Dosimetric evaluation of high-Z inhomogeneity with modern algorithms: A collaborative study

Purpose: To evaluate modern dose calculation algorithms with high-Z prosthetic devices used in radiation treatment.

Methods: A bilateral hip prosthetic patient was selected to see the effect of modern algorithms from the commercial system for plan comparisons. The CT data with dose constraints were sent to various institutions for dose calculations. The dosimetric parameters, D_98%, D_90%, D_50% and D_2% were compared. A water phantom with an actual prosthetic device was used to measure the dose using a parallel plate ionization chamber.

Results: Dosimetric variability in PTV coverage was significant (>10%) among various treatment planning algorithms. The comparison of PTV dosimetric parameters, D_98%, D_90%, D_50% and D_2% as well as organs at risk (OAR) have large discrepancies compared to our previous publication with older algorithms (https://doi.org/10.1016/j.ejmp.2022.02.007) but provides realistic dose distribution with better homogeneity index (HI). Backscatter and forward scatter attenuation of the prosthesis was measured showing differences <15.7% at the interface among various algorithms.

Conclusions: Modern algorithms dose distributions have improved greatly compared to older generation algorithms. However, there is still significant differences at high-Z-tissue interfaces compared to the measurements. To ensure accuracy, it's important to take precautions avoiding placing any prosthesis in the beam direction and using type C algorithms.