Room: Exhibit Hall
Purpose: To evaluate TrueBeam machine performance check (MPC) for machine output and KV imaging offset checks.
Methods: MPC was run daily over a period of 6 months (n=139) in parallel with DailyQA3 device and in-house CBCT imaging QA for daily machine output on 6X and KV imaging offset checks. MPC and DailyQA3 were baselined on the same day back to back. Machine output constancy measured by MPC was compared against that measured by DailyQA3. Linear regression analysis was performed between MPC and DailyQA3. In addition, MPC was run twice per day (morning and afternoon, before and after patient treatment) in random selected 15 days to evaluate performance reproducibility. MPC KV imaging offset check was evaluated against our in house CBCT QA results.
Results: Over the period of 6 months, MPC 6X beam output was found to agree with DailyQA3 measurement within 0.65%, with mean (SD) of 0.02% (0.27%). Machine output drifted about 2% in the first 4 months of use (as measured monthly with an ion chamber and daily with DailyQA3). MPC was able to detect the output drift accurately. Linear regression between output constancy measured by MPC and by DialyQA3 shows a coefficient of 1.000 and R2 value of 0.851. Difference of morning and evening MPC output constancy check measurements was in the range of 0.01% to 0.39%, which is within the expected magnitude of daily machine output variations. Mean (SD) of KV imaging offset was measured as 0.030 (0.004) cm and 0.079 (0.034) cm by MPC and in-house CBCT QA, respectively. MPC results agree with the CBCT QA results with mean (SD) of 0.034(0.049) cm. MPC results were found to have much less deviations compared with our in-house CBCT QA.
Conclusion: MPC proved to be reliable for machine output and KV imaging offset check over the evaluation period.
TH- External beam- photons: Quality Assurance - Linear accelerator