Room: ePoster Forums
Purpose: To analyze critical structure dose distributions using I-125 brachytherapy plaques and proton plans generated with a dedicated eye beamline for ocular melanoma treatment.
Methods: Nine ocular melanoma tumor cases were treated at our institution with I-125 brachytherapy plans (prescribed to 85Gy at tumor apex delivered over 7 days) during proton cyclotron maintenance. Clinically comparable proton plans were generated for the same tumors on the 67.5 MeV eye beamline using EYEPLAN (prescribed to 56GyE in 4 daily fractions). Maximum absolute dose (Dmax) and maximum dose as a percentage of prescription (Dmax/%Rx) were extracted for optic disc (OD), macula, and lens, with the latter metric accounting for differences in prescription values between regimens. Due to the small sample size, distributions were compared using a nonparametric Wilcoxon matched pairs test with statistical significance at p-value<0.05.
Results: Tumors characteristics were as follows [range (median)]: (a) maximum clinical basal diameter [6.7-15.8mm (9.7mm)]; (b) tumor height [1.1-10.75mm (3.4mm)]; and (c) OD-tumor distance [1.2-14mm (4.6mm)]. Dmax to OD was significantly different for protons versus plaques (p=0.01). Median (range) for Dmax OD was 0 GyE(0-52.1GyE) for protons and 40Gy(10-120Gy) for plaques, with 7 proton plans sparing the disc. Dmax/%Rx OD was also significantly different, 0%(0-93) and 47.1%(11.8-141.2) for protons and plaques, respectively (p=0.01). Dmax and Dmax/%Rx to macula was significantly different between protons and plaques, (p=0.01 and p=0.03, respectively) with the latter metric at 56%(0-94) versus 64.7%(11.8-225.9), respectively. Dmax to lens was significantly different at 2.8 GyE(0-56) for protons versus 16Gy(9-90) for plaques, respectively (p=0.02); Dmax/%Rx to lens did not differ at 5%(0-100) versus 18.8%(10.6-105.9), (p=0.37).
Conclusion: Dedicated eye proton beam plans demonstrated significantly different dose distributions compared with I-125 plaque plans with increased critical structure sparing and lower median doses for the optic disc and macula for both Dmax and Dmax/%Rx, and Dmax to lens.