Dosimetric evaluation of Acuros XB Advanced Dose Calculation algorithm in heterogeneous media

Abstract

Background: A study was realised to evaluate and determine relative figures of merit of a new algorithm for photon dose calculation when applied to inhomogeneous media.

Methods: The new Acuros XB algorithm implemented in the Varian Eclipse treatment planning system was compared against a Monte Carlo method (VMC++), and the Analytical Anisotropic Algorithm (AAA). The study was carried out in virtual phantoms characterized by simple geometrical structures. An insert of different material and density was included in a phantom built of skeletal-muscle and HU = 0 (setting "A"): Normal Lung (lung, 0.198 g/cm3); Light Lung (lung, 0.035 g/cm3); Bone (bone, 1.798 g/cm3); another phantom (setting "B") was built of adipose material and including thin layers of bone (1.85 g/cm3), adipose (0.92 g/cm3), cartilage (1.4745 g/cm3), air (0.0012 g/cm3). Investigations were performed for 6 and 15 MV photon beams, and for a large (13 × 13 cm2) and a small (2.8 × 13 cm2) field.

Results: Results are provided in terms of depth dose curves, transverse profiles and Gamma analysis (3 mm/3% and 2 mm/2% distance to agreement/dose difference criteria) in planes parallel to the beam central axis; Monte Carlo simulations were assumed as reference. Acuros XB gave an average gamma agreement, with a 3 mm/3% criteria, of 100%, 86% and 100% for Normal Lung, Light Lung and Bone settings, respectively, and dose to medium calculations. The same figures were 86%, 11% and 100% for AAA, where only dose rescaled to water calculations are possible.

Conclusions: In conclusion, Acuros XB algorithm provides a valid and accurate alternative to Monte Carlo calculations for heterogeneity management.

Figure 1

Geometrical layout of the phantoms. Phantom A on the left; phantom B in the middle; sectors used in the 2D gamma analysis for phantom A on the right.

Figure 2

Depth dose curves (DD) as dose to medium, dose to water, dose rescaled to water. Calculations with Acuros XB version 10 algorithm: (A) Phantom A: in columns: Normal Lung, Light Lung, Bone; in rows: SF and LF for 6X, SF and LF for 15X. (B) Phantom B: in columns: SF, LF; in rows: 6X, 15X.

Figure 3

EGSnrc and VMC++ comparison. Depth dose curves (DD) at -4 cm off-axis for the SF, 6X case in Normal Lung, Light Lung and Bone for EGSnrc and VMC++.

Figure 4

Depth dose curves (DD) at -4 cm off-axis. Dose to medium calculations for VMC++, Acuros XB version 10, and AAA in phantom A. In columns: Normal Lung, Light Lung, Bone; in rows: SF and LF for 6X, SF and LF for 15X.

Figure 5

Profiles at mid-depth of the heterogeneity insert. Dose to medium calculations for VMC++, Acuros XB version 10, and AAA in phantom A. In columns: Normal Lung, Light Lung, Bone; in rows: SF and LF for 6X, SF and LF for 15X.

Figure 6

Depth dose curves (DD) at beam central axis. Dose to medium calculations for VMC++, Acuros XB version 10, and AAA in phantom B. In columns: SF, LF; in rows: 6X, 15X.

Figure 7

Depth dose curves (DD) at -4 cm off-axis. Dose to medium calculations for VMC++, Acuros XB versions 10 and 11 in phantom A. In columns: Normal Lung, Light Lung, Bone; in rows: SF and LF for 6X, SF and LF for 15X.

Figure 8

Profiles at mid-depth of the heterogeneity insert. Dose to medium calculations for VMC++, Acuros XB versions 10 and 11 in phantom A. In columns: Normal Lung, Light Lung, Bone; in rows: SF and LF for 6X, SF and LF for 15X.

Figure 9

Depth dose curves (DD) at beam central axis. Dose to medium calculations for VMC++, Acuros XB versions 10 and 11 in phantom B. In columns: SF, LF; in rows: 6X, 15X.

Figure 10

Gamma maps. Examples for LF, 15X, dose to medium, Acuros XB version 10 vs. VMC++. Thresholds 2 mm, 2% as global gamma computations. White lines represent the heterogeneity interfaces.

Figure 11

Histograms of the GAI. Global gamma calculation for each sector of phantoms A and B, for dose to medium calculations for Acuros XB version 10 (red horizontal hatching) and AAA (green diagonal hatching). Each bin represents the two threshold results of 2%, 2 mm (thin cross-hatching) and 3%, 3 mm (thick cross-hatching). In columns: Normal Lung, Light Lung, Bone, phantom B; in rows: SF and LF for 6X, SF and LF for 15X.