Lung Cancer

PV QA 4 - Poster Viewing Q&A 4

TU_29_3609 - Radiation to the Immune System May be an Important Risk Factor for Long-term Survival After SBRT in Early Stage Non-small Cell Lung Cancer: a Role of RT Plan Optimization

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

Radiation to the Immune System May be an Important Risk Factor for Long-term Survival After SBRT in Early Stage Non-small Cell Lung Cancer: a Role of RT Plan Optimization
F. M. Kong1, H. Zhang2, Y. LIU3, H. Yao2, A. Cerra-Franco2, K. Shiue2, D. Vile2, W. Wang2, M. P. Langer2, G. Watson2, G. Bartlett2, K. Diab4, T. Birdas5, R. D. Timmerman6, T. Lautenschlaeger2, and J. Y. Jin2; 1Indiana University Radiation Oncology, Indianapolis, IN, 2Department of Radiation Oncology, Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN, 3Department of Thoracic Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, China, 4Indiana University School of Medicine, Indianapolis, IN, 5Department of Surgery, Indiana University school of medicine, Indianapolis, IN, 6Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX

Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) is the treatment of choice in patients with early stage inoperable non-small cell lung cancer (NSCLC). Local tumor control after SBRT is outstanding; however, 5-year overall survival rates remain suboptimal at less than 50%, which cannot be fully explained by known etiologies such as comorbidity, distant cancer progression or conventional toxicity. We hypothesize that radiation to normal tissue, particularly the sensitive lymphocytes in the immune system, contribute to the poor survival in these patients.

Materials/Methods: Patients with T1-T2 N0 M0 NSCLC who received SBRT without previous RT and had retrievable radiotherapy (RT) plans in our modern treatment planning system were eligible. The primary endpoint was overall survival, calculated from the start of SBRT. Clinical factors included age, gender, race, tobacco history, respiratory and cardiovascular comorbidity, tumor lobar location, histology, T stage, gross tumor volume (GTV), planning target volume (PTV), and prescription dose BED10. Heart and lung were contoured consistently by one radiation oncologist according to the RTOG atlas. Effective dose to lymphocytes were computed by an in-house model.

Results: A total of 280 patients met criteria. The median follow-up was 6.7 years. The median survival time was 33 months (95% CI: 25-42 months). The 2-year, 3-year and 5-year survival rates were 63%, 53% and 45%, respectively. Univariate analysis demonstrated that age (HR=1.02, p=0.04), gender (HR=0.75 for female, p=0.07), tumor T stage (HR=1.3 for T2, 2.5 for T3, using T1 as the reference, p=0.10), KPS(HR=0.97, p<0.001), GTV (HR=1.01, p<0.001), PTV (HR=1.01, p<0.001), mean lung dose (HR=1.2, p<0.001), mean heart dose (HR=1.001, p=0.029) and EDIC were all significantly associated with overall survival. Multivariate analysis demonstrated KPS, GTV, mean lung dose, mean heart dose and EDIC were all significant as continuous variables, but only KPS, GTV, EDIC remained. A 1 Gy increase in EDIC was associated with a 46 % increase in the risk of death, or 20% reduction in 5-year survival.

Conclusion: This study is the first to demonstrate that radiation dose to lung, heart and lymphocytes are independent factors predicting long-term overall survival after SBRT. These findings suggests that the poor survival after SBRT is likely at least in part from damage to radiation-sensitive lymphocytes and may suggest an area of further plan optimization during SBRT practice.

Author Disclosure: F.(. Kong: Research Grant; Varian, NCI/NIH. Founding President and Board of Director; Sino-American Network for Therapeutic Radiation On. President 2015; American Association of Women Radiologists (AAWR). President 2012-2013; Association for Chinese Professors. Founding Board Member; Sino-American Network for Therapeutic Radiology. H. Zhang: None. Y. LIU: None. A. Cerra-Franco: None. D. Vile: None. M.P. Langer: None. G. Watson: None. R.D. Timmerman: Research Grant; Varian Medical Systems, Accuray, Inc, Elekta Oncology. T. Lautenschlaeger: None. J. Jin: Employee; Indiana University Health. Research Grant; Varian medical system, Xstrahl Inc. Honoraria; Varian medical system. Board memebr; SANTRO.

Feng-Ming Kong, MD, PhD, FACR, FASTRO

Indiana University School of Medicine

Disclosure:
Employment
University of Michigan: Adjunct Faculty: Employee

Compensation
NCI/NIH: Research Grants; Varian: Research Grants

Leadership
American Association of Women Radiologists (AAWR): President 2015; Association for Chinese Professors: President 2012-2013; Sino-American Network for Therapeutic Radiation On: Founding President and Board of Director; Sino-American Network for Therapeutic Radiology: Founding Board Member

Presentation(s):

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TU_29_3609 - Radiation to the Immune System May be an Important Risk Factor for Long-term Survival After SBRT in Early Stage Non-small Cell Lung Cancer: a Role of RT Plan Optimization



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