Treatment plan optimization and robustness of ¹⁰⁶Ru eye plaque brachytherapy using a novel software tool

Background and purpose: To analyze treatment plan robustness and plan optimization strategies of ¹⁰⁶Ru eye plaque brachytherapy using a novel software tool.

Materials and methods: A treatment planning software was developed that allows to calculate dose-volume metrics. Plaque misplacements were simulated and evaluated with respect to the effect on tumor coverage and dose changes in critical structures. Two treatment plan optimization approaches were analyzed: (a) reducing plaque size and (b) shifting the plaque away from organs-at-risk (OAR).

Results: Maximum tumor sizes were identified which can be covered by the prescribed dose for different robustness levels (0-2mm). For an apex height of 5mm a 1mm uncertainty yielded changes in D_2% to the lens of up to ±13Gy in anterior and ±20Gy to the optic nerve in posterior tumors. By reducing the plaque size D_mean and D_2% to lens, optic nerve and macula were decreased by >60% for most simulated cases. Similarly, by shifting the plaque away from the lens dose reductions of 15%/mm in anterior and even 30%/mm in central tumors were achieved.

Conclusion: Critical structures in the treatment of uveal melanomas with ¹⁰⁶Ru plaques can benefit from the proposed, computational treatment plan optimization.