ESTRO 2024 - Abstract Book

S4349

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

Proton therapy is employed worldwide to treat ocular malignancies, utilizing a diverse set of delivery systems. The emergence of new treatment centers with non-dedicated systems is introducing further diversity of dose characteristics between treatment facilities. However, the 2.5 mm lateral margin remains a widely adopted standard across these centers. This study quantifies the lateral margin requirement in relation to dose field characteristics to ensure comparable target coverage across various facilities.

Material/Methods:

In this study, we investigate acceptable deviations to the intended clinical eye orientation by assessing target coverage resulting from deviations from the planned orientation for a cohort of 16 patients. Using a point cloud model of the eye, we applied translations and measured translation-induced rotations to identify the three-dimensional boundary conditions which ensures adequate target coverage. The translation-induced rotations are derived from our analysis of measured intra-fractional motion using our in-house eye tracking system, suggesting a patient-specific correlation between introduced translation and eye rotation. The 3D boundary was first defined based on the dose characteristics of the OPTIS2 treatment room at the Center for Proton Therapy, Paul Scherrer Institute in Switzerland. Subsequently, the simulation was extended to a range of lateral margins and dose penumbras reported from operational treatment facilities around the world.

Results:

Figure 1 depicts our analysis which identifies a range of offsets for the investigated cohort within which target coverage is preserved for the considered lateral margins and penumbras. Results obtained with our facility's beam characteristics reveal that target coverage for all examined patients would remain uncompromised for deviations from the planned orientation within 0.59 mm, 0.64 mm, and 1.62 mm along the x, y, and z axes of the treatment room. In contrast, the median representation across the entire patient cohort exhibited values of 1.09, 1.09, and 3.16 mm in the x, y, and z dimensions, respectively. The correspondence between the ranges illustrated in figure 2 suggest that comparable offset tolerance for a given treatment facility can be approximated with the equation: Lateral margin = 0.761*penumbra + 1.228 mm.