lung volume receiving high radiation doses.