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Accelerators for Protons and Other Heavy Charged Particles
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Alejandro Mazal, Annalisa Patriarca
The extraction of the beam can be achieved by various methods. Electrostatic deflectors are often used in conventional cyclotrons. In a synchrocyclotron, electromagnetic channels cancel the main magnetic field and let the particles come out in a straight line. An electromagnet kicker can be used, particularly for synchrotrons. When negative ions are being accelerated, a different approach can be used. It is possible to strip off the electrons from the ions with a thin target once they have reached the desired energy. The resulting positive ions will emerge from the accelerating chamber with a curved trajectory opposite to that of the orbit of the negative ions.
ABC: Accelerators, Beams, and Charges
Published in Rob Appleby, Graeme Burt, James Clarke, Hywel Owen, The Science and Technology of Particle Accelerators, 2020
Rob Appleby, Graeme Burt, James Clarke, Hywel Owen
The synchrotron improves upon the synchrocyclotron by also varying the magnetic field with time; here, the path of the particles through the magnets is kept constant as the particle energy increases and the RF is matched to be where fr is the (orbital) revolution frequency and the harmonic number h is an integer. An illustration is given in Fig 2.9. The betatron – invented by Donald Kerst also in the 1930s – is similar in that it circulates charged particles (here electrons) at a constant radius, but uses induction acceleration via an e.m.f. generated as the magnetic field itself varies. Frank Goward and D. E. Barnes adapted a betatron to build the first synchrotron in 1946 at Woolwich (London) which accelerated 8 MeV electrons, and the following year an electron synchrotron at General Electric's laboratory demonstrated the production of synchrotron radiation (see Chapter 6). By maintaining a constant beam path that is independent of particle energy, the magnet sizes can be enormously reduced particularly at high energies enabling the very largest colliders such as the LHC to be produced with a realistic cost. The other great advance made around the same time (in 1949) was Nicholas Christofilos's strong-focusing principle, which allows the circulating beam size to be greatly reduced, making the magnets much smaller again; this is discussed later in Chapter 5.
Proton Accelerators
Published in Harald Paganetti, Proton Therapy Physics, 2018
The passive scattering technique is a robust technique with respect to timing issues in the proton beam. The only issue on timing is the range modulation. The rotation of the wheel causes energy changes at a frequency of a few hundred Hz. Processes occurring at this (or related) frequency may cause distortion in the dose application and measurement data. One should, for example, take care of intensity oscillations (pulses) from the accelerator or data read-out sequences at these frequencies. Especially, when using a synchrocyclotron, one should take care of such timing interferences.
Understanding the FLASH effect to unravel the potential of ultra-high dose rate irradiation
Published in International Journal of Radiation Biology, 2022
Houda Kacem, Aymeric Almeida, Nicolas Cherbuin, Marie-Catherine Vozenin
In addition to the benefits reported in late responding organs, UHDR irradiation was also beneficial in acute responding organs such as the gastrointestinal track and the hematopoietic system (see section ‘The FLASH effect validated in patient and human samples’, and Chabi et al. 2020). Intestinal function, epithelial integrity and regenerating crypts were preserved while DNA damage and apoptosis in the columnar cells of the crypt were reduced after exposure to 14 Gy at UHDR (216 Gy/s, electron). Again, anti-tumor efficacy in a preclinical mouse model of ovarian cancer (ID8) was comparable to that obtained with CONV-RT (0.08 Gy/s) (Levy et al. 2020). The beneficial effects of UHDR were again validated with proton and photon beams using pancreatic tumor models. The radiation-induced gastrointestinal syndrome did not occur upon UHDR irradiation using 18 Gy proton radiotherapy (UHDR-PRT) (Diffenderfer et al. 2020) and with 15 Gy X-rays (Gao et al. 2020) suggesting that the FLASH effect is relatively independent of the ionizing radiation modality. Recently, using GI as model, the FLASH effect was confirmed with spread-out Bragg peak irradiation. Using a pulsed synchrocyclotron, Evan et al. showed that mice irradiated at 10–16 Gy UHDR (96 Gy/s) exhibited enhanced survival with LD50 reaching 14.1 Gy with UHDR vs. 13.5 Gy with conventional dose rate (Evans et al. 2021). Consistently, Kim et al. study compares the outcome of the proton transmission at UHDR (UHDR-PRT transmission) vs. the spread-out Bragg peak (UHDR-PRT SOBP) in mouse intestine and pancreatic tumor control. Toxicity was significantly decreased in both configurations, i.e. 15 Gy UHDR-PRT SOBP (108.2 ± 8.3 Gy/s) vs. UHDR-PRT transmission (107.1 ± 15.2 Gy/s). In contrast, conventional dose rate proton transmission (CONV-PRT transmission, 0.83 ± 0.19 Gy/s) and SOBP (CONV-PRT SOBP, 0.82 ± 0.14 Gy/s) both generated important damages with reduced regenerating and proliferating crypts. Importantly, 18 Gy at UHDR and conventional dose rate irradiation were equipotent to control subcutaneous MH641905 mouse pancreatic tumors in both transmission and spread-out Bragg peak dose regions. All mice treated with CONV-PRT and UHDR-PRT transmission survived the treatment. In SOBP, 70% of the mice treated at conventional dose rate died 20 days after irradiation whereas UHDR induced only 15% of lethality (Kim et al. 2021). Ultimately, Ruan et al. also reported a decreased gastrointestinal toxicity and better crypt survival at UHDR (electron, 7.5–12.5 Gy, 2–6 × 106 Gy/s) with a relatively low dose-modifying factor of 1.1, in comparison to conventional dose rate (CONV, 0.25 Gy/s). The FLASH effect was lost when delivery time between two pulses and pulse repetition number were increased, highlighting the relevance of parameterization studies to define the FLASH effect (Ruan et al. 2021).