Author: Kaile Li, Esmail Parsai 👨🔬
Affiliation: Alexander T. Augusta Military Medical Center, Alexander T. Augusta Miliary Medical Center 🌍
Purpose: To evaluate the sensitivity of the portal dosimetry system with the Arc CHECK system at identical Volumetric Modulated Arc Therapy (VMAT) setup
Methods: An Arc CHECK system from Sun Nuclear company was used as patient, the Arc CHECK system has two insets which are the inner plug at center of the phantom, and the large water equivalent outer plugs. Three scenarios were generated with all plugs inserted, chamber holder plug being out, and no plugs being insert to the ARC check system. Then a VMAT plan from a bladder patient was delivered to the ARC Check system and both of system were used to record the delivery dose, and the plan recorded doses were analyzed with Sun Nuclear patient software and Portal Dosimetry system from Varian Medical System. The evacuation parameter gamma included different distance to agreement( DTA), dose difference, and resolution comparison.
Results: For the three scenarios generated in this study, the selected two arc VMAT fields dose delivery recorded fluence map comparison in permutational combination sequence with gamma setting of 2% dose difference and 2mm DTA, the gamma less than 1 values were 95.5%, and 95.20%; 70.80% and 71.3%; and 71.90% and 72.90%. For the Arc CHECK System, the pass rate for gamma less than 1 at combined two recorded field fluences were 97.70%, 96.40%, and 64.10% for gamma setting at 3% dose difference and 3mm DTA.
Conclusion: The study evaluated Portal Dosimetry system sensitivity through employed a fixed structure of Arc CHECK system to simulate the unfixed patient treatment. The sensitivity of the cavity variation showed the portal dosimetry performance. And portal dosimetry is a plausible tool in recording of real time variation due to patient treatment target variation beside as a replacement of traditional VMAT QA tools with high efficiency and provides more clinical information.