Iridium-192 interstitial brachytherapy for equine periocular tumours: treatment results and prognostic factors in 115 horses.

This research article reports the results of a study examining the effectiveness of iridium-192 interstitial brachytherapy for treating periocular tumours in horses, with a specific focus on the prognostic factors that impact the treatment’s success rate.

Study Design and Participants

• The researchers treated 115 horses with periocular (around the eye) tumours using iridium-192 interstitial brachytherapy, which involves the internal application of radiation to destroy cancer cells.
• Of the 115 horses, 52 had squamous cell carcinomas, and 63 had sarcoids – both of which are forms of skin cancer.
• All horses were scheduled to receive a minimal tumour dose of 60 Gy of radiation at a low dose rate.

Methodology and Results

• Follow-up times to last contact or death had a mean of 24 months and a median of 16 months.
• Chronic radiation reactions observed included palpebral fibrosis, cataract, keratitis and corneal ulceration. Cosmetic changes observed included permanent epilation and hair dyspigmentation.
• The progression-free survival (PFS) rates after one year for horses with sarcoids and carcinomas were 86.6% and 81.8%, whilst the five-year PFS rates were 74.0% and 63.5% respectively.

Analysis of Prognostic Factors

• The researchers examined a variety of prognostic factors, including horse age and sex, histopathological type, anatomical subsite, and tumour classification according to the World Health Organization (WHO) T1-3 scale.
• The only significant prognostic factor that independently affected PFS time was the WHO T-classification.
• Horses with T2 and T3 lesions had 1.8-fold and 3.4-fold increased risks of tumour recurrence when compared to those with T1 lesions.
• The one-year PFS rates for T1, T2 and T3 lesions were 95.2%, 89.5% and 66.2%, respectively, while the five-year PFS rates were 72.2%, 74.0% and 53.1%.

Conclusion

• The results of the study suggest that irradiation is an effective treatment for horses with T1-2 lesions. However, for horses with T3 lesions, irradiation should be used as part of a combined treatment modality due to the increased risk of tumour recurrence.