Surface Dose Investigation of the Flattening Filter-Free Photon Beams
- Radiation Oncology, Winship Cancer Center, Emory University, Atlanta, GA (United States)
- Melbourne Cancer Center, Melbourne, FL (Australia)
Purpose: Flattening filter-free (FFF) x-rays can provide more efficient use of photons and a significant increase of dose rate compared with conventional flattened x-rays, features that are especially beneficial for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). The available data on the entrance doses of the FFF photon beams remain limited. The purpose of this study was to investigate the entrance dose of FFF photons in the buildup region and to compare it with that of conventional flattened photons. Methods and Materials: A Varian TrueBeam linear accelerator has been in full clinical operation with 6-MV and 10-MV FFF and flattened x-ray photons. Entrance dose at the surface was measured using a parallel plate ionization chamber in a solid water phantom with buildup depth = 0{approx}15 mm for 6X and 0{approx}25 mm for 10X. Different field size (FS) patterns were created in the Eclipse Treatment Planning System by multileaf collimator (MLC) rather than jaws (FS = 2 Multiplication-Sign 2, 3 Multiplication-Sign 3, 4 Multiplication-Sign 4, 6 Multiplication-Sign 6, and 10 Multiplication-Sign 10 cm{sup 2} by MLC and jaw size = 2.2 Multiplication-Sign 2.2, 3.2 Multiplication-Sign 3.2, 4.2 Multiplication-Sign 4.2, 6 Multiplication-Sign 6, and 10 Multiplication-Sign 10 cm{sup 2}). The smallest FS was about four times larger than the ion chamber dimension. All buildup dose measurements were normalized to FS = 10 Multiplication-Sign 10 cm{sup 2} at the depth of dose maximum (dmax). Results: Good repeatability was demonstrated and surface dose increased linearly with FS for both flattened and FFF photons. The entrance dose of the FFF photons was modestly larger than that of the corresponding flattened photons for both 6X and 10X for different FS ranging from 2 Multiplication-Sign 2 cm{sup 2} to 10 Multiplication-Sign 10 cm{sup 2}. Conclusions: The FFF photons have a higher entrance dose than that of the corresponding flattened photons for FS smaller than 10 Multiplication-Sign 10 cm{sup 2}. However, the difference is not substantial and may be clinically insignificant.
- OSTI ID:
- 22056427
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 83, Issue 2; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
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