Radiological Characterization of Tissue Equivalent Materials: A Computational Approach

Phantoms are crucial for accurate assessment of new techniques and for simulating clinical conditions safely while reducing the risk to patients. The study explores the efficacy of different tissue equivalent compositions to mimic actual human tissue for their applications in the medical field.

The material composition nomenclatures as polymethylmethacrylate (PMMA), solid water, SOT, ST, and resin have been employed by researchers for the study of tissue equivalency through different approaches. The computations to evaluate the useful radiological parameters, i.e., mass energy absorption coefficient, computed tomography number, gamma constant, dose rate, effective electron density for gamma rays and stopping power for charged particle ion beams have been done using established computer codes (XCOM [Photon Cross Sections Database] and SRIM/TRIM [Stopping and Range of Ions in Matter]) as well as through newly developed packages (Phy-X/photon shielding and dosimetry [PSD] and Proton, Alpha, Gamma, Electron and X-radiation interaction parameters [PAGEX]).

It is concluded that solid water is the best tissue equivalent phantom material for gamma rays and electrons, while compositions, namely PMMA and ST, are found to be the best tissue equivalents for proton- and alpha particles respectively. The comparison of results obtained from recently developed computer codes (PAGEX and Phy-X/PSD) with established databases confirm their reliability for analysing the phantom materials through a user-friendly approach.

Maximum relative difference of Phy-X/PSD versus XCOM results is found to be <1% for gamma rays (0.02-18 MeV), and for protons (0.05-10 MeV), this difference is ~ 2% among results of PAGEX and SRIM/TRIM. Results would be useful for gamma rays and ion beam-based therapies as well as for the development of new phantom compositions.