Status of the Development of a Novel Compact Proton Therapy Gantry System Based on Pulsed Magnets for Laser-driven Beams

Purpose/Objective(s):

Proton acceleration on m scale via high intensity laser has become a compelling alternative to conventional accelerators and gained interests for its potential to reduce size and costs for proton therapy (PT) facilities. Next generation petawatt lasers promise laser-driven protons (LDP) with therapeutic energies. But, in contrast to conventionally accelerated quasi-continuous mono-energetic pencil beams with about 30 Gy/sec dose rate, LDP beams have diverse properties, i.e. ultra-intense pico-sec bunches with up to 1010 Gy/sec dose rate, large energy spread and divergence, and with only up to 10 Hz repetition rate. These properties make it challenging to adapt LDP beams directly for medical applications. The presented work is an ongoing joint translational research project of several institutions aiming to establish laser-driven PT. We will present the recent progress in design concepts and the status of the development.

Materials/Methods:

In addition to laser accelerator development, LDP beams demand radiobiological characterization and new solutions for beam transport and dose delivery. Laser-based technology for low energy LDP beams has been established for cell and small animal irradiation using a fixed beamline and is being utilized for systematic extreme dose rate radiobiological studies. For translation towards patient irradiation a highly compact 360° isocentric proton gantry system was designed based on light-weight iron-less high-field pulsed magnets. The gantry is integrated with beam control, energy selection and a novel dose delivery system, capable to magnetically control the beam spot size and to scan the beam for advanced irradiation schemes. A 3D TPS has been adapted and used to demonstrate clinical functionality of our system. For its realization, key high-field pulsed magnets are being developed.

Results:

Radiobiologically, so far no overall difference is observed for laser-driven ultra-high dose rates compared to conventional PT beams. Our double achromatic gantry system is about 3 times smaller than conventional PT gantries. The new dose delivery system can simultaneously widens the beam size (Ø 1-20 cm) and scan 10x20 cm2 field size, for the most efficient dose delivery. High quality clinical treatment plans can be provided with such beams. For the gantry realization a pulsed 40 T solenoid for particle capture and a 10 T compact iron-less 50° sector magnet were successfully tested. A pulsed 120 T/m gradient quadrupole is being manufactured.
Conclusions:
Our compact, light-weight gantry could provide an optimized solution for the laser-driven PT. The tests of pulsed gantry magnets are being continued. Our new conventional PT facility is additionally equipped with a petawatt laser laboratory and an experimental bunker. This will allow testing for clinical applicability of LDP systems side-by-side with conventional therapeutic proton beams as reference.

Acknowledgment:

This project was supported by German BMBF grant (03Z1N511 and 03Z1O511).