Comparing Dose Calculation Algorithms for Heterogeneous Media: Analytical Anisotropic Algorithm Versus Acuros XB (Dm/Dw) With Continuous CT Value Variation

Yuya Yanagi; Kazuki Kubo; Takaaki Ito; Kenji Nakamura; Makoto Hirata; Hiroshi Doi; Hajime Monzen

doi:10.7759/cureus.46805

Comparing Dose Calculation Algorithms for Heterogeneous Media: Analytical Anisotropic Algorithm Versus Acuros XB (Dm/Dw) With Continuous CT Value Variation

Cureus. 2023 Oct 10;15(10):e46805. doi: 10.7759/cureus.46805. eCollection 2023 Oct.

Authors

Yuya Yanagi^{1

2}, Kazuki Kubo¹, Takaaki Ito¹, Kenji Nakamura¹, Makoto Hirata¹, Hiroshi Doi³, Hajime Monzen¹

Affiliations

¹ Department of Medical Physics, Graduate School of Medical Sciences, Kindai University, Osakasayama, JPN.
² Department of Radiology, Shiga University of Medical Science Hospital, Otsu, JPN.
³ Department of Radiation Oncology, Faculty of Medicine, Kindai University, Osakasayama, JPN.

Abstract

Background: To compare the doses calculated by the analytical anisotropic algorithm (AAA) and two dose reporting modes of Acuros XB (AXB(D_m) and AXB(D_w)) with varied CT values on the Eclipse (Varian Medical Systems, Palo Alto, CA).

Materials and methods: Virtual phantoms with a central layer of heterogeneous material (thickness = 2 or 5 cm) were created with Eclipse. Using single or opposed fields, the field sizes were 5 x 5 cm² or 10 x 10 cm². The photon energies were 6 or 10 MV, and the source-to-target distance was 100 cm. The relative doses at the center of the heterogeneous material layer were evaluated with varied CT values, from -1000 to 3000 HU. Values were normalized with the dose at 0 HU (100%) for comparative analysis.

Results: The results obtained from continuous data for a single field, 6 MV, 5 x 5 cm², and the heterogeneous material 5 cm, where the differences between algorithms were most pronounced, were as follows. In the low-density region (-1000 HU and -800 HU), the dose differences for AXB with reference to AAA were, respectively, -54.5% and +4.6% (AXB(D_m)) and -47.0% and +3.5% (AXB(D_w)), and in the high-density regions (1000 HU and 3000 HU) were -5.7% and -8.8% (AXB(D_m)) and +7.4% and +3.5% (AXB(D_w)), respectively. Consequently, dose differences at arbitrary CT values could be obtained.

Conclusion: Dose differences between these algorithms were clarified for heterogeneous materials. The risk of dose reduction or escalation in clinical use was clearly visible between CT values from -1000 to 3000 HU.

Keywords: acuros xb (axb); analytical anisotropic algorithm (aaa); ct value; heterogeneous material; hounsfield unit (hu).

Grants and funding

This work was supported in part by the Japan Society for the Promotion of Science (JSPS) KAKENHI grant number 20K08093.