56th SSRMP Annual Meeting

Robust dynamic-collimator trajectory radiotherapy (colli-DTRT)

30 Nov 2023, 14:30

10m

Konferenzsaal Coronado (Conference Center)

Oral Radiation Therapy Session II

Speaker

Alina Paunoiu (Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland, and Department of Biomedical Engineering, ETH Zürich, Zürich, Switzerland)

Description

Purpose: To develop robust dynamic-collimator trajectory radiotherapy (colli-DTRT), including robust dosimetrically motivated path-finding, to manage patient set-up uncertainties.
Methods: colli-DTRT plans were created for one brain (30 x 2 Gy) and one breast (16 x 2.65 Gy) clinically motivated cases. colli-DTRT paths were generated through iterative fluence map optimization (FMO) and beam angle elimination. Direct aperture optimization (DAO) was applied to the paths to obtain a deliverable plan. Standard planning target volume (PTV) plans (colli-DTRT$_{\text{PTV}}$) were optimized using a PTV extending the clinical target volume (CTV) by 3 mm (brain) and 5 mm (breast). Robust plans (colli-DTRT$_{\text{robust}}$) were optimized directly on the CTV using robust FMO during path-finding and robust DAO for final plan optimization considering 5 mm systematic shifts in all three directions. All plans were normalized to 50% of the PTV/CTV. Plan quality and robustness were evaluated by comparing dose-volume endpoints of the nominal scenario and the standard deviation (σ) of the mean over all scenarios.
Results: For the brain case, D$_{98\%}$ to the CTV was 58.0 Gy (σ = 1.1 Gy) for colli-DTRT$_{\text{PTV}}$ and 57.3 Gy (σ = 2.2 Gy) for colli-DTRT$_{\text{robust}}$. D$_{2\%}$ to the right optic nerve was 38.1 Gy (σ = 10.5 Gy) for colli-DTRT$_{\text{PTV}}$ and 32.5 Gy (σ = 6.0 Gy) for colli-DTRT$_{\text{robust}}$. For the breast case, D$_{98\%}$ to the CTV was 41.0 Gy (σ = 0.3 Gy) for colli-DTRT$_{\text{PTV}}$ and 40.6 Gy (σ = 0.3 Gy) for colli-DTRT$_{\text{robust}}$. D$_{\text{mean}}$ to the right lung was 12.2 Gy (σ = 0.9 Gy) for colli-DTRT$_{\text{PTV}}$ and 11.8 Gy (σ = 0.8 Gy) for colli-DTRT$_{\text{robust}}$.
Conclusion: Robust colli-DTRT with robust dosimetrically motivated path-finding was successfully developed, improving organs at risk sparing and robustness compared to the PTV approach for two investigated cases. However, target coverage was higher in colli-DTRT$_{\text{PTV}}$ than colli-DTRT$_{\text{robust}}$ for both cases. Robustness of target coverage was the same for the breast case but better with colli-DTRT$_{\text{PTV}}$ than colli-DTRT$_{\text{robust}}$ for the brain case.
Disclosures: Supported by SNSF grant 200021_185366 and Varian Medical Systems.