Room: Exhibit Hall | Forum 7
Purpose: Dynamic Arc delivery utilizes constantly simultaneous modulation of multileaf collimator(MLC), jaws, Gantry and Dose Rate(DR) . An in-house developed emulator to minimize treatment delivery time was used to assess difference in prostate treatments planned using three fractionation schemes. The emulator was designed for Elekta Synergy Linacs accelerators with Continuously Variable Dose Rate(CVDR)
Methods: Four prostate plans were optimized using three different fractionation schemes, namely A:40 Gy/5fractions(2 Arcs) , B: 62Gy/20fractions, C: 78Gy/34 fractions. The emulator was used to extract max-Gantry speed, max-MLC leaf speed, mean MLC leaf speed, DR as a function of control points. It was also used to extract a histogram of mean leaf separation, mean segment area and maximum MLC leaf motion. Independently, dose rate variation was assessed based on delivery of two plans optimized on a numerically simulated spherical phantom .
Results: All prostate plans had the same pattern of MU delivery, Gantry speed and DR variation. However, the number of segments delivering low MU, and variation in DR was maximized for the Plans 'C'. The histogram of mean MLC leaf separation was peaked at 1.5 cm for standard fractionation and at 0.5 cm for Plans 'A'. The DR comparison between emulator and real delivery for the phantom showed that latency for ramp-up and ramp-down in DR has a significant effect on delivery.The gammapass rate (3%,3mm) for plans 'A','B' and 'C' were approximately 97% , 95, 94% respectively .
Conclusion: From our study, we observe that Mean leaf separation, and DR variation play an important role in deliverability of a VMAT plan. The effect of MLC speed and Gantry speed needs to be assessed with control point analysis of the delivered QA plans. It is vital to account for the machine delivery parameters for DR and mean segment area/leaf separation during plan optimization