Comparative Evaluation of Four Stereotactic Radiosurgery Planning Approaches for Treatment of Posterior Choroidal Melanoma.

INTRODUCTION

This was a comparative treatment planning study for posterior choroidal melanoma (CM) using four stereotactic approaches: Brainlab iPlan dynamic conformal arc therapy (DCAT), Brainlab Elements modulated arcs (BE), Varian Eclipse HyperArc modulated arcs (HA) and Gamma Knife ICON Leksell GammaPlan (GK). The clinical goal was to reduce dose to normal brain whilst maintaining other treatment planning goals.

METHODS

Thirteen CM cases over 3 years (2015-2018) treated with DCAT prescribed 50 Gy in 5 fractions were selected. The DCAT technique involved a forward planning method whereas semi-automated methods were used in BE, HA and GK. Target coverage and dose to critical organs were evaluated and compared across all approaches with the same set of structures used for each.

RESULTS

Volume of brain receiving 10 Gy was DCAT 0.93 cc and 0.00 cc for GK, BE, HA (p < 0.001). Brain Dnear-max GK 5.52 Gy, HA 6.41 Gy, BE 7.28 Gy, DCAT 13.73 Gy (p = 0.001). The median Gradient Index (GI) was GK 2.79, DCAT 6.39, BE 5.07, HA 6.00 (p < 0.001) with GK significantly different from each of the other approaches for PTV parameters. Further statistical significance was recorded for the lacrimal gland, contralateral lens and ipsilateral optic nerves.

CONCLUSIONS

Modulation tools in HA and BE enabled clinically meaningful reduction in dose to brain compared with DCAT whilst maintaining dose to PTV. GK produced highest PTV coverage with superior gradient index, however current methods for eye immobilisation and treatment delivery only allow for single fraction treatment with GK.