Alternating-gradient canted cosine theta superconducting magnets for future compact proton gantries

Abstract

We present a design of superconducting magnets, optimized for application in a gantry for proton therapy. We have introduced a new magnet design concept, called an alternating-gradient canted cosine theta (AG-CCT) concept, which is compatible with an achromatic layout. This layout allows a large momentum acceptance. The 15 cm radius of the bore aperture enables the application of pencil beam scanning in front of the SC-magnet. The optical and dynamic performance of a gantry based on these magnets has been analyzed using the fields derived (via Biot-Savart law) from the actual windings of the AG-CCT combined with the full equations of motion. The results show that with appropriate higher order correction, a large 3D volume can be rapidly scanned with little beam shape distortion. A very big advantage is that all this can be done while keeping the AG-CCT fields fixed. This reduces the need for fast field ramping of the superconducting magnets between the successive beam energies used for the scanning in depth and it is important for medical application since this reduces the technical risk (e.g., a quench) associated with fast field changes in superconducting magnets. For proton gantries the corresponding superconducting magnet system holds promise of dramatic reduction in weight. For heavier ion gantries there may furthermore be a significant reduction in size.

New horizons in particle therapy systems

“…For this gantry, a set of Canted Cosine Theta (CCT) combined function magnets have been developed at the Lawrence Berkeley National Laboratory. 69 Another magnet design alternative based on the racetrack geometry has been designed at Paul Scherrer Institute. 70 The magnets are to be cooled with the cryo-coolers directly mounted on the cold mass.…”

Design of an Achromatic Superconducting Magnet for a Proton Therapy Gantry

“…A process has been developed to closely couple the magnet coil design to the desired beam optics [1]. This begins with the completion of an initial gantry optics design using the simulation code COSY Infinity [18].…”

“…This is a new concept, described in detail in [1], in which multiple CCT quadrupole winding sections are placed along the length of a bend such that the effective current is reversed between them. The alternation of the field along the length can be tuned by choosing the number and location of transitions between sections.…”

“…Recently, a new superconducting magnet concept called the Alternating Gradient Canted-Cosine-Theta (AG-CCT) was developed to make use of these advantages. A first design study implementing the AG-CCT concept was completed, achieving twenty-five percent momentum acceptance in a compact gantry for proton therapy [1]. Lawrence Berkeley National Laboratory (LBNL) in collaboration with the Paul Scherrer Institute (PSI) and Varian Medical Systems is now developing a superconducting magnet for a similar system.…”

“…This paper will share the most recent developments of this effort by reporting on the design of a curved AG-CCT superconducting magnet. The magnet is designed to transport protons of energy 70-220 MeV over the final 135 degrees of bending in a gantry similar to the system presented in [1]. The large momentum acceptance (Δp/p = 20%) allows for treatment using a range of energies without magnet field change.…”