Radiation dose inaccuracies near patient-specific osteosynthesis plates: an ex vivo dosimetric study

Osteoradionecrosis (ORN) inside osseous free flaps and native bone is a severe complication in multimodal therapies for head and neck cancer. The tissue proximity of titanium osteosynthesis plates may influence local radiation dose and planning accuracy, yet data from tissue-equivalent, image-guided models are limited.

An ex vivo dosimetric study was performed using two porcine tibiae, each plated with either one computer aided design and manufacturing (CAD/CAM) patient-specific 2.0 mm reconstruction plate or two 1.0 mm mini plates, thus reproducing the fixation of osseous free flaps in primary mandibular reconstruction prior to radiotherapy. Thermoluminescent dosimeters (TLDs) were placed at seven standardized positions inside and outside the plated bones. Irradiation with a prescribed dose of 2 Gy was performed in soft tissue equivalent environment. Measured doses for all TLD positions were acquired and compared to planned doses from the planning software.

Local dose enhancements in close proximity to osteosynthesis plates were observed in both setups, with measured doses exceeding calculated planned doses by up to 113% in reconstruction plates and 114% in mini plates. Distinct dose deviation patterns of overdosing above the plates, within the bone and underdosing in plate-distant areas compared to planned and prescribed doses were observed in both setups.

In both setups, measured doses exceeded planned and prescribed doses around osteosynthesis plates. These findings underline the need for optimized planning approaches and the potential translational clinical relevance of osteosynthesis materials in postoperative radiotherapy planning and radiotoxicity to bone and surrounding soft tissues.