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

Poonam Yadav; Mark Pankuch; John McCorkindale; Raj K Mitra; Luther Rouse; Gocha Khelashvili; Bharat B Mittal; Indra J Das

doi:10.1016/j.ejmp.2023.102649

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

Phys Med. 2023 Aug:112:102649. doi: 10.1016/j.ejmp.2023.102649. Epub 2023 Aug 4.

Authors

Poonam Yadav¹, Mark Pankuch², John McCorkindale³, Raj K Mitra⁴, Luther Rouse⁵, Gocha Khelashvili¹, Bharat B Mittal¹, Indra J Das⁶

Affiliations

¹ Department of Radiation Oncology, Northwest Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
² Northwestern Medicine Chicago Proton Center, 4455 Weaver Parkway, Warrenville, IL 60555, USA.
³ Department of Radiation and Cellular Oncology, Northwestern Medicine 1000 N Westmoreland Rd, Lake Forest, IL 60045, USA.
⁴ Department of Radiation Oncology, Ochsner Health System, New Orleans, LA 7012, USA.
⁵ Philips Healthcare, 100 Park Ave, Beachwood, OH 44122, USA.
⁶ Department of Radiation Oncology, Northwest Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA. Electronic address: indra.das@nm.org.

PMID: 37544030
DOI: 10.1016/j.ejmp.2023.102649

Abstract

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.

Keywords: Algorithm; Dosimetry; High-Z implants; Prosthesis; TPS.