Stereotactic Body Radiation Therapy of Lung Tumors: Preliminary Experience Using Normal Tissue Complication Probability-Based Dose Limits

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Abstract
To assess the feasibility and toxicity of stereotactic body radiotherapy (SBRT) for patients with locally advanced or metastatic tumors in lung. Twenty-five tumors in 17 patients were treated. All treatments were delivered in 3 daily fractions of 9 to 15 Gy per fraction. Normal tissue complication probability (NTCP) calculations (using the Lyman model) were performed to facilitate dose prescription, and doses were prescribed with a maximum allowable NTCP risk of pneumonitis of up to 20%, not to exceed 15 Gy per fraction. Planning target volumes were designed to allow for respiratory variation in tumor location. The median dose prescribed was 35 Gy (range, 24 to 45 Gy). Twenty-three of 25 tumors remained controlled at median follow-up of 14 months. Four patients experienced grade 1–2 acute toxicity. Late toxicity developed in 2 patients who received treatment to peri-hilar tumors, including one patient in whom bronchial stenosis developed with complete occlusion and lobar atelectasis 6 months after treatment. No patient had grade 3 or 4 radiation pneumonitis. SBRT prescribed within the confines of NTCP-restricted dosing on this protocol resulted in no radiation pneumonitis. Tissues other than lung parenchyma which are unaccounted for by NTCP may be dose-limiting when performing hypofractionated SBRT in the lung.