Role of shielding in modulating the effects of solar particle events: Monte Carlo calculation of absorbed dose and DNA complex lesions in different organs F. Ballarini a,b, * , M. Biaggi c , L. De Biaggi c , A. Ferrari b,d , A. Ottolenghi a,b , A. Panzarasa b , H.G. Paretzke e , M. Pelliccioni b , P. Sala b,f , D. Scannicchio a,b , M. Zankl e a Dipartimento di Fisica Nucleare e Teorica, Universit a degli Studi di Pavia, via Bassi 6, I-27100 Pavia, Italy b INFN, National Institute of Nuclear Physics, Italy c Universit a degli Studi di Milano, Dipartimento di Fisica, via Celoria 16, I-20133 Milano, Italy d CERN, European Laboratory of Particle Physics, CH-1211, Geneva 23, Switzerland e GSF-National Research Centre for Environment and Health, Institute of Radiation Protection, 85764 Neuherberg, Germany f ETH Zurich, CH-8093 Zurich, Switzerland Received 19 October 2002; received in revised form 13 August 2003; accepted 15 August 2003 Abstract Distributions of absorbed dose and DNA clustered damage yields in various organs and tissues following the October 1989 solar particle event (SPE) were calculated by coupling the FLUKA Monte Carlo transport code with two anthropomorphic phantoms (a mathematical model and a voxel model), with the main aim of quantifying the role of the shielding features in modulating organ doses. The phantoms, which were assumed to be in deep space, were inserted into a shielding box of variable thickness and material and were irradiated with the proton spectra of the October 1989 event. Average numbers of DNA lesions per cell in different organs were calculated by adopting a technique already tested in previous works, consisting of integrating into ‘‘condensed-history’’ Monte Carlo transport codes – such as FLUKA – yields of radiobiological damage, either calculated with ‘‘event-by-event’’ track structure simulations, or taken from experimental works available in the literature. More specifically, the yields of ‘‘Complex Lesions’’ (or ‘‘CL’’, defined and calculated as a clustered DNA damage in a previous work) per unit dose and DNA mass (CL Gy 1 Da 1 ) due to the various beam components, including those derived from nuclear interactions with the shielding and the human body, were integrated in FLUKA. This provided spatial distributions of CL/cell yields in different organs, as well as distributions of absorbed doses. The contributions of primary protons and secondary hadrons were calculated separately, and the simulations were repeated for values of Al shielding thickness ranging between 1 and 20 g/cm 2 . Slight differences were found between the two phantom types. Skin and eye lenses were found to receive larger doses with respect to internal organs; however, shielding was more effective for skin and lenses. Secondary particles arising from nuclear interactions were found to have a minor role, although their relative contri- bution was found to be larger for the Complex Lesions than for the absorbed dose, due to their higher LET and thus higher biological effectiveness. Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Shielding effects; Solar particle events; Calculation of absorbed dose; DNA complex lesions 1. Introduction and rationale The interest in manned space exploration missions is increasing more and more. NASA’s plans include a human mission to Mars in the first half of the 21st century (Cucinotta et al., 2001); a possible launch by 2018 would allow for energetically favorable flight * Corresponding author. Tel. +39-02-5031-7399; fax: +39-02-5031- 7630. E-mail address: francesca.ballarini@mi.infn.it (F. Ballarini). 0273-1177/$30 Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2003.08.055 Advances in Space Research 34 (2004) 1338–1346 www.elsevier.com/locate/asr