Perturbation Effect of Fiducial Marker on 3D Dose Distribution in External Surrogates Radiotherapy

Tumor motion is a challenging issue in radiotherapy, which complicates the process of tumor delineation, localization, and dose delivery. External surrogate radiotherapy is one of the available strategies that provides motion dataset for a consistent prediction model to track tumor motion using internal-external markers. Regarding this, the present study was conducted to investigate the effect of implanted fiducial on 3D uniform dose distribution.

For the purpose of the study, a Monte Carlo code was utilized to simulate clip with different dimensions and material structures against four therapeutic beams. Moreover, a combinational clip made of golden and covered by polymethyl methacrylate (PMMA) was proposed to be used with lower dose perturbation. Finally, it was proposed to implant a clip outside tumor volume at specific distances from tumor site to keep dose uniformity on tumor volume. To investigate this issue, the correlation coefficient parameter was calculated as the metric among the motion dataset of tumor and clip.

Based on the results, dose perturbation caused by implanted clip was remarkable at hadron therapy depending on its size and material, mainly at the downstream part of the clip.

As the findings indicated, the golden marker covered with PMMA could remarkably reduce dose perturbation. The most important concern in this domain is the presence of a possible correlation between tumor motion and motion of the clip implanted outside the tumor volume. The results of the correlation coefficient revealed a close relationship between tumor motion and clip motion.