Lung Cancer

PV QA 4 - Poster Viewing Q&A 4

TU_29_3607 - Interfraction Tumor Volume Change is associated with locoregional recurrence for NSCLC SBRT

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

Interfraction Tumor Volume Change is associated with locoregional recurrence for NSCLC SBRT
K. King1, S. Mayekar1, T. Beck1, J. V. Turian1, and G. Marwaha2; 1Rush University Medical Center, Chicago, IL, 2Department of Radiation Oncology, Rush University Medical Center, Chicago, IL

Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) has become a mainstay for high-risk surgical patients with non-small cell lung cancer (NSCLC). Prior studies have examined interfraction tumor volume changes, yet information about prognostic indicators still remains unknown. With the advent of kilovoltage (kv) cone beam computed tomography (CBCT) scans during the SBRT setup process, visualization of the tumor volume changes has become easier to recognize. The purpose of this study was to evaluate the role of the tumor volume change during an SBRT course on cancer recurrence.

Materials/Methods: A retrospective chart review was conducted on 129 consecutive patients from our IRB-approved lung SBRT database treated between 2014-2016. Each patient was set up under daily stereoscopic x-ray and kv CBCT guidance. A single radiation oncologist retrospectively re-contoured the tumor volume on each sequential kv CBCT image and volumetric variances were recorded both in terms of cubic centimeters (CC) and Hounsfield units (HU). A univariate and Kruskall-Wallis analysis were employed using statistical software.

Results: One hundred and twenty-nine NSCLC patients treated with definitive intent SBRT were identified. 72 (55.8%) patients were female and 57 (44.2%) were male. 26 (20.2%) continued to smoke during their treatment, 86 (66.7%) were former smokers, and 17 (13.2%) had never smoked before. 37 (28.7%) received steroids prior to each treatment while 92 (71.3%) did not. 90 (69.8%) were located peripherally while 39 (30.2%) were located centrally (by the RTOG 0813 definition). 59 (45.7%) patients received an SBRT dose of 54 Gy / 3 fractions while 69 (53.5%) received 50-60 Gy / 5 fractions. In the 3 fraction group, there was a median increase in tumor size of +17.64% CC (-52.78% to +225.75%), and +2.46% HU (-271.05% to +215.43%), between the first and third fractions; in the 5 fraction group, a median increase in tumor size of +10.40% CC (-50.00% to +112.62%) and +7.87% HU (-122.09% to +417.49%) was observed between the first and fifth fractions. Nine (7.0%) patients experienced local recurrence, 14 (10.9%) patients experienced locoregional recurrence, and 13 (10.1%) experienced distant recurrence. On Kruskall-Wallis Test, locoregional recurrence correlated with tumor volume change between first and third fractions in 3 fraction patients (HU) (P=0.0440) and between the first and fifth fractions (CC) in 5 fraction patients (P=0.0232).

Conclusion: In this study, we observed interfraction tumor size changes in patients treated with SBRT. Of the patient, tumor, and dosimetric factors analyzed; locoregional recurrence significantly correlated with interfraction tumor size change between the first and last fraction. Further lung NSCLC SBRT interfraction volumetric studies are needed to further characterize the degree of tumor volume growth and thresholds that may predict recurrence.

Author Disclosure: K. King: None. S. Mayekar: None. J.V. Turian: None.

Kevin King, MD

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