CCRI Webinar - 12/09/2023 - Small field dosimetry for MR guided radiotherapy

MR guided radiotherapy (MRgRT) based on MR-linacs has been introduced into the clinics and its dosimetry in reference conditions, for conventional field size of 10 x 10 cm2, has been established. Although the field size in such conditions establishes equilibrium conditions, they are far from being representative of clinical beams. Small radiation fields, typically smaller than 4 x 4 cm², are the main ingredients for optimising clinical treatments. Standardised protocols for small field dosimetry exists, e.g. IAEA TRS-483. However MR-linac dosimetry, which is performed in the presence of magnetic fields, is not accounted for in TRS-483. Therefore, there is a strong need to develop a measurement methodology for small fields in MRgRT to support dosimetry protocols. This will assure optimal treatment outcomes and patient safety.

The aim of this webinar is to present results from the MRgRT-DOS project (https://mrgrtmetrology.com/), funded by the European Metrology Program for Innovation and Research (EMPIR), that will enable the extension of the TRS 483 dosimetry protocol to support small field dosimetry in MRgRT. This includes the investigation on the influence of the magnetic field on the radiation field characteristics, on detector characteristics relevant for small field dosimetry, and the determination of detector type specific output correction factors for MRgRT.

00:00:00 Introduction – Jacco de Pooter (VSL)
00:01:14 Overview of MRI linac technology - Sonja Surla (DKFZ)
00:11:48 Detector characteristics - 1: effective point of measurement - Hui Khee Looe (Uni. of Oldenburg)
00:23:51 Detector characteristics - 2: fluence perturbation effects and volume averaging - Yunuen Cervantes (Université Laval)
00:36:02 Extending TRS-483 to small fields in MRgRT – Ralf-Peter Kapsch (PTB)
00:56:08 Monte Carlo simulations of detector type specific output correction factors in the presence of magnetic field in experimental facilities using EGSnrs – Ilias Billas (NPL)
01:13:41 Monte Carlo simulations of detector type specific output correction factors in the presence of magnetic field in MRI linacs using Penelope – Jacco de Pooter (VSL)
01:28:15 Possibilities and limitations of experimental facilities – Stephan Frick (PTB)
01:40:16 Performance of scintillators in presence of magnetic fields – Claus Andersen (DTU)