Pilot study on the in-vitro effect of radiation therapy on bending stiffness of intramedullary photodynamic implants

Photodynamic implants are an increasingly popular minimally invasive option for the surgical treatment of metastatic bone disease. Following surgery, adjuvant radiation therapy (RT) is frequently administered to achieve better disease control and improve patient quality of life, but the role of RT in implant failures associated with photodynamic implants remains unclear. The aim of this study is to determine if the therapeutic RT range of 10-50 Gy affects the biomechanical properties of photodynamic implants. For the experimental group, 15 photodynamic implants were divided evenly into 5 groups that were exposed to different doses of RT (10, 20, 30, 40 and 50 Gy). The control group consisted of 14 non-irradiated photodynamic implants. Four-point bending tests were conducted on all implants to determine bending stiffness. One-way ANOVA was conducted. Bending stiffness (N/mm) mean ± standard deviation for the non-irradiated control group was 38.0 ± 1.2. Bending stiffness (N/mm) mean ± standard deviation for the irradiated experimental groups was 39.2 ± 1.0. No significant difference was found between any groups. RT doses at a range of 10-50 Gy do not affect the bending stiffness of photodynamic implants. The yield and ultimate failure loads were 263.4 ± 5.2 (N) and 305.9 ± 5.5 (N) in the non-irradiated group vs. 266.8 ± 6.4 (N) and 306.8 ± 6.4 (N) in the irradiated group, respectively. The lack of statistical significance in the difference in stiffness, yield, and ultimate load properties among the groups means that it is less likely that RT at the evaluated doses contributes to intrinsic implant failure. Further studies need to be conducted to conclude the potential effect of RT on other mechanical properties of photodynamic implants.