Program Information
Clinical Review and Comparison of Quality Assurance Using Dynalog Analysis and Portal Dosimetry
J Monroe1*, E Caspari2 , (1) St. Anthony's Cancer Center, MO; Case Western Reserve University, OH, St. Louis, MO, (2) St. Anthony's Medical Center, St. Louis, Missouri
Presentations
PO-BPC-Exhibit Hall-15 (Saturday, March 18, 2017) Room: Exhibit Hall
Purpose: Patient treatment plans were measured and analyzed using Portal Dosimetry (PD) and Mobius FX (MFx) Dynalog analysis to compare the two methods of quality assurance for clinical use and flow
Methods: Five months of intensity modulated patient plans were measured, pre-treatment, for quality assurance (QA) using both Portal Dosimetry and MobiusFX. A gantry-mounted MapCheck2 (MC2) was used in situations where a third method was required. Clinic policy requires QA for IMRT and VMAT patient plans prior to treatment. 102 patient plans using either sliding window Intensity Modulated Radiotherapy (IMRT) or Volume Modulated Arc Therapy (VMAT) were assigned PD and MFx.The two beam-matched linear accelerators (‘linacs’), a Varian 21EX and Trilogy, are equipped with 120 leaf multileaf collimators. Electronic Portal Imaging Devices (EPID) are used for Portal Dosimetry. All plans are QA’d on both machines unless they were high doserate stereo tactic plans, treatable only on the Trilogy. Varian linacs generate Dynalog files containing machine state information that are copied to MobiusFX server. Dynalog file data is used by MFx to calculate the delivered three dimensional dose (3D) based on the recorded machine state during the treatment. A gamma index of 3 mm/3 % was considered passing. If PD or MFx failed in any way, a MapCheck2 could be used for individual beam analysis.
Results: Sporadic failures of all three systems convinced us that both active (PD, MapCheck2) and passive (MFx) systems should be used at the same time in our clinic. One real MLC problem was uncovered by PD, while downtime for PD exceeded MFx due to QA system errors. Without redundancy, exclusive use of only one system would have resulted in delays while physics troubleshoots the single system.
Conclusion: Neither PD nor MFx will be used exclusively in clinic; both systems will be run in parallel.
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