Lung Cancer

PV QA 4 - Poster Viewing Q&A 4

TU_33_3641 - Radiologic Quantification and Predictors of Lung Fibrosis After Stereotactic Ablative Radiation Therapy(SABR)

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

Radiologic Quantification and Predictors of Lung Fibrosis After Stereotactic Ablative Radiation Therapy(SABR)
J. B. Ross, E. Schueler, R. Ko, K. Bush, P. G. Maxim, M. F. Gensheimer, B. W. Loo Jr, and M. Diehn; Stanford Cancer Institute, Stanford, CA

Purpose/Objective(s): Stereotactic ablative radiotherapy (SABR) to lung cancer lesions may result in acute or chronic fibrotic changes to lung parenchyma. These changes exist along a continuum ranging from mild scarring to marked inflammatory responses. Systematic methods to quantity SABR-induced lung fibrosis may assist in the evaluation of radiation related lung toxicity. We sought to develop a method to radiologically quantify SABR-induced lung fibrosis and conducted an exploratory analysis to identify pre-treatment radiologic features associated with fibrotic change.

Materials/Methods: We evaluated 30 patients with non-small cell lung cancer (NSCLC) treated with lung SABR using 25Gy in 1 fraction from 2012-2017. All patients had a baseline inspiratory breath hold simulation CT scan. GTV was recorded. Peri-tumor region was defined as a 2cm expansion around, but not including, GTV, respecting the lung borders and excluding large vessels and mediastinal structures. Mean and standard deviation (STD) HU and the percentage of values below -950HU (B950) for baseline ipsilateral lung and peri-tumor region were calculated. All 30 patients had a follow up scan 2-4 months post-treatment. Twenty-eight patients had a follow up scan 5-9 months post-treatment. For subjective assessment of lung fibrosis, tumor-adjacent regions were assigned a severity score of 0-4, based on a published method (Dahele et al., J Thorac Oncol 2011). For quantification of lung fibrosis, the region of fibrotic change (RFC) was determined by contouring fibrotic regions within the vicinity of the treated lesion and measuring the volume exceeding -135HU.

Results: Higher subjective fibrosis scores were associated with higher quantitative measurements of fibrosis. Mean RFC of the patient cohort increase from 2.98cc to 5.37cc from 1st to 2nd follow up scan (p=0.0854). GTV was positively correlated with RFC on 2nd follow up scan (R2=0.465, p=<0.0001). Higher GTV was associated with higher subjective fibrosis scores on 2nd follow up scan. Baseline peri-tumor mean and STD HU were positively correlated with RFC on 2nd follow up scan (R2=0.1582, p=0.0361; R2=0.1826, p=0.0233). Lower baseline peri-tumor mean and STD HU were associated with lower subjective fibrosis scores on 2nd follow up scan. Baseline ipsilateral lung mean and STD HU and ipsilateral lung B950 and peri-tumor B950 were not significantly correlated with RFC on follow up scans.

Conclusion: Radiologic quantification of lung fibrosis is an effective method to evaluate SABR-induced changes and may enable more rapid and systematic assessment compared to subjective scoring. GTV and baseline peri-tumor mean and STD HU positively correlate with radiologic lung fibrosis post-SABR. These pre-treatment radiologic features may serve as predictive imaging biomarkers of SABR-induced lung injury if validated in larger prospective studies.

Author Disclosure: J.B. Ross: None. E. Schueler: None. R. Ko: None. K. Bush: None. P.G. Maxim: None. M.F. Gensheimer: None. B.W. Loo: Research Grant; RaySearch, Varian Medical Systems Inc. Stock; TibaRay, Inc. Vice-chair; National Comprehensive Cancer Network. Chair; American College of Radiology. Board Member; TibaRay, Inc. M. Diehn: Employee; Kaiser Permanente. Consultant; Roche. Stock; CiberMed.

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