Dosimetric comparison of stereotactic body radiotherapy in different respiration conditions:: A modeling study

Purpose: To evaluate the dosimetric consequences for irradiated lung tissue for different respiration conditions for hypofractionated stereotactic body radiotherapy (SBRT). Methods and materials: Thirteen patients with lung lesion undergoing SBRT treatment in shallow breathing with abdominal compression (SB + AP) underwent additional multislice CT studies in free breathing (FB), deep inspiration and expiration breath hold (DIBH, DEBH). For each patient 6 different treatment plans were designed for the various respiration conditions applying standard (7/7/10 mm), reduced (5/5/5 mm) and individual margins. The FB plan with standard margins was used as a reference. The percentage of volume of the ipsilateral lung receiving total doses >= 12, >= 15 and >= 18 Gy, mean lung dose (D-mean), NTCP corrected for fractionation effects and the total monitor units (MU) were evaluated. Results: With DIBH it was possible to reduce all lung dose parameters by about 20%. Applying reduced margins in DIBH, this reduction was even increased to about 40%. The standard technique (SB + AP) with individual margins showed similar results as DIBH with standard margins. DEBH showed some improvement over FB only when reduced margins were applied. Only for 5/13 patients NTCP values > 1% were obtained. For these patients a significant NTCP reduction was achieved with DIBH techniques. Conclusions: in SBRT shallow breathing with abdominal compression produces acceptable results concerning lung DVHs. DIBH, especially with reduced margins, showed the best lung sparing. For the clinical implementation of such a technique some form of gating is advisable. However, there are some practical limitations due to high fractional doses. (c) 2006 Elsevier Ireland Ltd. All rights reserved.