2025 Poster Presentations
P018: COMPARISON OF THE RADIOTHERAPY TECHNIQUES FOR THE TREATMENT OF OCULAR MELANOMA
He Wang; Fahed Alsanea; Amy Catherine Moreno; Dong Joo Rhee; Surendra Prajapati; William Morrison; Parmeswaran Diagaradjane; Dragan Mirkovic; Tina Marie Briere; Rachel Hunter; Jack Phan; Anna Lee; University of Texas M.D. Anderson Cancer Center
Purpose: Eye plaque brachytherapy and external beam radiotherapy(EBRT) are the most used treatment for ocular melanoma to achieve tumor clearance and prevention of metastases while preserving vision. Brachytherapy uses radioactive seed to deliver radiation directly to treatment area with lower risks to healthy tissues nearby, while external beam radiotherapy techniques, including Gamma Knife(GK), CyberKnife, linear accelerator(LINAC), proton beam therapy(PBT), use high energy beams from multiple angles to precisely aim at the target without surgical procedure that is common in brachytherapy. The purpose of this study is to compare the features of different techniques and the dosimetry that can be achieved by GK, LINAC, PBT and eye plaque brachytherapy for ocular melanoma treatment.
Methods: Six patients treated with eye plaque brachytherapy(I-125, 75 – 87 Gy in 120 -140 hours) for ocular melanoma were replanned in RayStation treatment planning system(TPS) to generate volumetric modulated arc therapy(VMAT) photon plans and intensity modulated proton therapy(IMPT) plans, and also replanned in GammaPlan TPS to generate GK plans. VMAT, IMPT and GK plans all used hypofractionated stereotactic radiotherapy setting and were prescribed to 50 Gy in 5 fractions. VMAT plans used 2 non-coplanar arcs, while IMPT used 2-3 non-coplanar beams. Replanned targets had comparable GTV to eye plaques plans, but with 2mm PTV margin, while brachy therapy used 2-3 mm margin along orbit wall and submillimeter margin inwards the eye. The goal of replanning was to achieve as low as possible doses on ipsilateral optic nerves and lens with PTV coverage around or greater than 98%. Treatment techniques and the dosimetric metrics, including target coverage, maximum dose to ipsilateral optic nerve and lens, were compared among the four techniques. While our current proton beamlines had no aperture available, simulated aperture was added and tested to reduce lens dose.
Results: The replanned target volumes were 1.4 cc (range 0.5cc to 3.2cc). The targets located towards medial for 3 patients, and towards lateral for 3 patients relative to optic nerve and lens. PTV coverage of 98% was met for all replans. The mean maximum dose to ipsilateral optic nerve was 66.7%, 42.6%, 25.3% and 33.9% of prescription dose, and the mean maximum dose to ipsilateral lens was 73.0%, 39.5%, 47.8% and 39.0% of prescription dose, for brachy, VMAT, IMPT and GK plans, respectively. The dose to contralateral eye and optic nerve was 6.3%, 0.2% and 3.4% of prescription dose for VMAT, IMPT and GK plans. With simulated brass aperture, the lens doses in IMPT plans were dropped to less than half of those without aperture for targets >3mm away from lens, and the sinus dose was also dropped significantly for medial targets.
Conclusion: External beam radiotherapy and brachytherapy are both effective to treat ocular melanoma. EBRT had the advantages of patient comfort with no surgery procedure involved. Spot scanning IMPT plans with apertures showed superior dose sparing for surrounding organs and lowest dose spread in healthy tissues while still maintaining adequate target coverage. Immobilization of the eyes is essential to ocular treatments when using EBRT techniques.