Tumor Control and Toxicity after SBRT for Ultracentral, Central, and Paramediastinal Lung Tumors

Abstract

Purpose: Increased rates of toxicity have been described after stereotactic body radiation therapy (SBRT) for central lung tumors within 2 cm of the proximal bronchial tree (PBT). Recent studies have defined a new class of ultracentral tumors. We report our experience treating ultracentral, central, and paramediastinal tumors with SBRT and compare toxicity, disease control, and survival rates.

Methods and materials: We reviewed the records of patients with central lung tumors treated with SBRT between September 2009 and July 2017. Tumors were classified as central if within 2 cm of the PBT, ultracentral if the planning target volume touched the PBT or esophagus, and paramediastinal if touching mediastinal pleura. Actuarial rates of grades 2+ and 3+ toxicity, local control (LC), and overall survival were assessed using the Kaplan-Meier method and compared using a log-rank test. Toxicity was scored with the Common Terminology Criteria for Adverse Events, version 4.03.

Results: We identified 68 patients with 69 central lung tumors, including 14 ultracentral, 15 paramediastinal, and 39 central tumors. Fifty-three patients were treated for early stage lung cancer and 15 for lung metastases. The prescribed dose ranged from 40 Gy to 60 Gy over 3 to 8 fractions. Most patients were treated using 5 fractions (83%), followed by 8 fractions (10%). Median follow-up was 19.7 months (range, 3.3-78.3 months). The 2-year estimates of LC (89%, 85%, and 93%, respectively; P = .72) and overall survival (76%, 73%, and 72%, respectively; P = .75) for ultracentral, central, and paramediastinal tumors were similar. Ultracentral tumors had an increased risk of grade 2+ toxicity (57.6% vs 14.2% vs 7.1%; P = .007) at 2 years. One patient with an ultracentral tumor developed grade 5 respiratory failure.

Conclusions: The oncologic outcomes after SBRT for ultracentral, central, and paramediastinal lung tumors were similar, with LC exceeding 85% at 2 years using predominantly 5-fraction schedules. Ultracentral lung tumors were associated with an increased risk of toxicity in our patient cohort. Additional studies are needed to minimize toxicity for ultracentral tumors.

Conflict of interest statement

Disclosures/Conflicts of Interest:

M. Daly: Research Funding, EMD Serono

A. Monjazeb: Research Funding, Incyte, Transgene, Genentech,

Copyright © 2018 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1:

a) Axial slices showing PTV (top) and dose distribution from a) an ultracentral lung case directly abutting the left mainstem bronchus, treated to 56 Gy in 8 fractions with a maximum point dose to the proximal bronchial tree, great vessels, esophagus, and heart of 58.4Gy, 59.6Gy, 30.0Gy, and 52.5 Gy respectively b) a central lung case with the tumor located

Figure 2:

Kaplan Meier estimates of freedom from Grade 2+ toxicities for central, paramediastinal, and ultracentral tumors in the entire cohort

Figure 3a–d:

Kaplan Meier estimates of a) local control, b) locoregional control c) distant control and d) overall survival for central, paramediastinal, and ultracentral tumors in the entire cohort

Figure 3a–d:

Kaplan Meier estimates of a) local control, b) locoregional control c) distant control and d) overall survival for central, paramediastinal, and ultracentral tumors in the entire cohort

Figure 4:

Freedom from grade 2+ toxicity stratified by central airway maximum point dose for those cases that did and did not meet the RTOG/NRG 0813 constraint of 105% of the prescription dose