Incorporating patient-specific CT-based ophthalmic anatomy in modeling iodine-125 eye plaque brachytherapy dose distributions.

PURPOSE: To quantify the dosimetric impact of incorporating patient-specific CT-based models rather than the conventional stylized-standard model for eye plaque brachytherapy planning.

METHODS AND MATERIALS: Plaque Simulator was used to plan 16 patients using both CT-based patient-specific eye model and stylized-standard (SS) eye models. Plaque position was initially based on the SS model and compared against their patient-specific model without changing the plaque loading pattern and seed strength. Dosimetric parameters were compared for tumor and healthy ocular structures.

RESULTS: Patient-specific ocular parameters ranged from 0.40 to 1.38 of SS model values. If plaques were placed based on SS model eyelet positions, target volume receiving prescription dose (V100% ) is overpredicted by 5.9% on average (max: 27%), and D95% is overpredicted by 17.2 Gy on average (max: 58.1 Gy). If the plaques were recentered, 13 of 16 patients had changes in V100% of less than 2%, whereas half of the patients still had optic disc dose difference greater than 5 Gy (max: 36.2 Gy). The largest differences were observed with a target-to-optic disk distance less than 6 mm. No substantial dose differences were observed for the tumor apex, fovea, lens, and opposing retina.

CONCLUSIONS: Patient-specific modeling is recommended for clinical planning, especially with target-to-optic disk distances less than 6 mm, due to significant differences compared with SS model.