Dose-response effect of human equivalent radiation in the murine mandible: Part II. A biomechanical assessment.

BACKGROUND: Despite the widespread use of adjuvant irradiation for head and neck cancer, the extent of damage to the underlying bone is not well understood. However, patients can suffer serious clinical consequences, including pathologic fractures, nonunion, and osteoradionecrosis. The authors' specific aim was to objectively quantify the human equivalent radiation dose-response effect of radiation on the biomechanical properties of the murine mandible.
METHODS: Twelve Sprague-Dawley rats were randomized into three radiation dosage groups--low (5.91 Gy), middle (7 Gy), and high (8.89 Gy)--delivered in five daily fractions. The fractionation regimen was used to approximate 75, 100, and 150 percent, respectively, of the bioequivalent dose humans receive in conventional head and neck cancer treatment. Fifty-six days after irradiation, hemimandibles were loaded to failure in a uniaxial tension at 0.5 mm/second. Load displacement curves were analyzed for yield and breaking load, and values were considered statistically significant at p<0.05.
RESULTS: The authors' data demonstrated a statistically significant decrease in the yield and breaking load metrics. The authors' reported averages for low, middle, and high radiation dosages were 162, 136, and 69 N, respectively, for yield; and 215, 211, and 141 N, respectively, for breaking load. Both of these quantitative biomechanical properties were diminished in a dose-response pattern.
CONCLUSIONS: In this article, the authors report a dose-response effect in the degradation of the biomechanical properties of the mandible after fractionated human equivalent radiation. The authors' findings and model can now be used to formulate therapies aimed at remediating those effects and augmenting bone regeneration and healing after adjuvant radiotherapy in head and neck cancer patients.