Author: Sarah A. Ashmeg, Travis James McCaw, Joseph Shields, Matthew Spector, Christopher Tyerech, Christopher T Wilke 👨🔬
Affiliation: UPMC Hillman Cancer Center, UPMC Hillman Cancer Center and University of Pittsburgh School of Medicine, Department of Radiation Oncology, UPMC Hillman Cancer Center, Department of Radiation Oncology, University of Pennsylvania, UPMC 🌍
Purpose: Patients with oral cavity cancer often undergo surgical extirpation prior to radiation, and surgical implants are utilized to reconstruct the resulting defect. This study dosimetrically evaluates the impact of a titanium mandibular implant used in such reconstructions.
Methods: A titanium mandibular implant(KLS 3mm reconstructive plate), 3D printed water-equivalent plastic implant, and combination of solid water and bolus were used to characterize dose enhancement effects. Each implant was placed above 5cm of solid water with 1.5cm of bolus used to simulate a patient’s cheek and provide buildup. MOSFET and EBT3 film dosimeters were positioned on either side of the implant, as well as 0.5cm upstream to evaluate backscatter. A 6X AP field was used. Dose distributions for this setup were also calculated using the Acuros and AAA algorithms in Eclipse treatment planning software with a dose resolution of 0.1cm.
Results: Dose enhancement was observed directly upstream, and dose reduction was observed directly downstream of the metallic implant compared to the plastic implant. MOSFET detectors showed enhancements of 7-8% and shadowing of 10-15% at various locations around the implant. Two separate film measurements showed a maximum of 24 - 26% dose enhancement and 7% dose reduction. Dose uncertainty in the film setup and calibration was measured to be 2-4%. Acuros calculations demonstrated 1-5% enhancement and 5-7% shadowing. AAA calculations showed negligible dose enhancement and 5-7% dose shadowing. No significant dose enhancement was seen 0.5cm upstream of the implant in any measurements.
Conclusion: Significant differences were observed between film measurements and doses predicted by the treatment planning software in the vicinity of reconstructive titanium plates. Such disparities have the potential to cause unintended adverse reactions, such as wound complications to the skin and subcutaneous tissues, as well as underdosing of the treatment bed.