JINST Instrumentation Theses Archive

Ms.C. degree thesis
accepted by Weizmann Institute, Israel, in 2003

Gili Assaf

Supervisor: Amos Breskin

Comparison of the biophysical effects on DNA, of protons and alpha-particles of equal mean

 Keywords:

• Dosimetry concepts and apparatus
• Microdosimetry and nanodosimetry
• Models and simulations
• Interaction of radiation with matter

 Abstract:
The objective of this project is the study of the physical and biological effects related to the stochastic nature of radiation-induced energy deposition in matter, in nanometric scales.

  The characterization of the biological effectiveness of ionizing radiation is currently evaluated by its LET value, corresponding to the mean ionization per unit length deposited at the cells' scales. However, it is now well recognized that the damage caused to the DNA molecule by stochastic radiation effects will determine the cell's chances of survival.

  In this work we prove, for the first time, that equal-LET particles differ in their biological effectiveness. The reason for this difference lies in the nanometric structure of the particles' ionization patterns, of which the spatial density depends on the particle type and energy.

  We base our research on the physical measurements of ionization patterns on nanometric, DNA-like, scales; we use a novel nanodosimetric experimental system developed in our group, measuring precisely the ionization in a small gas model of the DNA. In addition, we conduct direct biological measurements of the radiation-induced damage to plasmid DNA, in which we compare the type and amount of damage caused by the equal-LET particles. The experimental work is accompanied by extensive model-based simulations.

  We may conclude that the degree of ionization clustering on DNA scales is the most relevant in the determination of the biological effectiveness of ionizing radiation.