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  • Comparison between TG-51 and TRS-398: electron contamination effect on photon beam-quality specification.

Comparison between TG-51 and TRS-398: electron contamination effect on photon beam-quality specification.

Physics in medicine and biology (2004-02-20)
Antonio Lopez Medina, Antonio Teijeiro, Francisco Salvador, Daniela Medal, Julio Vazquez, Manuel Salgado, María C Carrion
ABSTRACT

Two dosimetry protocols based on absorbed dose to water have recently been implemented: TG-51 and TRS-398. These protocols use different beam-quality indices: %dd(10)x and TPR20,10. The effect of electron contamination in measurements of %dd(10)x has been proposed as a disadvantage of the TG-51. For actual measurements of %dd(10)x in five clinical beams (Primus 6-18 MV, SL-75/5 6 MV, SL-18 6-15 MV) a purging magnet was employed to remove the electron contamination. Also, %dd(10)x was measured in the different ways described in TG-51 for high-energy beams: with a lead foil at 50 cm from the phantom surface, at 30 cm, and for open beam. Moreover, TPR20,10 was determined. Also, periodic quality-control measurements were used for comparing both quality indices and variation over time, but D20,10 was used instead of TPR20,10 and measurements in open beam for the %dd(10)x determination. Considering both protocols, S(w,air) and kQ were calculated in order to compare the results with the experimental data. Significant differences (0.3% for kQ) were only found for the two high-energy beams, but when the electron contamination is underestimated by TG-51, the difference in kQ is lower. Differences in the other cases and variations over time were less than 0.1%.

MATERIALS
Product Number
Brand
Product Description

Lead, foil, 10mm disks, thickness 0.5mm, as rolled, 99.99+%
Lead, foil, 15mm disks, thickness 0.01mm, 99.99+%
Lead, foil, 10mm disks, thickness 0.03mm, 99.99+%
Lead, foil, 25mm disks, thickness 0.15mm, as rolled, 99.95%
Lead, foil, 4mm disks, thickness 0.009mm, 99.99+%
Lead, foil, not light tested, 50x50mm, thickness 0.004mm, 99.99+%
Lead, foil, 4mm disks, thickness 0.025mm, 99.99+%
Lead, foil, light tested, 50x50mm, thickness 0.015mm, 99.99+%
Lead, foil, light tested, 50x50mm, thickness 0.0125mm, 99.99+%
Lead, foil, 8mm disks, thickness 0.15mm, as rolled, 99.95%
Lead, foil, 50x50mm, thickness 0.125mm, as rolled, 99.99+%
Lead, foil, 0.5m coil, thickness 0.25mm, as rolled, 99.95%
Lead, foil, 25x25mm, thickness 0.25mm, as rolled, 99.99+%
Lead, foil, 10mm disks, thickness 0.15mm, as rolled, 99.95%
Lead, foil, 1m coil, thickness 0.05mm, as rolled, 97% (sn 1.5%, sb 1.5%)
Lead, foil, light tested, 100x100mm, thickness 0.05mm, as rolled, 97% (Sn 1.5%, Sb 1.5%)
Lead, foil, 10mm disks, thickness 0.025mm, 99.99+%
Lead, foil, 15mm disks, thickness 0.15mm, as rolled, 99.95%
Lead, foil, 15mm disks, thickness 0.008mm, 99.99+%
Lead, foil, 100x100mm, thickness 1.0mm, as rolled, 99.5%
Lead, foil, 4mm disks, thickness 0.5mm, as rolled, 99.99+%
Lead, foil, 4mm disks, thickness 0.55mm, as rolled, 100%
Lead, foil, 300x300mm, thickness 0.15mm, as rolled, 99.95%
Lead, foil, 1m coil, thickness 0.125mm, as rolled, 99.95%
Lead, foil, 50x50mm, thickness 2.7mm, as rolled, 99.95%
Lead, foil, 15mm disks, thickness 0.04mm, 99.99+%
Lead, foil, 0.5m coil, thickness 1.0mm, as rolled, 99.5%
Lead, foil, 6mm disks, thickness 0.006mm, 99.99+%
Lead, foil, 6mm disks, thickness 0.5mm, as rolled, 99.95%
Lead, foil, 100x100mm, thickness 3.0mm, as rolled, 99.99+%