Medium-Term Stability of the Photon Beam Energy of An Elekta Compact™ Linear Accelerator Based on Daily Measurements of Beam Quality Factor

Introduction: In this study, we aimed to assess the medium-term energy stability of a 6MV Elekta Compact™ linear accelerator. To the best of our knowledge, this is the first published article to evaluate this linear accelerator in terms of energy stability. As well as investigating the stability of the linear accelerator energy over a period of several weeks, the results will be useful for estimation of the required tolerance values for the beam quality factor (BQF) of the PTW QUICKCHECK webline™ (QCW) daily checking device. Materials and Methods: Over a 13 week period of routine clinical service, 52 daily readings of BQF were taken and then analyzed for a 10×10 cm^2 field. Results: No decreasing or increasing trend in BQF was observed over the study period. The mean BQF value was estimated at 5.4483 with a standard deviation (SD) of 0.0459 (0.8%). The mean value was only 0.1% different from the baseline value. Conclusion: The results of this medium-term stability study of the Elekta Compact linear accelerator energy showed that 96.2% of the observed BQF values were within ±1.3% of the baseline value. This can be considered to be within the recommended tolerance for linear accelerator photon beam energy. If an approach of applying ±3 SD is taken, the tolerance level for BQF may be suggested to be set at ±2.5%. However, further research is required to establish a relationship between BQF value and the actual changes in beam energy and penetrative quality.