ESTRO 37 Abstract book

ESTRO 37

S459

range of monoenergetic proton energies between 60 MeV and 230 MeV (with different beam diameters and calorimeter buildups), (2) for clinical SOBPs, such as the standard test volume recommended in the draft Code. Results For 3cm diameter monoenergetic beams with no additional calorimeter buildup (0.65 g/cm 2 water- equivalent (WE) inherent), k gap increases with energy up to 0.4% above unity at 230 MeV. By changing the total buildup to 2.0 g/cm 2 WE, k gap increases with energy up to 0.8% above unity at 230 MeV. However, increasing the beam diameter so that lateral charge particle equilibrium (LCPE) is achieved reduces k gap to within 0.1% of unity for all energies (and all buildups up 2.0 g/cm 2 WE). k vol was found to vary from -0.3% less than unity at 60 MeV to +0.3% above unity at 230 MeV with no significant change with increasing beam diameter or buildup. For the clinical SOBP recommended in the Code (10x10x10 cm 3 box field at 15 g/cm 2 WE depth), both k gap and k vol were found to be within 0.1% of unity. Conclusion The simulation results here indicate that k gap is close to unity for monoenergetic proton beams (and different amounts of buildup) when the beam diameter is large enough so that LCPE is achieved. k vol was found to be dependent on beam energy (changing by 0.6% between 60MeV and 230 MeV) but not significantly on the amount of buildup in front of the calorimeter. For the reference clinical SOBP, however, both correction factors are close to unity which is ideal for reference dosimetry. These results will significantly contribute to the establishment of the NPL graphite calorimeter as a primary standard in proton therapy. A. Bartoli 1 , M. Scaringella 2 , A. Baldi 3 , D. Greto 4 , S. Scoccianti 4 , L. Masi 5 , S. Pallotta 6 , M. Bruzzi 7 , C. Talamonti 6 1 Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, Florence, Italy 2 Università di Firenze, Dipartimento di Ingegneria dell’Informazione, Firenze, Italy 3 Università di Firenze, Dipartimento di Ingegneria Industriale, Florence, Italy 4 Azienda Ospedaliero Universitaria Careggi, Radiotherapy Unit, Florence, Italy 5 IFCA, Department of Medical Physics and Radiation Oncology, Florence, Italy 6 University of Florence, Biomedical Experimental and Clinical Science, Florence, Italy 7 University of Florence, Department of Physics and Astronomy, Florence, Italy Purpose or Objective Modern complex radiotherapy techniques, such as volumetric-modulated arc therapy (VMAT) and stereotactic body radiation therapy (SBRT), pose a number of challenges in properly measuring commissioning data and quality assurance radiation dose distributions. At present, pretreatment verification for each individual patient is performed using detectors which suffer from some drawback. Therefore novel devices coping with strict conditions are needed. This study aims at investigating the use of DIAPIX (DIAmond PIXel), a pixelated matrix of polycrystalline Chemical Vapour Deposition diamond detectors, for pre-treatment dose verifications. Due to its intrinsic characteristics this device could represent the best solution for pretreatment PO-0873 2D pixelated diamond detector for patient QA in advanced radiotherapy treatments

Conclusion We have developed a novel DDC phantom and dedicated analysis software that have shown to be useful in comparing the low contrast image quality of different CBCT image acquisition protocols and vendor solutions. PO-0872 Monte Carlo calculated correction factors for a proton calorimeter in clinical proton beams D. Shipley 1 , F. Romano 1 , H. Palmans 2 1 National Physical Laboratory, Medical Radiation Physics, Teddington, United Kingdom 2 EBG MedAustron GmbH, Medical Physics, A-2700 Wiener Neustadt, Austria Purpose or Objective Calorimetry is the only fundamental method for measuring the absorbed dose according to its definition. A calorimeter measures the temperature rise resulting from irradiation in an absorber (core), assuming all the energy deposited in a material appears as heat. Unlike other detectors (ionization chambers, Faraday cups), a calorimeter inherently provides a method to measure the energy deposited by radiation directly. The National Physical Laboratory (NPL) is currently commissioning a portable graphite calorimeter as a primary standard of absorbed dose to water for clinical proton beams with the aim of delivering an uncertainty on reference dosimetry for protons of around 2% (at 95% confidence level) based on a draft IPEM UK Code of Practice. In this work, key corrections required to obtain absorbed dose to graphite from a calorimeter measurement have been determined in a range of monoenergetic and clinical proton beams. Material and Methods A Monte Carlo application was developed with TOPAS (v3.1) based on Geant4 to determine the gap (k gap ) and volume averaging (k vol ) correction factors for the calorimeter. The former is related to the effect due to the presence of vacuum gaps within the calorimeter, the latter converts the mean absorbed dose in the graphite core to the absorbed dose in a point located at the centre of the core. k gap and k vol were determined (1) for a