Tolerance of Normal Rabbit Facial Bones and Teeth to Synchrotron X-Ray Microbeam Irradiation

Area of Science:

• Veterinary Radiation Oncology
• Preclinical Radiosurgery Research
• Comparative Oncology

Background:

• Microbeam radiation therapy (MRT) is an emerging radiosurgical technique for potential veterinary applications.
• Assessing radiation toxicity to bone and teeth is crucial for safe MRT implementation in pets.
• Muzzle tumors in animals represent a significant clinical challenge requiring novel treatment strategies.

Purpose of the Study:

• To evaluate the long-term radiation toxicity of microbeam arrays on bone and teeth in a preclinical model.
• To determine the safety threshold for microbeam radiation therapy in the facial region of young rabbits.

Main Methods:

• Six rabbits received lateral microplanar beamlet irradiation to the muzzle at peak doses of 200, 330, or 500 Gy.
• Ex vivo micro-computed tomography (micro-CT) and histopathology were used for assessment 431 days post-irradiation.
• Radiation field boundaries were identified histologically by microbeam tracks.

Main Results:

• No radionecrosis of facial bones was observed in any rabbit.
• Caries-like damage occurred in incisors exposed to 330 Gy or 500 Gy, but not at 200 Gy.
• A single array with peak dose ≤200 Gy (valley dose ≤14 Gy) caused no significant damage to bone, teeth, or soft tissues after one year.

Conclusions:

• Microbeam radiation therapy at a peak entrance dose of ≤200 Gy (valley dose ≤14 Gy) appears safe for rabbit muzzle bone, teeth, and soft tissues.
• MRT is unlikely to cause significant damage to normal tissues in pet animals when using these parameters.
• These findings support the preclinical investigation of MRT for treating pet muzzle tumors.