Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

© 2020 The Author(s). Published by IOP Publishing Ltd. Purpose: To identify the relative positions of the ultimate RBE, at a LET value of LETU (where the LET-RBE turnover point occurs independently of dose), and of the maximum LET (LETM) for a range of ions from protons to Iron ions. Methods: For a range of relativistic velocities (β), the kinetic energies, LET values and ranges for each ion are obtained using SRIM software. For protons and helium ions, the LET changes with β are plotted and LETM is compared with LETU. For all the ions studied the residual ranges of particles at LETU and LETM are subtracted to provide the physical separation (S) between LETU and LETM. Results: Graphical methods are used to show the above parameters for protons and helium ions. For all the ions studied, LETU occurs at kinetic energies which are higher than those at LETM, so the ultimate maximal RBE occurs proximal to the Bragg peak for individual particles and not beyond it, as is commonly supposed. The distance S, between LETU and LETM, appears to increase linearly with the atomic charge value Z. Conclusions: For the lighter elements, from protons to carbon ions, S is sufficiently small (less than the tolerance/accuracy of radiation treatments) and so will probably not influence therapeutic decisions or outcomes. For higher Z numbers such as Argon and Iron, larger S values of several centimetres occur, which may have implications not only in any proposed therapeutic beams but also at very low doses encountered in radiation protection where the few cells that are irradiated will typically be traversed by a single particle.

Original publication




Journal article


Biomedical Physics and Engineering Express

Publication Date