Dose-guided radiotherapy: potential benefit of online dose recalculation for stereotactic lung irradiation in patients with non-small-cell lung cancer

Purpose: To determine whether dose-guided radiotherapy (i.e., online recalculation and evaluation of the actual dose distribution) can improve decision making for lung cancer patients treated with stereotactic body radiotherapy.

Methods and materials: For this study 108 cone-beam computed tomography (CBCT) scans of 10 non-small-cell lung cancer patients treated with stereotactic body radiotherapy were analyzed retrospectively. The treatment plans were recalculated on the CBCT scans. The V(100%) of the internal target volume (ITV) and D(max) of the organs at risk (OARs) were analyzed. Results from the recalculated data were compared with dose estimates for target and OARs by superposition of the originally planned dose distribution on CBCT geometry (i.e., the original dose distribution was assumed to be spatially invariant).

Results: Before position correction was applied the V(100%) of the ITV was 100% in 65% of the cases when an ITV-PTV margin of 5 mm was used and 52% of the cases when a margin of 3 mm was used. After position correction, the difference of D(max) in the OARs with respect to the treatment plan was within 5% in the majority of the cases. When the dose was not recalculated but estimated assuming an invariant dose distribution, clinically relevant errors occurred in both the ITV and the OARs.

Conclusion: Dose-guided radiotherapy can be used to determine the actual dose in OARs when the target has moved with respect to the OARs. When the workflow is optimized for speed, it can be used to prevent unnecessary position corrections. Estimating the dose by assuming an invariant dose instead of recalculation of the dose gives clinically relevant errors.