Comparing Dose Calculation Algorithms for Heterogeneous Media: Analytical Anisotropic Algorithm Versus Acuros XB...

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate dose calculation is critical in radiation therapy, especially in heterogeneous tissues.
• The analytical anisotropic algorithm (AAA) and Acuros XB (AXB) are widely used dose calculation algorithms.
• Variations in CT values significantly impact dose calculations in heterogeneous environments.

Purpose of the Study:

• To compare dose calculations between AAA and two AXB dose reporting modes (AXB(Dm) and AXB(Dw)).
• To evaluate these algorithms across a broad spectrum of CT values (-1000 to 3000 HU) in heterogeneous materials.
• To assess the clinical implications of dose discrepancies in radiation therapy planning.

Main Methods:

• Virtual phantoms with heterogeneous material layers (2 or 5 cm thickness) were created in Eclipse.
• Simulations used single or opposed fields, 5x5 cm² or 10x10 cm² field sizes, and 6 or 10 MV photon energies.
• Relative doses were calculated at the center of the heterogeneous layer and normalized to the dose at 0 HU.

Main Results:

• Pronounced dose differences were observed between AAA and AXB algorithms, particularly for a 5 cm heterogeneous layer with a single 6 MV, 5x5 cm² field.
• In low-density regions (-1000 to -800 HU), AXB showed dose differences of -54.5% (AXB(Dm)) and -47.0% (AXB(Dw)) relative to AAA.
• In high-density regions (1000 to 3000 HU), dose differences ranged from -5.7% to -8.8% (AXB(Dm)) and +7.4% to +3.5% (AXB(Dw)).

Conclusions:

• Significant dose differences exist between AAA and AXB algorithms in heterogeneous materials across a wide CT range.
• These discrepancies highlight a clear risk of under- or over-dosing in clinical applications.
• The study underscores the importance of algorithm selection and verification for patient safety in radiation therapy.