Purpose: This work aims to estimate uncertainties in deformable image registration (DIR) based dose accumulation (DDA) during radiotherapy of head and neck cancer (HNC). We project the confidence intervals of cumulative parotids' DVH parameters to guide adaptive radiotherapy clinical decision making.
Methods: We used the planning CTs (PCTs) of twenty HNC patients treated with tomotherapy as reference images to reconstruct and accumulate doses from daily images (MVCTs) utilizing a DIR algorithm (PreciseART, Accuray, Inc.). Uncertainties related to daily dose mapping inconsistencies were estimated by warping the planning contours to the MVCT, comparing DVHs computed in the PCT and MVCT, and deriving upper and lower dose distributions for the planning structures. We determined the overlapping percentage between the mid-treatment projected uncertainty bounds and the final uncertainty bounds of dose-volume parameters. These projections were compared with the constraint points to evaluate if plan adaptation was required.
Results: Among all cases, the average mid-treatment projections agree in magnitude with the final cumulative uncertainty bounds for the parotids mean dose, D50%, and V20Gy: 3.2%, 5.9%, and 4.5% of the planning value versus 3.5%, 6.6%, and 4.7%, respectively. The projected uncertainty intervals intersected with the final bounds in 78% of the metrics, with overlapping percentages greater than 60% for half of them. At mid-treatment, the uncertainty bounds of the metrics of five patients were projected to exceed the constraint point by at least 3%; this threshold was exceeded at the end of treatment for the five cases.
Conclusion: DDA-related uncertainty bounds for cumulative dose-volume parameters were estimated for parotid glands of HCN patients. We confirmed that a mid-treatment projected 3% violation on dose-volume constraints leads to the same or higher violation at the treatment end. Approximately one-fourth of patients are expected to require mid-treatment replanning for parotids sparing based on a 3% threshold.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by the MCW Fotsch Foundation and by Manyeia Med
Deformation, Image Guidance, Tomotherapy
TH- External Beam- Photons: Dose reconstruction over deforming anatomies