Simplified sigmoidal curve fitting for a 6 MV FFF photon beam of the Halcyon to determine the field size for beam commissioning and quality assurance

Radiation Oncology

Do-Kun Yoon¹  Tae Suk Suh¹  Min-Geon Choi¹  Moo-Sub Kim¹  Hajime Monzen²  Mikoto Tamura²  Masakazu Otsuka²  Kenji Matsumoto³  Martin Law⁴  Shih-Kien Djeng⁴ 

[1] Department of Biomedical Engineering and Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea;Department of Medical Physics, Graduate School of Medical Sciences, Kindai University, Osaka-Sayama-Shi;Department of Radiology, Kindai University Hospital, Osaka-Sayama-Shi;Proton Therapy Pte Ltd.;

关键词: Field size;    Sigmoidal curve fitting;    FFF;    Halcyon;    Commissioning;    QA;   

DOI  :  10.1186/s13014-020-01709-x

来源: DOAJ

【 摘 要 】

Abstract Background An O-ring gantry-type linear accelerator (LINAC) with a 6-MV flattening filter-free (FFF) photon beam, Halcyon, includes a reference beam that contains representative information such as the percent depth dose, profile and output factor for commissioning and quality assurance. However, because it does not provide information about the field size, we proposed a method to determine all field sizes according to all depths for radiation therapy using simplified sigmoidal curve fitting (SCF). Methods After mathematical definition of the SCF using four coefficients, the defined curves were fitted to both the reference data (RD) and the measured data (MD). For good agreement between the fitting curve and the profiles in each data set, the field sizes were determined by identifying the maximum point along the third derivative of the fitting curve. The curve fitting included the field sizes for beam profiles of 2 × 2, 4 × 4, 6 × 6, 8 × 8, 10 × 10, 20 × 20 and 28 × 28 cm2 as a function of depth (at 1.3, 5, 10 and 20 cm). The field size results from the RD were compared with the results from the MD using the same condition. Results All fitting curves show goodness of fit, R2, values that are greater than 0.99. The differences in field size between the RD and the MD were within the range of 0 to 0.2 cm. The smallest difference in the field sizes at a depth of 10 cm, which is a surface-to-axis distance, was reported. Conclusion Application of the SCF method has been proven to accurately capture the field size of the preconfigured RD and the measured FFF photon beam data for the Halcyon system. The current work can be useful for beam commissioning as a countercheck methodology to determine the field size from RD in the treatment planning system of a newly installed Halcyon system and for routine quality assurance to ascertain the correctness of field sizes for clinical use of the Halcyon system.

【 授权许可】

Unknown