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SU‐E‐T‐327: Dosimetry and Implementation of High‐Dose Rate MLC‐Based GRID Therapy Using a 6MV Flattened Filter Free (FFF) Photon Beam
Author(s) -
Dou K,
Lerma F,
Jacobs M,
Li B
Publication year - 2013
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 - 10.1118/1.4814761
Subject(s) - truebeam , isocenter , multileaf collimator , collimator , dosimetry , linear particle accelerator , nuclear medicine , aperture (computer memory) , optics , beam (structure) , grid , radiation treatment planning , physics , materials science , radiation therapy , medicine , mathematics , radiology , geometry , acoustics , imaging phantom
Purpose: To dosimetrically characterize high‐dose rate multileaf collimator (MLC)‐based, spatially‐fractionated GRID therapy (MLC GRID) using a 6MV flattened filter free (FFF) photon beam delivered from a Varian TrueBeam linear accelerator. Methods: Planning for MLC GRID therapy was done by a Varian Eclipse treatment planning system. The dose plane at depth of 5cm was exported for a dose comparison between the calculated and measured data. MLC GRID with the projected square openings of 10 x 10 mm at the isocenter was studied using 6MV FFF photons at a dose rate of 1400MU/min. Four separate MLC‐shaped beams of each with two columns of GRID openings were automated for delivery by a Varian TrueBeam linear accelerator. MLC GRID was characterized with depth dose, profile and output using an IBA scanning system. Results: 6MV FFF GRID patterns recorded using films and EPID were found to be consistent in both aperture sizes and alignment. A MapCheck was used to validate the 16–20 cm field of a 6MV FFF GRID with a pass rate of 97% at 3%/3mm criteria. The ratio of the openings to the blocked area was quantified to be 25% with a valley–to–peak ratio of about 16.5% from the beam profiles in the central aperture. GRID therapy is a technique to treat advanced bulky tumor in a single or a few fractions by delivering a dose of 12 to 20Gy to tumors that do not respond to conventional fractionation schemes. Four abutting GRID fields with 3000 MU to each field took only about 9 minutes using a 6MV FFF beam, but took more than 30 minutes for delivery at 400 MU/min. Conclusion: 6MV FFF MLC–based GRID therapy aligned accurately with IGRT showed advantages in the higher dose delivery by more than 2 times reducing treatment time over a conventional delivery.