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Magnetically focused 70 MeV proton minibeams for preclinical experiments combining a tandem accelerator and a 3 GHz linear post‐accelerator
Author(s) -
Mayerhofer Michael,
Datzmann Gerd,
Degiovanni Alberto,
Dimov Veliko,
Dollinger Günther
Publication year - 2021
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.14854
Subject(s) - linear particle accelerator , van de graaff generator , physics , proton , nuclear physics , beam (structure) , particle accelerator , quadrupole , radio frequency quadrupole , proton therapy , bragg peak , quadrupole magnet , optics , atomic physics
Purpose Radiotherapy plays an important role for the treatment of tumor diseases in two‐thirds of all cases, but it is limited by side effects in the surrounding healthy tissue. Proton minibeam radiotherapy (pMBRT) is a promising option to widen the therapeutic window for tumor control at reduced side effects. An accelerator concept based on an existing tandem Van de Graaff accelerator and a linac enables the focusing of 70 MeV protons to form minibeams with a size of only 0.1 mm for a preclinical small animal irradiation facility, while avoiding the cost of an RFQ injector. Methods The tandem accelerator provides a 16 MeV proton beam with a beam brightness of B = 4 nA mm 2 mrad 2as averaged from 5 µs long pulses with a flat top current of 17 µA at 200 Hz repetition rate. Subsequently, the protons are accelerated to 70 MeV by a 3 GHz linear post‐accelerator consisting of two Side Coupled Drift Tube Linac (SCDTL) structures and four Coupled Cavity Linac (CCL) structures [design: AVO‐ADAM S.A (Geneva, Switzerland)]. A 3 GHz buncher and four magnetic quadrupole lenses are placed between the tandem and the post‐accelerator to maximize the transmission through the linac. A quadrupole triplet situated downstream of the linac structure focuses the protons into an area of (0.1 × 0.1) mm 2 . The beam dynamics of the facility is optimized using the particle optics code TRACE three‐dimensional (3D). Proton transmission through the facility is elaborated using the particle tracking code TRAVEL. Results A study about buncher amplitude and phase shift between buncher and linac is showing that 49% of all protons available from the tandem can be transported through the post‐accelerator. A mean beam current up to 19 nA is expected within an area of (0.1 × 0.1) mm 2 at the beam focus. Conclusion An extension of existing tandem accelerators by commercially available 3 GHz structures is able to deliver a proton minibeam that serves all requirements to obtain proton minibeams to perform preclinical minibeam irradiations as it would be the case for a complete commercial 3 GHz injector‐RFQ–linac combination. Due to the modularity of the linac structure, the irradiation facility can be extended to clinically relevant proton energies up to or above 200 MeV.