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 (V) is overpredicted by 5.9% on average (max: 27%), and D is overpredicted by 17.2 Gy on average (max: 58.1 Gy). If the plaques were recentered, 13 of 16 patients had changes in V 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.