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

To evaluate the dosimetric consequences for irradiated lung tissue for different respiration conditions for hypofractionated stereotactic body radiotherapy (SBRT).

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 > or=12, 15> or= and > or=18 Gy, mean lung dose (D(mean)), NTCP corrected for fractionation effects and the total monitor units (MU) were evaluated.

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.

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.