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

Abstract

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

Intratumoral injection of radioactive holmium-166 microspheres in recurrent head and neck squamous cell carcinoma

“…Therefore, difficulty in injecting the 166 HoMS suspension was probably caused by a high intratumoral pressure in the firm consistency of the tumor in patient 2. As an increased pressure force can result in needle dislodgement, the injection position was sometimes changed in case of high resistance in the veterinary experience 13 . In patient 3, with soft cutaneous metastases without large ulceration, the injection procedure was feasible.…”

“…Radioactive holmium-166 microspheres ( 166 HoMS) and currently used in intra-arterial radioembolization of liver malignancies 12 . These microspheres emit β radiation with a maximum penetration depth of 8.7 mm and are also used off-label in veterinary patients with unresectable oral squamous cell carcinomas and other tumors 13 , 14 . Intratumoral injections of 166 HoMs in veterinary patients showed a relevant response without severe morbidity 13 .…”

“…These microspheres emit β radiation with a maximum penetration depth of 8.7 mm and are also used off-label in veterinary patients with unresectable oral squamous cell carcinomas and other tumors 13 , 14 . Intratumoral injections of 166 HoMs in veterinary patients showed a relevant response without severe morbidity 13 . This article presents the first experience on the feasibility and safety of intratumoral injections of 166 HoMS in human patients with recurrent cancer in the head and neck.…”

Feasibility of intratumoral 165Holmium siloxane delivery to induced U87 glioblastoma in a large animal model, the Yucatan minipig

“…Holmium (Ho) was selected because it has some advantages over other elements; 1) Ho is a highly paramagnetic isotope, suitable for MRI [44,45], 2) activated holmium ( 166 Ho) is easily obtained following neutron-activation thanks to an adequate neutron capture nuclear reaction known as "cross section" parameter, 3) 166 Ho has a short half-life 26.8 hours and decays rapidly to stable products, 4) 166 Ho deposes 90% of the energy within the range of 2.1 mm and remaining 10% within the range of 2.1-8.6 mm, suggesting that it can intensively irradiate inside the tumor only, whilst preserving the surrounding normal tissue, 5) 166 Ho emits highenergy (1840 MeV) β(-) radiation and low-energy (81 keV) γ radiation [46][47][48][49]. β(-) is an effective means for tumor cell destruction and γ can be used for post-treatment dosimetry and/or patient follow-up thanks to SPECT imaging.…”

Quantitative dual-energy CT material decomposition of holmium microspheres: local concentration determination evaluated in phantoms and a rabbit tumor model

“…A particular therapy that potentially would benefit from DECT quantification is selective internal radiation therapy (SIRT) with beta-emitting radioactive holmium-166 microspheres ( 1 6 6 HoMS), which are currently used for radioembolization of liver tumors and intratumoral injection in solid malignancies [20][21][22][23]. In vivo dosimetry after therapy application, needed to verify the treatment success, can be performed based on SPECT imaging utilizing the holmium-166 gamma radiation or based on magnetic resonance imaging (MRI) utilizing the paramagnetic properties of holmium.…”