Dose difference between anisotropic analytical algorithm (AAA) and Acuros XB (AXB) caused by target's air content for volumetric modulated arc therapy of head and neck cancer.

BACKGROUND

We clarified the dose difference between the anisotropic analytical algorithm (AAA) and Acuros XB (AXB) with increasing target's air content using a virtual phantom and clinical cases.

MATERIALS AND METHODS

Whole neck volumetric modulated arc therapy (VMAT) plan was transferred into a virtual phantom with a cylindrical air structure at the center. The diameter of the air structure was changed from 0 to 6 cm, and the target's air content defined as the air/planning target volume (PTV) in percent (air/PTV) was varied. VMAT plans were recalculated by AAA and AXB with the same monitor unit (MU) and multi-leaf collimator (MLC) motions. The dose at each air/PTV (5%-30%) was compared between each algorithm with D, D, D and D for the PTV. In addition, MUs were also compared with the same MLC motions between the D prescription with AAA (AAA_D), AXB_D, and the prescription to 100% minus air/PTV (AXB_D) in clinical cases of head and neck (HNC).

RESULTS

When air/PTV increased (5-30%), the dose differences between AAA and AXB for D, D, D and D were 3.08-15.72%, 2.35-13.92%, 0.63-4.59%, and 0.14-6.44%, respectively. At clinical cases with air/PTV of 5.61% and 28.19%, compared to AAA_D, the MUs differences were, respectively, 2.03% and 6.74% for AXB_D and 1.80% and 0.50% for AXB_D.

CONCLUSION

The dose difference between AAA and AXB increased as the target's air content increased, and AXB_D resulted in a dose escalation over AAA_D when the target's air content was ≥ 5%. The D of PTV using AXB was comparable to the D of PTV using AAA.