ESTRO 2022 - Abstract Book

S1313

Abstract book

ESTRO 2022

Conclusion We are the first to report a full characterisation of the new orthochromic film dosimetry system for radiotherapy, including an example treatment plan verification. The data provided is valuable for implementation of the system in a radiotherapy clinic or for dosimetric audits.

PO-1533 Determination of field output correction factors for the IBA Razor Diode

A. Delbaere 1,2 , N. Hammel 2 , O. Saadi 3 , L. Simon 1,2 , C. Khamphan 3 , L. Vieillevigne 1,2

1 Centre de Recherches en Cancérologie de Toulouse, UMR1037 INSERM - Université Toulouse 3 – ERL5294 CNRS, Toulouse, France; 2 Institut Claudius Regaud – Institut Universitaire du Cancer de Toulouse, Medical Physics, Toulouse, France; 3 Institut du Cancer – Avignon Provence, Medical Physics, Avignon, France Purpose or Objective The IAEA TRS-483 report provides 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. Materials 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 mm ² to 30x30 mm ² were studied and the 100x100 mm ² 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 mm ² field size but fulfilled the 5% correction limit recommended by the IAEA TRS-483. Correction factors for the 10x10 mm ² 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 mm ² . 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.