Author: Amanda J. Deisher, Susannah V. Hickling, Shima Ito, Jon J. Kruse 👨🔬
Affiliation: CancerCare Manitoba, Mayo Clinic 🌍
Purpose:
To date, 11 ocular patients were treated with spot scanning gantry-based gaze-gated ocular proton program at Mayo Clinic, Rochester MN since 2023. Treatments are done in the half-arc gantry room utilizing robotic couch and 2D kV imaging. Three major new components to the program include a mechanical aperture mount which inserts into gantry nozzle and holds a 3D-printed patient specific aperture, a table-mounted gaze-monitoring hardware with a moveable camera, and gaze-gating software which calculates center of pupil and sends gate when the pupil is within the gate.
In this abstract, we focus on treatment planning process for the ocular proton treatment.
Methods:
Target contouring and aperture design were done with Eclipse (Varian Medical Systems); initiated by MD contouring the target and OAR based on CT/MR fusions; followed by a Physicist designing an aperture from a target and adding margins (1-2mm) to create a structure called “cutout”. This cutout structure is then cropped from a 6.7-cm thickness aperture placed 5.7-cm anterior to the eye’s surface. We generated a “base plan” from an anterior beam and 45-mm range shifter (RS45) with a single energy layer.
MATLAB Optimization script was then used to create DICOM plan containing spot list with spot weights. User input to the script included proximal/distal treatment depth and spot configuration (1 or 5). The spot list along with anatomical structures and aperture are exported to our in-house GPU Monte Carlo dose calculation cluster. Dose distribution was imported back into eclipse for MD review and necessary dose normalization to ensure target coverage was made.
Results:
Prescription doses ranged from 50-60Gy in 4-5fx treated daily. Planning goal was to cover target with 100% of prescription dose while minimizing dose to anterior segment.
Conclusion:
Clinical plans and dose profiles will be presented and discuss clinical challenges we experienced during planning.