Verification of Qfix Encompass™ couch modeling using the Acuros XB algorithm and HypeArc™ using a high-spatial-resolution two-dimensional diode array

• Published in: Medical dosimetry : official journal of the American Association of Medical Dosimetrists
• Main Authors: Yamada, Takumi, Nakano, Hisashi, Tanabe, Satoshi, Sakai, Tatsuya, Tanabe, Shunpei, Oka, Tetsuya, Sakai, Hironori, Oshikane, Tomoya, Nakano, Toshimichi, Ohta, Atsushi, Kanazawa, Tsutomu, Kaidu, Motoki, Ishikawa, Hiroyuki
• Format: Journal Article
• Language: English
• Published: United States 01.01.2023
• Subjects: Acuros XB; Couch model; Single-isocenter irradiation; Brain metastasis; SRS MapCHECK; HyperArc
• ISSN: 1873-4022
• DOI: 10.1016/j.meddos.2023.06.002

We modeled the Qfix Encompass™ immobilization system and further verified the calculated dose distribution of the AcurosXB (AXB) dose calculation algorithm using SRS MapCHECK (SRSMC) in the HyperArc™ (HA) clinical plan. An Encompass system with a StereoPHAN™ QA phantom was scanned by SOMATOM go.Sim and imported to an Eclipse™ treatment planning system to create a treatment plan for Encompass modeling. The Encompass modeling was performed in the StereoPHAN with a pinpoint ion chamber for 6 MV and 6 MV flattening filter free (6 MV FFF), and 2 × 2 cm , 4 × 4 cm , and 6 × 6 cm irradiation field sizes. The dose calculation algorithm used was AXB ver. 15.5 with a 1.0 mm calculation grid size. The Hounsfield unit (HU) values of the Encompass modeling were set to 400, -100, -200, and -300 for Encompass, and -400, -600, -700, and -800 for the Encompass base. We evaluated the dose distribution after Encompass modeling by SRSMC using gamma analysis in 12 patients. We adopted HU values of -200 for Encompass, -800 for Encompass base for 6 MV, and -200 for Encompass and -700 for Encompass. Base for 6 MV FFF was adopted as the HU values for the Encompass modeling based on the measurement results. The proposed Encompass modeling resulted in a mean pass rate evaluation >98% for both 6 MV and 6 MV FFF when the 1%/1 mm criterion was used, demonstrating that the proposed HU value can be adopted to calculate more accurate dose distributions.