Correlation of the gamma passing rates with the differences in the dose-volumetric parameters between the original VMAT plans and actual deliveries of the VMAT plans

• Published in: PloS one 2020-12, Vol.15 (12), p.e0244690-e0244690
• Main Authors: Park, Jong Min, Choi, Chang Heon, Wu, Hong-Gyun, Kim, Jung-In
• Format: Article
• Language: English
• Subjects: Biology and Life Sciences; Biomedical research; Cancer; Care and treatment; Collimation; Correlation; Correlation analysis; Correlation coefficient; Correlation coefficients; Dosage; Drug dosages; Exocrine glands; Gamma Rays; Head & neck cancer; Head and neck cancer; Head and Neck Neoplasms - diagnostic imaging; Head and Neck Neoplasms - radiotherapy; Humans; Image Processing, Computer-Assisted; Mathematical analysis; Measurement; Medical research; Medicine; Medicine and Health Sciences; Oncology; Parameters; Parotid gland; Physiological aspects; Properties; Radiation therapy; Radiotherapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy, Intensity-Modulated; Research and Analysis Methods; Retrospective Studies; Salivary glands; Sensors; Throat cancer; Tomography, X-Ray Computed
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0244690

The aim of this study was to investigate the correlations of the gamma passing rates (GPR) with the dose-volumetric parameter changes between the original volumetric modulated arc therapy (VMAT) plans and the actual deliveries of the VMAT plans (DV errors). We compared the correlations of the TrueBeam STx system to those of a C-series linac. A total of 20 patients with head and neck (H&N) cancer were retrospectively selected for this study. For each patient, two VMAT plans with the TrueBeam STx and Trilogy (C-series linac) systems were generated under similar modulation degrees. Both the global and local GPRs with various gamma criteria (3%/3 mm, 2%/2 mm, 2%/1 mm, 1%/2 mm, and 1%/1 mm) were acquired with the 2D dose distributions measured using the MapCHECK2 detector array. During VMAT deliveries, the linac log files of the multi-leaf collimator positions, gantry angles, and delivered monitor units were acquired. The DV errors were calculated with the 3D dose distributions reconstructed using the log files. Subsequently, Spearman's rank correlation coefficients (rs) and the corresponding p values were calculated between the GPRs and the DV errors. For the Trilogy system, the rs values with p < 0.05 showed weak correlations between the GPRs and the DV errors (rs 0.6) with the GPRs with gamma criteria except 3%/3 mm. As the GPRs increased, the DV errors decreased. The GPRs showed strong correlations with some of the DV errors for the VMAT plans for H&N cancer with the TrueBeam STx system.