Purpose: To investigate the application of MLC logfiles as an alternative method for patient-specific QA (PSQA).
Methods: Fifty-four patients treated were included in this study. For each treatment 2 VMAT beams were used for the delivery of the prescribed dose. PSQA was completed using the Delta4 phantom and the evaluation of the gamma index was performed using 2% dose difference (DD) and 2mm distance to agreement (DTA). For each delivery, we captured the logfiles using the iCom interface of the ELEKTA linac and performed the analysis using the Standard Imaging LinacView system. (see Figure 1) The LinacView calculated fluence of each beam was compared against the one by the treatment planning system (RaySearch v9.2).
Results: The average passing rate between the two systems were calculated to be 97.7 2.4 for Delta4 and 94.1 4.7 for the LinacView. (figure 2) It was observed that the gamma index between the two systems had a weak correlation. (Figure 3) The first VMAT beam gamma index had a higher percentage of gamma index passing rate compared to the 2nd one for both methods of evaluation. The number of MU was also on average higher for the first beam compared to the second. The difference between the gamma index of the first VMAT beams between Delat4 and LinacView was 2.4% and 5.0% for the second.
Conclusion: In general, the LinacView logfiles were able to predict that a VMAT beam would pass the PSQA criteria when measured with the Delta4 phantom at a rate of 85%. Additional data will be acquired to further validate the new method of PSQA before clinical implementation.
Not Applicable / None Entered.