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TU‐CD‐304‐08: Feasibility of a VMAT‐Based Spatially Fractionated Grid Therapy Technique
Author(s) -
Zhao B,
Jin J,
Liu M,
Huang Y,
Kim J,
Brown S,
Siddiqui F,
Chetty I,
Wen N
Publication year - 2015
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 - 10.1118/1.4925577
Subject(s) - imaging phantom , nuclear medicine , collimator , radiation treatment planning , radiation therapy , linear particle accelerator , dosimetry , physics , optics , biomedical engineering , medical physics , medicine , beam (structure) , radiology
Purpose: Grid therapy (GT) uses spatially modulated radiation doses to treat large tumors without significant toxicities. Incorporating 3D conformal‐RT or IMRT improved single‐field GT by reducing dose to normal tissues spatially through the use of multiple fields. The feasibility of a MLC‐based, inverse‐planned multi‐field GT technique has been demonstrated. Volumetric modulated arc therapy (VMAT) provides conformal dose distributions with the additional potential advantage of reduced treatment times. In this study, we characterize a new VMAT‐based GT (VMAT‐GT) technique with respect to its deliverability and dosimetric accuracy. Methods: A lattice of 5mm‐diameter spheres was created as the boost volume within a large treatment target. A simultaneous boost VMAT (RapidArc) plan with 8Gy to the target and 20Gy to the boost volume was generated using the Eclipse treatment planning system (AAA‐v11). The linac utilized HD120 MLC and 6MV flattening‐filter free beam. Four non‐coplanar arcs, with couch angles at 0, 45, 90 and 317° were used. Collimator angles were at 45 and 315°. The plan was mapped to a phantom. Calibrated Gafchromic EBT3 films were used to measure the delivered dose. Results: The VMAT plan generated a highly spatially modulated dose distribution in the target. D95%, D50%, D5% for the spheres and the targets in Gy were 18.9, 20.6, 23 and 8.0, 9.6, 14.8, respectively. D50% for a 1cm ring 1cm outside the target was 3.0Gy. The peak‐to‐valley ratio of this technique is comparable to previously proposed techniques, but the MUs were reduced by almost 50%. Film dosimetry showed good agreement between calculated and delivered dose, with an overall gamma passing rate of >98% (3% and 1mm). The point dose differences at sphere centers varied from 2–8%. Conclusion: The deliverability and dose calculation accuracy of the proposed VMAT‐GT technique demonstrates that ablative radiation doses are deliverable to large tumors safely and efficiently.