Background and Aims

In hypofractionated proton therapy of eye melanoma (4x15 Gy(RBE)) the eyelid should be shifted from the treatment field to avoid strong skin reactions. It is usually painful for the patient and sometimes even not possible for anatomical reasons. The aim of these studies was to demonstrate the dosimetric feasibility of spatially fractionated proton therapy (SFPT) of eye with the closed eyelid. The proton beam is formed using a mesh collimators. The potential benefit of SFPT is better regeneration of microvascular structures of the irradiated eyelid.

Methods

Within the work the mesh-grid brass collimator and the dedicated range modulator were designed to obtain uniform Spread-Out Bragg Peak (SOBP) within the target volume. The system was verified at the proton eye therapy facility at IFJ PAN. The dose depth distributions was measured using Markus ionization chamber in the water phantom. Lateral profile has been determined in PMMA slab phantom using 2-D (LiF:Mg,Cu,P) thermoluminescent foils and the ProBImS scintillator system with a CCD camera.

Results

Peak-to-Valley-Dose-Ratio (PVDR) at the region of collimator was varying between 3 to 5 but due to the proton scattering the dose distribution at the depth of the tumor (15-29 mm) was practically uniform.

Conclusions

The studies demonstrated that it is possible to form the proton beam to perform the SFTP treatment of eye melanoma through the closed eyelid.

The study was partially supported by the Horizon 2020 project INSPIRE Grant No. 730983.