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MA 13 - New Insights of Diagnosis and Update of Treatment (ID 674)
- Event: WCLC 2017
- Type: Mini Oral
- Track: Early Stage NSCLC
- Presentations: 1
MA 13.06 - New Risk Factors for Overall Survival After SBRT in Early Stage NSCLC: A Role of RT Plan Optimization (ID 10428)
15:45 - 17:30 | Author(s): W. Wang
Stereotactic body radiation therapy (SBRT) provides over 90% local tumor control, is a treatment of choice in patients with early stage medically inoperable non-small cell lung cancer (NSCLC). However, long-term overall survival after SBRT remain suboptimal, with 5-year rates rendering less than 50%, which cannot be fully explained by comorbidity, distant tumor progression or commonly known toxicities. We hypothesize that doses of radiation to normal lung and heart contribute to poor survival in these patients.
Patients with T1-T2 NSCLC received more than 100 Gy BED and with retrievable RT plan 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. Heart and lung were contoured consistently by one radiation oncologist according to the RTOG atlas. Dosimetric factors of the total lung were computed with biocorrection of fractionation effect.
A total of 280 patients with T1-3N0 met criteria. The median follow-up were 47 months. 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), GTV (HR=1.01, p<0.001), PTV (HR=1.01, p<0.001), mean lung dose (HR=1.2, p<0.001), V5 (HR=1.02, p=0.03), V10 (HR=1.03, p=0.01), V20 (HR=1.1, p<0.001) of total lung and mean heart dose (HR=1.001, p=0.029) were associated with survival probability. The median mean lung and heart doses were 4.1Gy (range 0.8-11.2) and 0.99 Gy (range 0.3-9.7), respectively. Presence of radiation pneumonitis was not significant (p>0.1). Multivariate analysis was not performed as the dosimetric factors were correlated with each other. Among the risk factors, lung dosimetric factors were most significant. Increase in dose or volume of lung was significantly associated with poorer overall survival. A 1 Gy increase in mean lung dose corresponded to a 12 % increase in the risk of death, or 5% reduction in 5-year survival.
This study demonstrated at the first time that doses to lung and heart are significant for overall survival after SBRT, while radiation pneumonitis was not. This suggests that the suboptimal survival after SBRT may be improved with plan optimization. This data also challenges the current practice of toxicity based normal tissue dose tolerance policy.
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