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A Decade of “50 in 5”: Maturing SBRT Outcomes for Medically Inoperable Early-Stage Lung Cancer at a Single Institution Over 10 Years

Early-Stage Non-Small Cell Lung Cancer

      Purpose/Objective(s)

      To report on 10 years of experience with the first lung stereotactic body radiation therapy (SBRT) fractionation schedule used from the initiation of our institutional SBRT program.

      Materials/Methods

      We surveyed our IRB-approved prospective SBRT registry for all medically inoperable non-small cell lung cancer patients treated with 50 Gy in 5 fractions between 10/1/2003 and 12/31/2012. All patients were treated on stereotactic-specific LINAC with vacuum-bag based for immobilization and abdominal compression to limit tumor motion. Under compression, CT simulation images of tumor acquired at rest, full inhalation, and full exhalation were merged to generate an internal target volume (ITV). Dose was prescribed to cover ≥95% of the planning target volume (PTV) defined as PTV=ITV + 5 mm margin. SBRT was planned using heterogeneity corrections and delivered by 7-9 IMRT beams over consecutive days with daily infrared-based x-ray positioning system for IGRT.

      Results

      Three hundred forty lesions were treated in 300 patients, of which 15% had multiple treatments. Median follow up for survival was 17.4 months (range 0.3-112.2) and 17.8 months for living patients (range 2.1-96.7) with 46.7% of patients alive at analysis. Median age was 74 years (range 37-97); median KPS was 80 (range 40-100); 56% were female. Median FEV1 and DLCO (as % predicted) were 59 and 52. The principal co-morbidity for medical inoperability was pulmonary in 62.0% of patients, with 18.3% smoking at SBRT. Median tumor diameter was 2.4 cm (range 0.1-10); median PET SUV max was 7.6 (range 1-59); 36.2% of tumors had no or non-diagnostic biopsies. Per RTOG 0813 definition, 115 lesions (33.8%) were “central.” Overall, the rate of any grade toxicity was 13.0 % (with no grades 4 or 5) and chest wall symptoms constituted 7.7%. For central versus non-central lesions, the toxicity rate was 15.5% vs 11.7%, with chest wall toxicity constituting 5.8% vs 8.6% and pneumonitis 5.8% vs 3.0%, respectively. For central versus non-central lesions, 5-year actuarial local control, distant metastases-free, disease failure-free, and overall survivals (in %) were 79.0 vs 75.4, 49.5 vs 56.7, 37.2 vs 34.3, and 18.3 vs 20.3, respectively. At analysis, crude rates by lesion of local, lobar and regional nodal failure (in %) were 11.2, 4.1 and 13.5, respectively. There were no statistically significant differences in the failure rates between central and non-central lesions for all parameters.

      Conclusions

      A decade’s experience with Lung SBRT using 50 Gy in 5 fractions reveals excellent local control. Patterns of cancer failure are mainly distant. Co-morbidities drive mortality in this population. This schedule is effective independent of tumor location in the lung, with minimal toxicities that are location-dependent.

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