Optic Disc Dose Comparison Between 125I and 103Pd Collaborative Ocular Melanoma Study (COMS) Plaques Based on Current...

Area of Science:

• Ophthalmology
• Radiation Oncology
• Medical Physics

Background:

• Ocular brachytherapy is a treatment for intraocular tumors.
• Collaborative Ocular Melanoma Study (COMS) plaques are used for delivering radiation.
• Understanding dose distribution to critical structures like the optic disc is crucial for treatment planning.

Purpose of the Study:

• To compare the optic disc dose (ODD) delivered by Iodine-125 (¹²⁵I) and Palladium-103 (¹⁰³Pd) COMS plaques.
• To analyze how ODD is affected by varying tumor characteristics and treatment parameters.

Main Methods:

• Utilized an in-house brachytherapy dose calculation program for ODD calculations.
• Calculated ODD based on tumor margin-to-optic disc distance (DT) and basal dimensions (BDs).
• Evaluated standard and notched COMS plaques with ¹²⁵I and ¹⁰³Pd seeds at various prescription depths (2-10 mm).

Main Results:

• ODD trends were similar for both isotopes, but specific transition distances (d_t) existed where ODD values were equal.
• For small tumors, ¹⁰³Pd yielded higher ODD at closer DT, while ¹²⁵I yielded higher ODD at greater DT.
• Notched plaques showed similar ODD reduction trends for both isotopes, with ¹⁰³Pd having a larger maximum reduction.

Conclusions:

• Significant differences in ODD exist between ¹²⁵I and ¹⁰³Pd COMS plaques.
• These dose differences are influenced by the distance to the optic disc (DT), basal tumor dimensions (BD), plaque size, and prescription depth.