Intratumoral injection of radioactive holmium ( 166Ho) microspheres for treatment of oral squamous cell carcinoma in cats

Background & AimsA microbrachytherapy was developed as treatment option for inoperable tumours by direct intratumoral injection of radioactive holmium-166 ( Ho-166) microspheres (MS). Ho-166 emits -radiation which potentially enables a high, ablative, radioactive-absorbed dose on the tumour tissue while sparing surrounding tissues. Materials & MethodsSafety and efficacy of Ho-166 microbrachytherapy were evaluated in a prospective cohort study of 13 cats with inoperable oral squamous cell carcinoma without evidence of distant metastasis. ResultsLocal response rate was 55%, including complete response or partial response (downstaging) enabling subsequent marginal resection. Median survival time was 113days overall, and 296days for patients with local response. Side effects were minimal. Tumour volume was a significant predictor of response. DiscussionResponse rate may be further improved by optimizing the intratumoral spatial distribution of Ho-166 MS. Conclusion(166)Ho microbrachytherapy has potential as a minimally invasive, single procedure radio-ablation treatment of unresectable tumours with minimal morbidity.