The effect of material assignment in nasal cavity on dose calculation for nasopharyngeal carcinoma (NPC) using Acuros XB

Purpose To evaluate the effect of material assignment in nasal cavity on dose calculation for the volumetric modulated arc therapy (VMAT) of nasopharyngeal carcinoma (NPC) using Acuros XB (AXB) algorithm. Methods The VMAT plans of 30 patients with NPC were calculated using AXB with material auto-assignment of nasal cavity to lung and reassignment to air respectively. The doses to the planning target volumes (PTVs) overlapping with nasal cavity with material auto-assignment of lung (AXB_Lung) were compared to the values obtained when nasal cavity was reassigned to air (AXB_Air) under the dose-to-medium (D-m) reporting mode of AXB. Results For dose calculated under AXB_Lung, the D-98%, D-2%, and D-mean of the PTV69.96_Air Cavity (PTV of prescription dose 69.96 Gy overlapping with nasal cavity) were on average 16.1%, 1.6%, and 8.6% larger than that calculated under AXB_Air, respectively. Up to 19.5% difference in D-98%, 3% difference in D-2%, and 11.2% difference in D-mean were observed in the worst cases for PTV69.96. Similar trend was observed for the PTV5940_Air Cavity, in which the D-98%, D-2%, and D-mean calculated under AXB_Lung were on average 14.7%, 2.5%, and 10.2% larger than that calculated under AXB_Air, respectively. In the worst cases, the difference observed in D-98%, D-2%, and D-mean could be up to 17.7%, 4.5%, and 12.7%, respectively. Conclusions Significant dose difference calculated by AXB between the material assignment of lung and air in nasal cavity for NPC cases might imply the possibility of underdosage to the PTVs that overlap with inhomogeneity. Therefore, attention should be put to ensure that accurate material assignment for dose calculation under AXB such that optimal dosage was given for tumor control.

Automated summary

This study evaluated the impact of material assignment in the nasal cavity on dose calculation for nasopharyngeal carcinoma treatment using the Acuros XB algorithm. The results showed that assigning the nasal cavity to the lung instead of air resulted in higher calculated doses. This could potentially lead to underdosing of the target volumes, highlighting the importance of accurate material assignment in dose calculation.