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SU‐E‐T‐517: Dosimetric Evaluation of Beam‐Hold Interruption in Respiratory Gated RapidArc Delivery
Author(s) -
Shen S,
Popple R,
Duan J,
Wu X,
Brezovich I
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612470
Subject(s) - duty cycle , nuclear medicine , ionization chamber , linear particle accelerator , imaging phantom , dosimetry , beam (structure) , arc (geometry) , medicine , biomedical engineering , optics , physics , ion , mathematics , power (physics) , geometry , ionization , quantum mechanics
Purpose: Varianˈs TureBeam linear accelerator delivers respiratory gated RapidArc treatment by beam‐hold until at right gantry position/speed and gated window. The current study evaluated the impact of beam‐hold interruption to gated RapidArc dose delivery. Method and Materials: Two delivery modes were examined: (1) Flattening Filter Free (FFF) mode with maximum dose rate of 2400 MU/min (2) standard delivery mode with maximum dose rate of 600 MU/min. An 1 arc plan for SBRT lung cancer in FFF mode (12 Gy/fraction) and a 2 arc plan for pancreatic cancer (1.8 Gy/frcation) were delivered to a phantom. Dosimetric differences between the gated and non‐gated deliveries were compared using film and ion chamber. Beam‐hold interruptions were tested for respiratory rate of 12, 15, 20, 30 cycle/min with a gating threshold of 33.3% duty cycle. Results: Beam‐hold interruption number ranged from 44 for the 1 arc plan at 12 cycle/min to 349 for the 2 arc plan at 30 cycle/min. 2 arc plan delivery time increased from 104 seconds for non‐gated to 768 seconds for gated at 30 cycle/min. Beam‐hold number increased more than twice when respiratory rate increased from 20 to 30 cycle/min. The difference between the gated and non‐gated ion chamber measurements was within 0.16% for 1 arc delivery in FFF mode and within 0.24% for 2 arc plan in standard mode. The difference between the gated and non‐gated film measurements ranged in 0–0.01% pixels for > 3%/3mm (0.03–0.46 for 2%/2mm) for 1 arc in FFF mode, and in 0.96–2.15% pixels for > 3%/3mm (6.03–12.65 for 2%/2mm) for 2 arc delivery in standard mode. There were no clear association between number of beam‐hold and dosimetric differences. Conclusion: In clinical respiratory rate range, gated RapidArc deliveries were in agreement with non‐gated RapidArc deliveries in both FFF mode and standard mode.