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

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• High-Z prosthetic devices in patients receiving radiation therapy pose challenges for accurate dose calculation.
• Modern dose calculation algorithms aim to improve accuracy in complex treatment scenarios.

Purpose of the Study:

• To evaluate the performance of modern dose calculation algorithms when used with high-Z prosthetic devices in radiation treatment planning.
• To compare dosimetric parameters and identify discrepancies introduced by prosthetic devices.

Main Methods:

• A bilateral hip prosthetic patient's CT data was used for treatment plan comparisons across various commercial systems.
• Dosimetric parameters (D98%, D90%, D50%, D2%) for planning target volumes (PTV) and organs at risk (OAR) were analyzed.
• Dose measurements were performed in a water phantom with a prosthetic device using a parallel plate ionization chamber.

Main Results:

• Significant dosimetric variability (>10%) in PTV coverage was observed among different treatment planning algorithms.
• Discrepancies in PTV and OAR dosimetric parameters were noted compared to older algorithms, but with improved homogeneity.
• Measurements showed dose differences <15.7% at high-Z-tissue interfaces due to backscatter and forward scatter attenuation.

Conclusions:

• Modern dose calculation algorithms offer improved dose distributions compared to older ones for high-Z prosthetics.
• Significant differences remain at high-Z-tissue interfaces when comparing calculated doses to measurements.
• Precautions, such as avoiding beam direction through prostheses and using specific algorithm types (Type C), are recommended for accurate radiation delivery.