High LET Effects

Gervais B, Beuve M, Olivera GH, Galassi ME (2006) Numerical simulation of multiple ionization and high LET effects in liquid water radiolysis, Radiation Physics and Chemistry 75 493-513... 

A summary of the clinical results obtained with neon ions in Berkeley is presented in Table 7 [4,47]. Some fast neutron therapy results are also presented. Although the recruitments are not comparable, it should be pointed out that tumor types or sites for which an advantage was found with neon ions are those for which an advantage was also found with fast neutrons. This suggests a specific high-LET effect. 

Pradhan and Bhatt (1982) used TLD discs of CaS04 Dy with 75% teflon. Grain sizes were below 74 [xm and disc thicknesses 0.2 and 0.8 mm. Phosphors were sensitized by prolonged y pre-irradiation followed by 1 hour annealing at 350 C. The treatment has increased the TL response by a factor of 2.3 at 1.25 MeV and came down to 1.4 for 8 keV X rays. The reduction in the TL enhancement at low photon eneigies was attributed to the high LET effects at these photon energies. 

Goldman, M., An overview of high LET radiation effects in cells, in The Health Effects of Plutonium and Radium (W. S. S. Jee, ed.), pp. 751-766, J. W. Press, Salt Lake City, Utah (1976). 

Charge exchange is important all along the high-LET tracks. The effective ionic charge is determined by cross sections of electron capture and loss, which depend predominantly on the ionic velocity. Electron loss may be simply described by an ionization of the incident ion in its own reference frame due to the impact of medium electrons and nuclei. Following Bohr (1948), Mozumder et al. (1968) wrote the cross section for this process as1... 

First, we want to make a comment about possible local temperature rise due to energy absorption. An early theory of radiation effect s was based on the point-heat hypothesis (Dessauer, 1923). Later analysis showed that the temperature rise would be too feeble and too transient for low-LET radiation to cause any real change (see Mozumder, 1969). There is no experimental evidence for temperature rise for low-LET radiations. The case of high-LET radiations is still open, though. 

For a given medium such as water, its density and the velocity of the incident heavy ion contribute to the formation of the columnar track structure. The spacing of the primary energy loss events must be within the delocalization of the secondary electrons for elfects attributed to high LET to occur. For this reason, typical LET effects will not be... 

Improving the radiobiological differential effect between the cancer and normal cell populations. This second approach is more complex and involves radiobiological considerations. New and different radiation qualities have been considered such as high-LET radiations. Some of the radiobiological issues involved in the use of high-LET radiation, in particular the RBE concept, are discussed in Sec. 3. 

Improving the radiobiological differential effect fast neutrons and other high-LET radiations... 

Among high-LET radiations, fast neutrons were first introduced to exploit a radiobiological differential effect no benefit is expected from the physical selectivity. 

High-LET Advantage. Thirdly, high-LET irradiation is delivered at the level of the SOBP where the PTV (thus the cancer cell population) is located. Heavy-ion beams are thus specifically effective against some tumor types as discussed for fast neutrons (see Secs. 4.1.1 and 4.1.3). 

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