Program Information
Incorporating Patient-Specific CT-Based Ophthalmic Anatomy in Modeling I-125 Eye Plaque Radiotherapy Dose Distributions
C Tien1*, M Astrahan2 , Z Chen1 , R Nath1 , W Liu1 , (1) Yale University School of Medicine, New Haven, CT, (2) Eye Physics, LLC, Los Alamitos, CA.
Presentations
PO-BPC-Exhibit Hall-6 (Saturday, March 18, 2017) Room: Exhibit Hall
Purpose: Improvements in clinical software for I-125 eye plaque brachytherapy treatment planning have included the capability to incorporate patient-specific models based on CT imaging. This study quantifies the dosimetric impact of incorporating patient-specific modeling rather than the conventional stylized standard-model eye.
Methods: Plaque Simulator software was used to retrospectively plan sixteen patients based on a stylized standard eye model. The plan was then translated to a CT-based patient-specific model. Two situations were assumed for the translation: (1) suture eyelet positions were copied from the stylized standard model; (2) the plaque position was repositioned/re-centered to cover the tumor on the patient-specific model. Dosimetric parameters were compared for tumor and healthy ocular structures.
Results: Patient-specific ocular geometry parameters ranged from 0.40 to 1.38 of the stylized standard-model values. If plaques were not re-centered, volume receiving prescription dose (V100%) is, on average, 6.7% different (max: 26%) and D95% is 19.2 Gy different (max: 58.1 Gy). If the plaques were re-centered, the majority (13 of 16) patients had changes in V100% of less than 2%. Half of patients had a dose difference greater than 5% and 5 Gy observed in optic disk max dose. Two patients had maximum optic disk dose differ by more than 35 Gy. The largest differences were observed with a target-to-optic disk distance less than 6 mm. No clinically significant differences (5%/5Gy) were observed for the tumor apex, fovea, lens, and opposing retina.
Conclusion: Dose calculation based on patient-specific CT differed from the stylized standard model, especially if suture coordinates were taken directly from the standard model. It is recommended that a patient-specific model be used for clinical planning, especially when the target-to-optic disk distance is less than 6 mm. With proper CT-based planning, critical organ doses can be reduced and more conformal tumor coverage can be achieved.
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