Eye and skin
Pterygium
A wing-shaped growth over the eye that is removed surgically, with a strontium-90 plaque treatment preventing it from coming back.
Definition
A pterygium is a wedge-shaped fibrovascular overgrowth of conjunctiva that extends from the inner or outer corner of the eye onto the cornea, linked to chronic ultraviolet exposure. It causes irritation, redness, astigmatism, and — when it encroaches on the visual axis — blurred vision. Surgical excision alone recurs in a substantial fraction of patients, often more aggressively than the original lesion.
How radiation treats it
Beta irradiation from a strontium-90 ophthalmic applicator, applied immediately after excision, inhibits the proliferating subconjunctival fibroblasts and vascular tissue that drive regrowth. A single, painless surface application reduces recurrence rates from roughly 30–50% with surgery alone to under about 10%. Radiation is directed only to the bare sclera at the excision site, sparing the cornea and lens.
Side effects
- Transient conjunctival redness, irritation, or mild scleral thinning at the treated area.
- Localized avascular zones in the treated sclera are common and usually clinically silent.
- Serious complications such as scleral ulceration or infection are rare with modern fractionation and low total doses.
Simulation process
There is no conventional simulation or planning scan — strontium-90 is a surface-contact beta applicator with a fixed 4–6 mm treatment radius and a very steep dose falloff. After excision, the ophthalmologist and radiation oncologist confirm the bare scleral bed and mark its extent. The applicator size is chosen to cover the excision site with a small margin, and the eye is anesthetized with topical drops for the application.
Treatment process
A common US regimen delivers 30 Gy in three weekly applications of 10 Gy (or single-fraction 10–25 Gy schemes) with the Sr-90 applicator held against the bare sclera for one to two minutes, starting within days of excision. Beta particles penetrate only a few millimeters, so the lens and deep ocular structures receive negligible dose. The patient is observed for healing, with the treated site monitored for recurrence at yearly eye exams.
Key takeaways for students
- Beta (strontium-90) surface application post-excision cuts recurrence dramatically.
- Delivered within days of surgery, before fibroblast regrowth begins.
- Millimeters of penetration — lens and cornea are effectively spared.