Shielding design for a laser-accelerated proton therapy system

Abstract

In this paper, we present the shielding analysis to determine the necessary neutron and photon shielding for a laser-accelerated proton therapy system. Laser-accelerated protons coming out of a solid high-density target have broad energy and angular spectra leading to dose distributions that cannot be directly used for therapeutic applications. A special particle selection and collimation device is needed to generate desired proton beams for energy- and intensity-modulated proton therapy. A great number of unwanted protons and even more electrons as a side-product of laser acceleration have to be stopped by collimation devices and shielding walls, posing a challenge in radiation shielding. Parameters of primary particles resulting from the laser-target interaction have been investigated by particle-in-cell simulations, which predicted energy spectra with 300 MeV maximum energy for protons and 270 MeV for electrons at a laser intensity of 2 x 10(21) W cm(-2). Monte Carlo simulations using FLUKA have been performed to design the collimators and shielding walls inside the treatment gantry, which consist of stainless steel, tungsten, polyethylene and lead. A composite primary collimator was designed to effectively reduce high-energy neutron production since their highly penetrating nature makes shielding very difficult. The necessary shielding for the treatment gantry was carefully studied to meet the criteria of head leakage <0.1% of therapeutic absorbed dose. A layer of polyethylene enclosing the whole particle selection and collimation device was used to shield neutrons and an outer layer of lead was used to reduce photon dose from neutron capture and electron bremsstrahlung. It is shown that the two-layer shielding design with 10-12 cm thick polyethylene and 4 cm thick lead can effectively absorb the unwanted particles to meet the shielding requirements.

Towards Laser Driven Hadron Cancer Radiotherapy: A Review of Progress

“…The shielding design for a laser-accelerated proton therapy system has been assessed by Fan et al [74]. Monte Carlo simulations determined the shielding necessary for 300 MeV protons and 270 MeV electrons at a laser intensity of 2 × 10 21 W·cm −2 .…”

A compact solution for ion beam therapy with laser accelerated protons

“…Such proposed schemes were based on a compact beamline with a primary collimator in front of a magnetic chicane filter [19,48]. Due to the very small opening angle (0.6°) of the primary collimator, used to limit diverging LAP bunches, such beamline uses a mere of *0.02 % of all protons in a bunch for dose delivery [50], while depositing huge numbers of protons in beam dumps and producing a high level of secondary (background) radiations. Such collimator-based beamlines are highly inefficient [51] reducing the per bunch dose.…”

Assessment of secondary radiation and radiation protection in laser-driven proton therapy

“…[7]) and novel concepts are being developed to overcome this limitation [8]. The assumed initial energy spectrum of the protons used here is very broad (with energies up to 300 MeV) and derived by extrapolating current experimental spectra to higher energies (as done in [9] and [8]). This is based on the target normal sheath acceleration (TNSA) mechanism [10] or other acceleration regimes that show broad energy spectra (e.g.…”