TU-CD-304-08: Feasibility of a VMAT-Based Spatially Fractionated Grid Therapy Technique
- Henry Ford Health System, Detroit, MI (United States)
- Georgia Regents University, Augusta, GA (Georgia)
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.
- OSTI ID:
- 22563044
- Journal Information:
- Medical Physics, Vol. 42, Issue 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
- Country of Publication:
- United States
- Language:
- English
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