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

Brachytherapy. 2017 Sep-Oct;16(5):1057-1064. doi: 10.1016/j.brachy.2017.06.014. Epub 2017 Aug 1.

Abstract

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.

Keywords: Brachytherapy; CT-based eye models; Eye models; Eye plaque dosimetry; I-125; Optic disc irradiation; Patient-specific image-based models.

MeSH terms

  • Brachytherapy / methods*
  • Eye Neoplasms / diagnostic imaging*
  • Eye Neoplasms / pathology
  • Eye Neoplasms / radiotherapy*
  • Humans
  • Iodine Radioisotopes / therapeutic use*
  • Ophthalmoscopy
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods*
  • Tomography, X-Ray Computed*

Substances

  • Iodine Radioisotopes
  • Iodine-125