SHARP: A compact focusing system for medical applications using a diverging plasma lens

Abstract: Cancer therapy for deep-seated tumors requires precise irradiation of a small target deep within the patient while minimizing radiation exposure to surrounding tissues. This can be accomplished with a round beam sharply converging towards a single spot, requiring a large beam size in both planes at the exit of the focusing system. Achieving this over a short distance using only quadrupole lenses is challenging; but by using a linear active plasma lens (APL) in defocusing mode, the beam can be quickly and non-destructively enlarged before focusing using quadrupoles. The position of the irradiation spot can also be scanned in three dimensions by changing magnet settings. The SHARP project will develop and test this concept. Such a system can be used with very high energy electrons (hundreds of MeV), creating a Bragg-peak-like spot using novel accelerator technology. This could lead to more compact radiotherapy facilities, not requiring a bulky infrastructure typically associated with proton radiotherapy machines. If successful, SHARP will enable precision conformal radiotherapy, spatial fractionation, and potentially be useful for FLASH radiotherapy.