Dosimetry and spectral analysis of a radiobiological experiment using laser-driven proton beams

Abstract

Abstract. Laser-driven proton and ion acceleration is an area of increasing research interest given the recent development of short pulse-high intensity lasers. Several groups have reported experiments to understand whether a laser-driven beam can be applied for radiobiological purposes and in each of these the method to obtain dose and spectral analysis was slightly different. The difficulty with these studies is that the very large instantaneous dose rate is a challenge for commonly used dosimetry techniques, so that other more sophisticated procedures need to be explored. This article aims to explain a method for obtaining the energetic spectrum and the dose of a laser-driven proton beam irradiating a cell dish used for radiobiology studies. The procedure includes the use of a magnet to have charge and energy separation of the laser driven beam, Gafchromic films to have information on dose and partially on energy, and a Monte Carlo code to expand the measured data in order to obtain specific details of the proton spectrum on the cells. Two specific correction factors have to be calculated: one to take in account the variation of dose response of the films as a function of the proton energy and the other to obtain the dose to the cell layer starting from the dose measured on the films. This method, particularly suited to irradiation delivered in a single laser shot, can be applied in any other radiobiological experiment performed with laser driven proton beams, with the only condition that the initial proton spectrum has to be at least roughly known.The method was tested in an experiment conducted at Queen's University of Belfast using the TARANIS laser, where the mean energy of the protons crossing the cells was between 0.9 and 5 MeV, the instantaneous dose rate was estimated to be close to 10 9 Gy/s and doses between 0.8-5 Gy were delivered to the cells in a single laser shot. The combination of the applied corrections modified the initial estimate of dose by up to 40% Dosimetry and spectral analysis of a radiobiological experiment using laser-driven proton beams2

A phenomenological relative biological effectiveness (RBE) model for proton therapy based on all publishedin vitrocell survival data

“…Data removed due to the restriction of (α/β) x < 30 Gy included all the reported measurements in some studies (Ristic-Fira et al 2011, Petrović et al 2010, Antoccia et al 2009, Sakamoto et al 1980, Keta et al 2014) or the removal of selected data points (Belli et al 2000, Bettega et al 2000, Blomquist et al 1993, Grosse et al 2014, Baggio et al 2002, Schettino et al 2001, Urano et al 1980). The restriction of LET d < 20 keV/μm excluded another two studies (Goodhead et al 1992, Wéra et al 2011) as well as selected data points from other studies (Belli et al 1989, 1992, 1993, 1998, 2000, Bettega et al 1998, Chaudhary et al 2014, Fiorini et al 2011, Folkard et al 1989, Ogheri et al 1997, Prise et al 1990, Schettino et al 2001, Schuff et al 2002, Sgura et al 2000). The RBE was considered for proton doses ranging from 1 – 10 Gy, governed by the assumed validity of the linear-quadratic model.…”

Biological effectiveness on live cells of laser driven protons at dose rates exceeding 109 Gy/s

“…Further details of the dosimetric procedure and of method employed to reconstruct the proton spectrum incident onto the cells can be found in Ref. 17. These energy characteristics result in a few ns duration of the proton bunch impacting on the cells.…”

Experimental observation of transverse modulations in laser-driven proton beams

“…the source. Application experiments presently performed with laser-accelerated protons such as proton radiography [3][4][5][6] or radiobiological studies [7][8][9][10][11][12][13] would immediately benefit therefrom. In the case of the latter, for instance, the dosimetry protocols applied rely on a stable spectrally shaped proton distribution, currently guaranteed through passive filtering at the cost of experimental flexibility and achievable dose rate [8,14,15].…”