Monte Carlo-based Design and Comparative Evaluation of Intraoperative Radiotherapy Disks

Intraoperative radiotherapy (IORT) is a technique in which a single high radiation dose (10-20 Gy) is delivered directly to the tumor site during surgery. As this procedure is performed in the operating room, effective protection of the surrounding healthy tissues is of paramount importance. This protection is commonly achieved using shielding disks placed immediately adjacent to the tumor bed, where the material composition of these disks plays a crucial role in determining their shielding effectiveness.

The present study aimed to identify the optimal material combination and thickness for double-layer protective disks in order to maximize healthy tissue protection.

Initially, the LIAC accelerator head, along with its applicator and a water phantom, was modeled using the MCNPX Monte Carlo code. The accuracy of the simulation was validated by comparing the percentage depth dose (PDD) obtained from Monte Carlo simulations with experimental dosimetry data. Optimization was performed by evaluating the transmission factor (TF), backscatter factor (BSF), and absorbed dose. Several new disk configurations-comprising PMMA + lead, PTFE + bismuth, steel + titanium, steel + copper, aluminum + copper, and aluminum + titanium-each with thicknesses of 6 mm and 8 mm, were simulated and compared with a reference disk.

Among all evaluated configurations, the PMMA + lead disk demonstrated the highest attenuation (65.8% at 8 mm thickness), along with the lowest BSF (7.1%) and TF (62.8%), making it the most effective option for protecting healthy tissues.