The success of radioactive seeds in the treatment of equine skin tumors described

An equine sarcoid. Image: Malcolm_Morley, CC BY-SA 3.0, via Wikimedia Commons

High dose rate brachytherapy appears to be an attractive option for the treatment of skin tumors in horses, according to a clinical commentary.

High dose rate brachytherapy is a form of radiation therapy that uses implanted radioactive seeds to deliver maximum radiation to a tumor for a short time. Typically, this is local anesthesia, with catheters placed under the skin and in or near the cancer.

The seeds, the size of a grain of rice, are inserted into the catheter for several minutes and then removed. Patients can receive multiple treatments and are not radioactive after seed removal.

The procedure is an established technique for treating skin tumors in human medicine, Dr. Anna Hollis noted in a journal comment. Equine veterinary education. Hollis, from the Department of Veterinary Medicine at Cambridge Equine Hospital, part of the University of Cambridge, said squamous cell carcinomas and basal cell carcinomas respond particularly well, with cure rates of 96-98% and excellent aesthetic results. The results, she says, compare extremely favorably to surgery.

“Indeed, in non-malignant human skin cancer, high dose rate brachytherapy is often the treatment of choice for lesions that cannot be surgically removed without severe defects, that require cosmetic and/or reconstructive procedures. .”

Compared to external radiotherapy, brachytherapy has a favorable dose distribution, with better radiological coverage of the tumor and better protection of surrounding tissues at risk of secondary radiological damage.

“The ability to treat large tumors with minimal adverse effects on surrounding normal tissue and a high likelihood of cure with high dose rate brachytherapy makes it an attractive option for equine skin tumors,” says Hollis.

Interstitial brachytherapy, in which the radiation source is placed directly into the tumor, is theoretically the ideal technique for radiation therapy of equine tumors, she says, because a high dose of radiation can be delivered precisely and safely to the tumor. tumor in a relatively short time.

The technique, she adds, is relatively simple and the radioactive material can be delivered to the tissues without requiring any operator exposure, making it much safer and more convenient than traditional brachytherapy techniques. at low dose rate.

In humans, CT imaging is performed as standard once the applicators are in position to allow for accurate treatment planning. However, in horses this is unlikely to be possible, financially viable or practical in most cases. Hollis says there are other imaging options. Although they have reduced accuracy compared to computer-assisted methods, they may be more appropriate in locations where the underlying tissues are less radiosensitive.

Hollis notes that high dose rate brachytherapy was briefly described for the treatment of equine skin tumors in 1998, and two small case series were published in 2017 on its use in the treatment of equine sarcoids.

Hollis said she has also used the technique in horses with good success rates in more than 140 sarcoid and squamous cell carcinomas (her data is unpublished).

She notes that a variety of other tumors in dogs have been treated with this technique, including carcinomas, various sarcomas, mast cell tumors, lymphomas, and melanomas, citing a 2019 paper. However, to her knowledge, there is only one report of its use for the treatment of dermal hamartomas (local malformations consisting of an abnormal mixture of cells and tissues) in any veterinary species.

In humans, hamartomas in various locations have been successfully treated with different forms of radiation therapy, she notes, including high-dose-rate brachytherapy.

“In the majority of veterinary reports of hamartomas, including those in horses, surgery has been performed as the treatment of choice.

“However, in the case of recurrent lesions or for which surgical excision is not possible due to their location, high dose rate brachytherapy seems to be a safe and effective method of treatment, where this technique is available. .”

Hollis, AR (2022), High dose rate brachytherapy for the treatment of skin tumors in humans and animals. Equine Vet Educ, 34: 402-403. https://doi.org/10.1111/eve.13596

The comment, published under a Creative Commons Licensecan be read here.