ESTRO 37 Abstract book

S935

ESTRO 37

7 STUK, Radiation Dosimetry, Helsinki, Finland 8 IST-ID, Instituto Tecnológico e Nuclear, Lisboa, Portugal 9 Technische Hochschule Mittelhessen, Institute of Medical Physics, Giessen, Germany Purpose or Objective The IAEA TRS-398 ‘Absorbed Dose Determination in External Beam Radiotherapy’, the leading Code of Practice (CoP) in Europe for absorbed dose determination in external beam radiotherapy, is now being updated to incorporate the latest developments in currently available ionization chambers, treatment modalities, and their associated data. The objective of the EMPIR 16NRM03 RTNORM project is to contribute towards this update by both measuring and calculating k Q,Q0 factors for medium energy x-rays, conventional filtered (cFF) and flattening filter free (FFF) MV photons, and scanned proton beam modalities. Material and Methods A central aspect of the RTNORM project is that experimental determinations and Monte Carlo calculations of k Q,Q0 factors are cross-validated internally in the project consortium prior to the submission of a consistent dataset to the IAEA Task Group for the update of the IAEA TRS-398. The RTNORM project aims at contributing towards this update by addressing the following objectives: 1. kV x-ray beams between 100 kV and 250 kV, targeting k Q,Q0 factors with a target standard uncertainty better than 1.0 %. 2. High-energy (MV) photon beams between 4 MV and 20 MV, including conventional flattening filter (cFF) and flattening filter free beams (FFF), targeting k Q,Q0 factors with a target standard uncertainty better than 0.7 %. Scanned proton beams between 60 MeV and 250 MeV, targeting k Q,Q0 factors with a target standard uncertainty better than 2.0 %. 3.

This is achieved by (i) measurement of k Q,Q0 factors for a number of commonly used ion chambers and beam qualities in Europe, in all cases ensuring direct traceability of the measurements leading to the k Q,Q0 factors to primary standards of absorbed dose to water available in Europe; (ii) to calculate k Q,Q0 factors for these beams using several validated Monte Carlo codes; (iii) to compare the measured and calculated k Q,Q0 factors for all beam qualities and modalities. In case of medium energy x-rays a comparison will be made to compare the new absorbed dose-to- water based formalism using k Q,Q0 with a traditional air-kerma based formalism.

Conclusion The Stealth design makes it easy to use as a reference detector and it does not need repositioning with changing field sizes. The Stealth does not show any noticeable variation in the beam characteristics up to 20x20 cm 2 . Some variations are observed in PDDs and profiles for larger field sizes. For larger field sizes the Stealth can be used for relative measurements for QA purposes but its use for beam data acquisition or beam data validation is best limited up to 20x20 cm 2 for PDDs and 30x30 cm 2 for profiles. EP-1744 The EMPIR RTNORM Research Project contribution to the update of the IAEA TRS-398 Code of Practice M. Pinto 1 , C.E. Andersen 2 , F. Delaunay 3 , L. De Prez 4 , M. Donois 3 , S. Duane 5 , C. Gomà 6 , A. Kosunen 7 , J. Ojala 7 , M. Pimpinella 1 , B. Rapp 3 , T. Siiskonen 7 , L. Sommier 3 , P. Teles 8 , K. Zinc 9 1 ENEA-INMRI, Radiation Dosimetry, Santa Maria di Galeria Roma, Italy 2 DTU, Radiation Dosimetry, Roskilde, Denmark 3 LNE-LNHB, Radiation Dosimetry, Gif-Sur-Yvette, France 4 VSL, Ionizing Radiation Standards, Delft, The Netherlands 5 NPL, Radiation Dosimetry, Teddington, United Kingdom 6 KU Leuven, Department of Oncology - Laboratory of Experimental Radiotherapy, Leuven, Belgium

Results The project began in May 2017 and the earliest results include internal validation of Monte Carlo simulations in reference geometric conditions. Results of k Q,Q0 factors for the various modalities will be presented both from experiments and from Monte Carlo-calculations . Conclusion The cooperation of European national metrology institutes and research partners with industry in the EMPIR RTNORM project provides for a unique potential to join knowledge in order to provide essential and consistent datasets to be used by the European radiotherapy community. The RTNORM project is ongoing and results are being provided to TRS-398 revision task group on a regular basis.