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Initial clinical experience with stereotactic lung radiotherapy, based on a biological model-driven prescription method
C. Wesley. Hodge, Wolfgang. A. Tomé, Tracy Weigel, Anne M. Traynor and Minesh. P. Mehta

Objective: A patient specific nomogram based biological dose selection (NBDS) model may allow for selection of a safe and effective dose schedule to treat early peripheral stage non-small cell lung cancer (NSCLC) with stereotactic body radiotherapy (SBRT). We report the initial clinical outcomes testing these concepts.

Methods: 23 patients with stage IA/B NSCLC were treated with SBRT. All patients had a prescription isodose volume/residual lung volume ratio of 2-3%, permitting a wide range of dose fractionation schemes under the NBDS-model that should yield a sufficiently low grade 2 or higher pneumonitis rate that the resultant long-term grade 3 or higher complication rate would be <20%. Based on the predications of the patient specific NBDS-model all patients could be safely treated using a modal prescription of 60 Gy in 5 fractions over 10 calendar days, with a median normalized tissue dose (NTD) of 122.4 Gy10. Kaplan-Meier analysis was performed to assess local control, overall, cause-specific and disease free survival. Toxicities and response rates were analyzed.

Results: Median follow-up was 43.2 months for all living patients. Analysis of 20 evaluable lesions demonstrated a major response rate of 80%. 3 year actuarial overall, cause-specific, and disease free survival, were 60, 79, and 55%, respectively. 3 year actuarial local control was 89%. Grade 2 or higher acute pulmonary toxicity was observed in 5 patients. The 1, 2 and 3-year actuarial incidence of grade 2 or higher pulmonary toxicity was 15, 27 and 27% (95% CI = 5 – 48%), with corresponding grade 3 incidence of 4, 10, and 10%. No grade 3 or higher non-pulmonary side-effects were observed.

Conclusion: SBRT using a biological model-based fractionation scheme yields local control and survival rates comparable to other series that treat to higher NTDs; the pulmonary toxicity rate and grades are within the model-predicted parameters, but further follow-up is necessary for long-term validity of the model.

Keywords: Lung; Cancer; Stereotactic body radiotherapy; Radiotherapy; Radiobiology

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