Feasibility of Checkmate 2 in Radiotherapy Accelerator Output Check

  Objective  To discuss the feasibility of Checkmate 2 as a daily check device in radiotherapy accelerator output check.

  Methods  According to the methods proposed in International Atomic Energy Agency(IAEA) Report No. 277, Varian 2300CD accelerator's two photon beams (6 MV and 15 MV) and 5 electronic beams (6, 9, 12, 16, and 20 MeV) were calibrated. Ionization chamber and Checkmate 2 were used to measure the output of the beam at 7 energies delivering 100 MU every day. Maximum permissible error was ±2%. Ambient temperature and air pressure were measured and also detected by Checkmate 2 to calculate the correction factor. A total of 66 continuous measurements were carried out in workdays in 3 months to compare the measurements at different energies and accuracy of temperature and air pressure correction factor every day.

  Results  In the measurement results of both Checkmate 2 and ionization chamber, the absolute dose errors were within 2%, and the differences between the two measurement results showed no statistically significant difference (P > 0.05). Measured and Checkmate 2-calculated mean temperature and pressure correction factor were 1.032±0.007 and 1.033±0.007, respectively, with no significant difference(P=0.452). Correlation analysis showed that the two correction factors were positively correlated (r=0.92, P=0.000).

  Conclusions  Checkmate 2 could reflect the dose output with short measurement time and simple operation. It may be applied as a very useful device for linear accelerator output morning check.