Purpose: To evaluate a novel respiratory motion compensation strategy combining gated beam delivery with the mean target position (MTP) concept for pulmonary stereotactic body radiotherapy (SBRT).

Materials And Methods: Four motion compensation strategies were compared for 10 targets with motion amplitudes between 6mm and 31mm: the internal target volume concept (plan(ITV)); the MTP concept where safety margins were adapted based on 4D dose accumulation (plan(MTP)); gated beam delivery without margins for motion compensation (plan(gated)); a novel approach combining gating and the MTP concept (plan(gated&MTP)).

Results: For 5/10 targets with an average motion amplitude of 9mm, the differences in the mean lung dose (MLD) between plan(gated) and plan(MTP) were <10%. For the other 5/10 targets with an average motion amplitude of 19mm, gating with duty cycles between 87.5% and 75% reduced the residual target motion to 12mm on average and 2mm safety margins were sufficient for dosimetric compensation of this residual motion in plan(gated&MTP). Despite significantly shorter duty cycles, plan(gated) reduced the MLD by <10% compared to plan(gated&MTP). The MLD was increased by 18% in plan(MTP) compared to that of plan(gated&MTP).

Conclusions: For pulmonary targets with motion amplitudes >10-15mm, the combination of gating and the MTP concept allowed small safety margins with simultaneous long duty cycles.

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http://dx.doi.org/10.1016/j.radonc.2011.01.008DOI Listing

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