ESTRO 2022

Session Item

Dosimetry

Session Code: 6034

Session Type: Poster (digital)

Track: Physics

Determination of field output correction factors for the IBA Razor Diode

Alexia Delbaere, France

Presentation Number: PO-1533

Abstract

Abstract Title:

Determination of field output correction factors for the IBA Razor Diode

Authors:

Alexia Delbaere^1,2, Nicolas Hammel², Oussama Saadi³, Luc Simon^1,2, Catherine Khamphan³, Laure Vieillevigne^1,2

¹Centre de Recherches en Cancérologie de Toulouse, UMR1037 INSERM - Université Toulouse 3 – ERL5294 CNRS, Toulouse, France; ²Institut Claudius Regaud – Institut Universitaire du Cancer de Toulouse, Medical Physics, Toulouse, France; ³Institut du Cancer – Avignon Provence, Medical Physics, Avignon, France

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Purpose or Objective

The IAEA TRS-483 reportprovides field output correction factors for relative dosimetry in small fields for detectors available before 2015. These factors must be updated when new detectors become available. This includes the IBA Razor diode for which limited data are published (1–3). Hence, the aim of this study was to determine its correction factors to complement and expand the available dataset.

Material and Methods

The correction factors were determined for a Varian TrueBeam linear accelerator for 6 WFF (With Flattening Filter), 6 FFF and 10 FFF (Flattening Filter Free) beams at 5 cm depth with a source-to-surface distance of 95 cm. Nominal field sizes (collimated with MLC) ranging from 5x5 mm² to 30x30 mm² were studied and the 100x100 mm² was taken as the msr field. Monte Carlo simulations were performed with GATE(v9.0)/Geant4(v10.6.patch01) using the phase space files from Varian and the Razor blueprint from IBA. For the experimental determination, Gafchromic EBT3 films were used as reference. Moreover, field output ratios (corrected with factors from IAEA TRS-483) were measured with the PTW T60019 microDiamond and were used as a third method to determine field output correction factors of the Razor diode.

Results

The Razor diode showed an over-response for the 5x5 mm² field size but fulfilled the 5% correction limit recommended by the IAEA TRS-483. Correction factors for the 10x10 mm² field size were 1.007, 1.017 and 0.998 for 6 WFF, 6 FFF and 10 FFF, respectively. Monte Carlo simulations showed comparable results to the measurements (EBT3 and T60019 microDiamond) and the literature except for the 5x5 mm². For the latter, the differences between Monte Carlo and experimental methods were around 2% and our correction factors ranged between the values published by Casar et al (2) and Gul et al (3).

Conclusion

The data provided in this work will contribute to an updated database for correction factors of the IBA Razor diode.

1. Poppinga D, Delfs B, Meyners J, Harder D, Poppe B, Looe HK. The output factor correction as function of the photon beam field size – direct measurement and calculation from the lateral dose response functions of gas-filled and solid detectors. Med Phys. 2017 Aug 1;28(3):224–35.

2. Casar B, Gershkevitsh E, Mendez I, Jurković S, Huq MS. A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams. Med Phys. 2019 Feb 1;46(2):944–63.

3. Gul A, Fukuda S, Mizuno H, Taku N, Kakakhel MB, Mirza SM. Feasibility study of using Stereotactic Field Diode for field output factors measurement and evaluating three new detectors for small field relative dosimetry of 6 and 10 MV photon beams. J Appl Clin Med Phys. 2020 Nov 1;21(11):23–36.