Implementing ocular treatment with pencil beam scanning: the FHCC experience

The Fred Hutchinson Cancer Center (FHCC) has developed a novel in-house method for ocular proton therapy by adapting a pencil beam scanning (PBS) beamline and using a commercial treatment planning system. This manuscript outlines the workflow from simulation to treatment delivery and presents our experiences with the initial 40 patients.

Key innovations of our treatment approach include in-house developed treatment chair and gaze localization systems, CT imaging for planning, and a Monte Carlo algorithm for dose calculation. We gathered data on patient characteristics, dose volume statistics, and total treatment time. Additionally, we examined the distances patients traveled to access ocular proton therapy. An example illustrating our treatment technique is also presented.

The average patient age at the time of treatment was 63.9 years. Tumor apical height ranged from 0.7 to 11.9 mm, and the largest basal diameter from 2.8 to 15.5 mm. GTV volumes ranged from 0.02 to 0.89 cc, while PTV volumes ranged from 0.17 to 2.27 cc. The D99% dose to GTV ranged from 5041 to 5242 cGy (RBE). The median mean dose to the lacrimal gland was 1570 cGy (RBE), while the median D2% doses to the optic nerve, macula, and optic disc were 4188 cGy (RBE), 5024 cGy (RBE), and 5133 cGy (RBE), respectively. Out of the 40 patients, 16 successfully met all treatment planning goals. The remaining patients did not meet some goals due to the target either abutting or being close (< 2 mm) laterally or distally to the OARs. The total treatment duration per fraction was approximately 25 min. Nearly one-third of the patients traveled around 900 miles to receive ocular treatment.

The approach at FHCC demonstrates that ocular proton therapy can be effectively delivered using a general-purpose PBS beamline, providing a solution for centers without dedicated ocular beamlines.