Abstract
Very high energy electrons (VHEE) in the range from 100 to 250MeV have the potential of becoming an alternative modality in radiotherapy because of their improved dosimetric properties compared with 6–20MV photons generated by clinical linear accelerators (LINACs). VHEE beams have characteristics unlike any other beams currently used for radiotherapy: femtosecond to picosecond duration electron bunches, which leads to very high dose per pulse, and energies that exceed that currently used in clinical applications. Dosimetry with conventional online detectors, such as ionization chambers or diodes, is a challenge due to non-negligible ion recombination effects taking place in the sensitive volumes of these detectors. FLUKA and Geant4 Monte Carlo (MC) codes have been employed to study the temporal and spectral evolution of ultrashort VHEE beams in a water phantom. These results are complemented by ion recombination measurements employing an IBA CC04 ionization chamber for a 165MeV VHEE beam. For comparison, ion recombination has also been measured using the same chamber with a conventional 20MeV electron beam. This work demonstrates that the IBA CC04 ionization chamber exhibits significant ion recombination and is therefore not suitable for dosimetry of ultrashort pulsed VHEE beams applying conventional correction factors. Further study is required to investigate the applicability of ion chambers in VHEE dosimetry.
Highlights
Scanning very high energy electron (VHEE) beams is an emerging modality that has potential of becoming a new cost effective [1] radiotherapy treatment technique, with further development of laser plasma accelerator technology [2]
The measurements with the CC04 chamber are recommended to be carried out at +300 V polarizing voltage
From the distribution of the time of flight of the electron beam, the bunch length duration has been estimated for various positions along the beam propagation path in air and water phantom
Summary
Scanning very high energy electron (VHEE) beams is an emerging modality that has potential of becoming a new cost effective [1] radiotherapy treatment technique, with further development of laser plasma accelerator technology [2]. The potential clinical advantage of electron beams with energies exceeding 100 MeV have been studied for lung cancer [9] and prostate cancer treatment [10]. These studies conclude that electron beams with energies above 100 MeV can achieve a very good dose conformation, comparable with, or even exceeding, those of current photon modalities, while offering significantly improved dose sparing of healthy tissue [11]. For the studied patient cases, VHEE dose to all critical organs was up to 70% lower than the clinical 6 MV VMAT dose [12]
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