(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Adaptive radiotherapy can have a large impact in sites such as HN cancer, where anatomy changes quickly. However, its implementation may be challenging with limited resources. Many procedures deform dose to the CBCT or calculate it on a deformed CT truncated to the CBCT FOV; dose deformation and incomplete anatomy may result in inaccurate estimates. This study presents a method to calculate dose-of-the-day using all relevant anatomy, without re-simulation, and using an open-source DIR algorithm.
Methods: 15 HN patients with three CBCTs and one planning CT (pCT) each were used for this study. CBCTs were resampled and padded with air to resemble the pCT’s voxel and image array size. The pCT was rigidly aligned to the resampled CBCT and deformed using an open-source DIR algorithm; a cylindrical mask matching the CBCT FOV was created to indicate the registration volume. Metrics for registration were mutual information and a bending energy penalty term to constrain the deformation. The Jacobian was assessed to ensure a physically possible deformation, and deformed CTs (dCTs) were visually inspected for similarity to the CBCT. The dCTs were added back to the treatment planning system, where the original treatment plan was recalculated on the dCT. Contour deformation was not performed.
Results: The DIR methods were successful for all patients, resulting in images with similar anatomical coverage and HU values to the pCT while reflecting the anatomical changes for that fraction. Dose could be calculated on the resulting dCT, and the resulting dose distribution demonstrated differences between the planned dose and the delivered dose. The process took <1hr per CBCT. Although DVH parameters were not available, qualitative changes on the dose distribution could be visually inspected using isodose lines and maximum dose values.
Conclusion: This method can be used to perform dose-of-the-day calculations without requiring additional software licensing.
Keywords
Not Applicable / None Entered.
Taxonomy
IM/TH- Image Registration: Multi-modality registration
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