Dose variation at bone/titanium interfaces using titanium hollow screw osseointegrating reconstruction plates

Area of Science:

• Biomaterials Science
• Medical Physics
• Oral and Maxillofacial Surgery

Background:

• Mandibular reconstruction often involves titanium implants.
• Postoperative radiotherapy is sometimes used in head and neck cancer treatment.
• Potential interactions between radiotherapy and bone-implant interfaces require investigation.

Purpose of the Study:

• To quantify radiation dose variations at bone/titanium interfaces.
• To evaluate these variations in an experimental model simulating radiotherapy after mandibular reconstruction.
• To assess the impact of the titanium hollow-screw osseointegrating reconstruction plate (THORP) system.

Main Methods:

• An experimental model using bovine femoral bone and a THORP system was developed.
• Thermoluminescent dosimeters (TLDs) measured doses at various distances from the screw axis.
• 60Co and 6-MV photon beams were used with perpendicular and axial incidences relative to the screw axis.

Main Results:

• Perpendicular incidence: Maximum dose enhancement of 5-6% and reduction of 6-10% for 6-MV and 60Co beams, respectively.
• Axial incidence: Maximum dose enhancement of 5-7% when beams hit the plate surface, and 2-3% for opposite surface incidence.
• All measured dose variations were close to the TLD method's uncertainty limits (+/- 5%).

Conclusions:

• Dose variations at bone/titanium interfaces around THORP screws are marginally significant.
• Dose variations were smaller for axial incidences compared to perpendicular incidences.
• Results suggest that overdosage at the bone/titanium interface is unlikely to be the cause of prosthetic osseointegration failures.