Dosimetric Impact of Using the Acuros XB Algorithm for Intensity Modulated Radiation Therapy and RapidArc Planning in Nasopharyngeal Carcinomas

Purpose To assess the dosimetric implications for the intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy with RapidArc (RA) of nasopharyngeal carcinomas (NPC) due to the use of the Acuros XB (AXB) algorithm versus the anisotropic analytical algorithm (AAA). Methods and Materials Nine-field sliding window IMRT and triple-arc RA plans produced for 12 patients with NPC using AAA were recalculated using AXB. The dose distributions to multiple planning target volumes (PTVs) with different prescribed doses and critical organs were compared. The PTVs were separated into components in bone, air, and tissue. The change of doses by AXB due to air and bone, and the variation of the amount of dose changes with number of fields was also studied using simple geometric phantoms. Results Using AXB instead of AAA, the averaged mean dose to PTV70 (70 Gy was prescribed to PTV70 ) was found to be 0.9% and 1.2% lower for IMRT and RA, respectively. It was approximately 1% lower in tissue, 2% lower in bone, and 1% higher in air. The averaged minimum dose to PTV70 in bone was approximately 4% lower for both IMRT and RA, whereas it was approximately 1.5% lower for PTV70 in tissue. The decrease in target doses estimated by AXB was mostly contributed from the presence of bone, less from tissue, and none from air. A similar trend was observed for PTV60 (60 Gy was prescribed to PTV60 ). The doses to most serial organs were found to be 1% to 3% lower and to other organs 4% to 10% lower for both techniques. Conclusions The use of the AXB algorithm is highly recommended for IMRT and RapidArc planning for NPC cases.