Geant4 Based Dosimetric Analysis of Radiotherapy for Patients with Etmjr Implants
Abstract
Purpose
Radiotherapy in patients with temporomandibular joint reconstruction (TMJR) prostheses introduces unique dosimetric challenges due to the interaction between the radiation beam and high-density implant materials. Different eTMJR prosthesis materials, such as titanium and and stainless steel, can cause dose perturbations, potentially leading to inaccurate dose delivery to both the target area and surrounding healthy tissues. This study investigates the dosimetric impact of titanium and stainless-steel implant materials on radiation dose during external beam radiotherapy across multiple field sizes (5×5, 10×10, 15×15, and 20×20 cm²).
Methods
Using ICRP145 Human Computational Phantom and Medical Linac example of the Geant4 Monte Carlo simulation, we quantified relative dose differences in tumor tissue and critical organs including lymph nodes, salivary glands, pituitary gland, brain, spinal cord, thyroid, eye lens and mandible.
Results
Results demonstrate that titanium implants produce field-size dependent dose perturbations, with significant negative dose differences (-1.3%) at small field sizes that diminish progressively with increasing field dimensions. Stainless steel implants exhibited more consistent dosimetric behavior, with relative dose differences consistently within ±0.2% across all field sizes. Statistical analysis of energy deposition parameters confirmed minimal overall impact on mean energy values (<0.02% variation) despite localized dose perturbations. Percent depth dose verification revealed modest dose enhancement (1-2%) for both materials throughout the therapeutic range (5-25 cm depth), with convergence occurring at superficial and deep regions. Critical neural and endocrine structures showed negligible dosimetric impact with either implant material, supporting the clinical safety profile of both materials.
Conclusion
These findings provide comprehensive characterization of implant-induced dose perturbations and suggest that while both materials introduce measurable dosimetric effects in specific scenarios, these remain within clinically manageable ranges, supporting their continued use in radiotherapy with appropriate consideration during treatment planning.