Systematic and comprehensive analysis of the dose-response characteristics of a morning quality check of a linear accelerator and an important application of accelerator performance prediction

Background: This paper aimed to analyze the output constancy of a medical linear accelerator using PTW QUICKCHECKwebline and studied the sensitivity of the PTW QUICKCHECKwebline. Materials and Methods:  The paper statistically analyzed the output doses of 6 MV and 10 MV of photons and 6 MeV, 9 MeV, and 12 MeV of electrons from a medical linear accelerator measured before the daily treatment to assess the output stability of a medical linear accelerator. Some modifications were introduced by artificially altering the external irradiation conditions, and the percent variations from baseline values were noted. The gantry angle was changed and some deviations were established in the vertical, longitudinal and lateral directions to study the sensitivity of the PTW QUICKCHECKwebline. The beam flatness, symmetry, radiation quality and output energy of 6 MV of photon energy were statistically analyzed. Results: Among the measurements, no parameters exceeded the tolerance of ±3%. QUICKCHECKwebline was capable of detecting the variations in the central axis dose, flatness, symmetry and radiation quality under the testing conditions. Similar to the photon energy, electron energy measurements also confirmed that the detector was sensitive to a small variation in output introduced by the testing conditions. An important application of accelerator performance prediction in this study confirms the irreplaceable and important function of morning quality checks of a linear accelerator. Conclusions: The output dose measured before daily treatment using PTW QUICKCHECKwebline to analyze the linear accelerator output constancy helps to decrease the system error, effectively reduces the errors of the accelerator system, and avoids serious mistakes.