The irreplaceable art of brachytherapy: A technical note on interstitial high-dose-rate interventional radiotherapy (brachytherapy) in eyelid tumors

Purpose:
Eyelid tumors are uncommon malignancies, where 75% of cases are cutaneous basal cell carcinoma (BCC), and sebaceous cell carcinoma, squamous, adenocarcinoma from meibomian glands are diagnosed in 25%. Post-excision adjuvant radiotherapy (ART) is indicated in high-grade tumors with positive margins and lymphovascular space or perineural invasion. The ideal technique for delivering ART for eyelid tumors is interstitial brachytherapy (ISBT). However, its use is limited by steep learning curve. Here, we described the stepwise procedure of ISBT performed in eyelid tumors with reported outcomes.

Material and methods:
Four patients with sebaceous carcinoma of the upper eyelid underwent ART, and 2 of the 4 patients had positive margins. Tumor bed was delineated with a 0.5-1 cm margin circumferentially. Under short general anesthesia, 2-3 hollow ISBT needles were inserted in a single-plane into tumor bed, 1 cm apart. Tarsal margin was avoided by > 2 mm to prevent eyelid contractures. Needles were replaced with 6 Fr flexible nylon catheters and fixed with buttons, ensuring a 5 mm gap from the skin to allow post-procedural edema. 3.5 Gy in 12-14 fractions were planned to achieve EQD₂ dose of 60 Gy for R0 resection and 66 Gy for R1 resection, delivered twice a day with more than 6 hours interval. A wax-coated lead shield was placed to protect the cornea and lens using 0.4% paracaine eye drops. In vivo dosimetry was performed using metal-oxide-semiconductor field-effect transistor (MOSFET).

Results:
The mean clinical target volume (CTV) was 2.1 cc, the target D₉₀ was 3.37 Gy/fraction. The target V100% was 86.27%, V150% was 31%, and V200% was 11.33%. The lens D_max (TPS) was 1.28 Gy/fraction, while the mean dose recorded by MOSFET was 0.7 Gy/fraction. No conjunctival acute toxicities were observed. Grade 1 skin reaction (hyperpigmentation) was noted, with no local recurrences at 1 year median follow-up.

Conclusions:
ART delivered by ISBT in eyelid tumors is a simple and efficient brachytherapy procedure, providing excellent cosmesis and local control.