Diamond detectors as a powerful real-time tool for commissioning UHDR electron beams in water
Alessia Gasparini,
Belgium
OC-0283
Abstract
Diamond detectors as a powerful real-time tool for commissioning UHDR electron beams in water
Authors: Alessia Gasparini1,2, Giuseppe Felici3, Federica Galante3, Faustino Gomez4, Rafael Kranzer5, Giulia Mariani3, Marco Marinelli6, Matteo Pacitti7, Josè Paz-Martin4, Verdi Vanreusel2,8, Giuanluca Verona Rinati6, Dirk Verellen1,2
1Iridium Netwerk, Radiotherapy, Antwerp, Belgium; 2University of Antwerp, Faculty of Medicine and Health Sciences, Antwerp, Belgium; 3SIT, R&D, Aprilia, Italy; 4University of Santiago de Compostela, MOLECULAR IMAGING AND MEDICAL PHYSICS, Santiago de Compostela, Spain; 5PTW, R&D, Freiburg, Germany; 6University of Rome Tor Vergata, Industrial Engineering, Rome, Italy; 7SIT, R1D, Aprilia, Italy; 8SCK CEN, Research in dosimetric applications, Mol, Belgium
Show Affiliations
Hide Affiliations
Purpose or Objective
Ultra-high dose rate (UHDR) systems are currently extensively used for Flash RT in preclinical experiments. The commissioning of these systems is non-standard, yet of extreme importance for a correct comparison of preclinical results. Commercially available ion chambers (ICs) suffer from non-correctable saturation effects at UHDR , Front. Phys. 2020) and most commissioning procedures are based on passive dosimeters, such as Gafchromic films and alanine Jaccard, Med. Phys. 2017, Montay-Gruel, Radiother. Oncol. 2017, Jorge, Radiother. Onc., 2019).
Here we report the use of a novel diamond based Schottky diode detector (fDiamond) for real-time, in water tank commissioning of a dedicated preclinical UHDR system (ElectronFlash SIT, Italy)).
Material and Methods
fDiamond is a diamond detector based on the microDiamond (mD, PTW, Germany) and successfully re-designed for UHDR by changing both the size of the active volume and the boron concentration in the diamond doped layer. For measurements in UHDR a PTW Tandem electrometer and an external box were provided by PTW, to avoid detector instantaneous currents exceeding the specifications of the electrometer.
Measurements were performed at 7 and 9 MeV with different applicators ranging from 10 to 120 mm2. The instantaneous dose rate (DR) and the dose per pulse (DPP) were up to 3 MGy/s and 13 Gy/pulse, respectively. All measurements were performed in a modified MP3-XS water tank using the MEPHYSTO mc2 software (PTW, Germany).
Absolute dosimetry is performed in reference conditions, using the 100 mm2 applicator, placing the water tank in contact with the applicator at 106 cm from the linac exit window and with the detector at dmax. For relative dosimetry an out-of-field PTW Advanced Markus electron chamber was used as reference chamber.
Absolute and relative dosimetry were performed by installing the fDiamond in the water tank using the same holder as the mD. The 3D movement of the water tank is controlled from the console room.
Results
Our results confirm that fDiamond can accurately measure dose up to at least 13 Gy/pulse. Response is linear with DPP within 5%. PDD were in less than one minute and compare well with the films (within 1 mm for R50 and 10 % overal, where the film uncertainty plays the largest role). Accurate positioning of the detector in the central field axis is performed via the software, more easily than with passive dosimeters.
Conclusion
fDiamond is a potential game changer for commissioning of UHDR system for Flash RT, as it allows dose measurements up to at least 13 Gy/pulse. It is able to measure real-time PDD and profiles in a water tank with accurate positioning using the PTW clinical software and potentially up to DPP of 26 Gy.
This work is part of the 18HLT04 UHDpulse project which received funding from the EMPIR programme.