Chromosome Aberrations by Heavy Ions - Radiation Damage in Biomolecular Systems - page 373

between chromosome aberrations and cancer were also proposed (e.g. [ 9 ]). Further-
more, aberration yields are used for biodosimetry applications, and more generally
as biomarkers of exposure and risk [ 10 ]. In particular, the frequency of CAs in
peripheral blood lymphocytes (PBL) was used to evaluate radiation exposure in
victims of accidents including Chernobyl [ 11 - 19 ], in survivors of the Hiroshima
and Nagasaki A-bombs [ 20 , 21 ], and in astronauts exposed to the complex radiation
environments encountered in space [ 22 - 26 , 29 ].

22.1.2 Why should we care about heavy ions?

A possible scenario where human beings are exposed to heavy ions is tumour
treatment with Carbon ions, which are now used by an increasing number of
radiotherapy centres including Chiba (with about 3,000 patients treated until
now) and Hyogo, in Japan, and Darmstadt in Germany. Other Carbon facilities
started operating more recently in Pavia (Italy), Heidelberg (Germany) and other
locations (see [ 27 ] for a review). Like protons, Carbon ions are characterized by
a localization of energy deposition in the so-called “Bragg peak” region. This
provides an improved dose conformation, also considering that their Relative
Biological Effectiveness (RBE) in the plateau is sufficiently low (approximately 1,
like for protons). Furthermore, Carbon beams are particularly suitable for treating
radioresistant tumours because their RBE for clonogenic inactivation in the region
of the (spread-out) Bragg peak can be up to 3 (also depending on the beam features,
the considered cell line etc.), to be compared with the 1.1 value typically adopted for
proton beams. However, treatment planning with heavy ions is particularly complex,
also considering that at the energies of interest for hadrontherapy nuclear reactions
of the primary particles with the beam-line constituents and with the various
components of the human body play a non negligible role: projectile fragmentation
gives rise to lighter fast particles which form a “tail” of dose beyond the SOBP. It is
therefore of utmost importance to characterize hadrontherapy beams, and it is also
desirable to monitor to what extent normal tissues are spared during the treatment.
Blood is a normal tissue which is unavoidably exposed during radiotherapy, and the
yield of chromosome aberrations in peripheral blood lymphocytes is considered as
a reliable estimate of the equivalent whole-body dose [ 28 ]. Lymphocytes circulate
in the blood vessels and are distributed throughout the body, mainly in lymph
nodes, spleen, bone marrow, thymus and the gut lymphoid tissue. Damage to the
haematopoietic tissue is therefore a major limiting factor with respect to the total
dose delivered in a radiotherapy treatment, both for acute morbidity and for the
risk of developing secondary cancers [ 29 ]. In this framework, Durante et al. [ 14 ]
monitored the induction of chromosomal aberrations in PBL of cancer patients
treated with X rays or Carbon ions at NIRS in Chiba, finding that the lymphocytes
from C-ion patients carried less aberrations than those from X-ray patients. More
details are reported in section 22.2.2 .