Towards MR-guided electron therapy: Measurement and simulation of clinical electron beams in magnetic fields
© 2020 Associazione Italiana di Fisica Medica Purpose: In the current era of MRI-linac radiotherapy, dose optimization with arbitrary dose distributions is a reality. For the first time, we present new and targeted experiments and modeling to aid in evaluating the potential dose improvements offered with an electron beam mode during MRI-linac radiotherapy. Methods: Small collimated (1 cm diameter and 1.5 × 1.5 cm2 square) electron beams (6, 12 and 20 MeV) from a clinical linear accelerator (Varian Clinac 2100C) are incident perpendicular and parallel to the strong and localized magnetic fields (0–0.7 T) generated by a permanent magnet device. Gafchromic EBT3 film is placed inside a slab phantom to measure two-dimensional dose distributions. A benchmarked and comprehensive Monte Carlo model (Geant4) is established to directly compare with experiments. Results: With perpendicular fields a 5% narrowing of the beam FWHM and a 10 mm reduction in the 15% isodose penetration is seen for the 20 MeV beam. In the inline setup the penumbral width is reduced by up to 20%, and a local central dose enhancement of 100% is observed. Monte Carlo simulations are in agreement with the measured dose distributions (2% or 2 mm). Conclusion: A new range of experiments have been performed to offer insight into how an electron beam mode could offer additional choices in MRI-linac radiotherapy. The work extends on historic studies to bring a successful unified experimental and Monte Carlo modeling approach for studying small field electron beam dosimetry inside magnetic fields. The results suggest further work, particularly on the inline magnetic field scenario.
Kueng, R., Oborn, B., Roberts, N., Causer, T., Stampanoni, M., Manser, P., Keall, P. & Fix, M. (2020). Towards MR-guided electron therapy: Measurement and simulation of clinical electron beams in magnetic fields. Physica Medica: an international journal devoted to the applications of physics to medicine and biology, 78 83-92.