Nanodosimetry in a clinical neutron therapy beam using the variance-covariance method and Monte Carlo simulations

Abstract

Nanodosimetric single-event distributions or their mean values may contribute to a better understanding of how radiation induced biological damages are produced. They may also provide means for radiation quality characterization in therapy beams. Experimental nanodosimetry is however technically challenging and Monte Carlo simulations are valuable as a complementary tool for such investigations. The dose-mean lineal energy was determined in a therapeutic p(65)+Be neutron beam and in a (60)Co gamma beam using low-pressure gas detectors and the variance-covariance method. The neutron beam was simulated using the condensed history Monte Carlo codes MCNPX and SHIELD-HIT. The dose-mean lineal energy was calculated using the simulated dose and fluence spectra together with published data from track-structure simulations. A comparison between simulated and measured results revealed some systematic differences and different dependencies on the simulated object size. The results show that both experimental and theoretical approaches are needed for an accurate dosimetry in the nanometer region. In line with previously reported results, the dose-mean lineal energy determined at 10 nm was shown to be related to clinical RBE values in the neutron beam and in a simulated 175 MeV proton beam as well.

Nanodosimetry in a 12C ion beam using Monte Carlo simulations

“…6 that an agreement between the y D -ratios and a-ratios is found for a simulated object diameter of about 10 nm. This is consistent with previous findings for an X-ray beam, a neutron therapy beam and a proton therapy beam, and supports the previous suggestions that this size could be of relevance for radiation quality determinations in radiation therapy (Lillhök et al, 2007;Lindborg and Grindborg, 1997).…”

“…At this position, which is close to the maximum of the Bragg peak, the particles have relatively low energies and more amorphous track-structures with a resulting increase in y D with increasing object size (Lillhök et al, 2007).…”

“…For instance, a nanodosimetry-based linear-quadratic model of cell survival has been proposed by Wang et al (2007). In other studies, the ratio of the dose-mean lineal energies, y D , between a beam of interest and a reference 60 Co g beam, was correlated to the corresponding aratios from the linear-quadratic model (LQ-model) used in fractionated radiotherapy (Lillhök et al, 2007;Lindborg and Grindborg, 1997). A good correlation between the y D -ratios and a-ratios was found at an object size of 6e30 nm in an X-ray beam (100 kVp), at 10 nm in a p(65)þBe neutron therapy beam, and at 10 nm in a 175 MeV proton beam.…”

A Monte Carlo evaluation of carbon and lithium ions dose distributions in water

“…The microdosimetric parameters dose mean lineal energy y -D , frequency mean lineal energy y -F , dose mean specific energy z -D , and frequency mean specific energy z -F were calculated with the track-structure code PITS99, for the primary ion simulation, coupled with the KURBUC code for the delta electrons simulation. The details of microdosimetric calculations have been published elsewhere (Lillhok et al 2007.…”

Nanodosimetry – on the ''tracks'' of biological radiation effectiveness

“…Furthermore, theoretical investigations suggest that biological radiation effects originate in the interaction of different DNA lesions [26].In consequence, respective new developments have been started in the field of experimental nanodosimetry that aim at measuring the correlations of cluster-size distributions induced within a particle track in two separate nanometric targets in proximity [27], [28] or at obtaining a 3D image of the nanometric particle track structure for track segments of few 100 nm in length [29], [30], [31]. The latter would to some extent bridge towards microdosimetric measurements at the few-hundred nanometer regime [12]. A recent simulation study by Selva et al investigated the exploitation of the universal nanodosimetric relation [18] in radiotherapy by using (still only hypothetical) solid-state nanodosimeters that contain multiple targets of nanometric site size [32].…”