Nanodosimeter based on single ion detection

A nanodosimeter device for detecting positive ions induced in a sensitive gas volume by a radiation field of primary particles, comprising:

• an ionization chamber for holding the sensitive gas volume to be irradiated by the radiation field of primary particles, the ionization chamber having an aperture opening, wherein an electric field exists within the ionization chamber sufficient to cause the positive ions in the sensitive gas volume to drift toward the aperture opening;
• means for detecting the positive ions which pass through the aperture opening;
• means for determining an arrival time for the positive ions which pass through the aperture opening;
• means for position-sensitive detection of the primary particles passing through the sensitive gas volume;
• and
• means for correlating the arrival time of the positive ions relative to the position-sensitive data of primary particles.

A method for measuring positive ions induced in a DNA-size volume by a radiation field of primary particles, comprising the steps of

• providing a tissue-equivalent gas;
• determining a tissue-equivalent sensitive gas volume of the tissue-equivalent gas;
• providing a nanodosimeter comprising
• an ionization chamber for holding the tissue-equivalent sensitive gas volume to be irradiated by the radiation field of primary particles, the ionization chamber having an aperture opening, wherein an electric field exists within the ionization chamber sufficient to cause the positive ions in the tissue-equivalent sensitive gas volume to drift toward the aperture opening;
• an ion counter system connected to the ionization chamber, the ion counter system having an ion counter axially coincident with the aperture opening, for detecting the positive ions which pass through the aperture opening and arrive at the ion counter at an arrival time;
• a particle tracking system having a position-sensitive detector connected to the ionization chamber, for position-sensitive detection of the primary particles passing through the tissue-equivalent sensitive gas volume;
• and
• a data acquisition system having one or more interface boards, for receiving data from the ion counter system and the particle tracking system, capable of coordinating the readout of all data signals and of performing data analysis correlating the arrival time of the positive ions detected by the ion counter system relative to the position-sensitive data of primary particles detected by the particle tracking system;
• and
• scaling the data for the tissue-equivalent gas volume to a DNA-size volume.

A method for measuring positive ions induced in a DNA-size volume by a radiation field of primary particles, comprising the steps of

• providing a tissue-equivalent gas;
• determining a tissue-equivalent sensitive gas volume of the tissue-equivalent gas;
• providing a nanodosimeter comprising
• an ionization chamber for holding the sensitive gas volume to be irradiated by the radiation field of primary particles, the ionization chamber having an aperture opening, wherein an electric field exists within the ionization chamber sufficient to cause the positive ions in the sensitive gas volume to drift toward the aperture opening;
• means for detecting the positive ions which pass through the aperture opening;
• means for determining an arrival time for the positive ions which pass through the aperture opening;
• means for position-sensitive detection of the primary particles passing through the sensitive gas volume;
• and
• means for correlating the arrival time of the positive ions relative to the position-sensitive data of primary particles;
• and
• scaling the data for the tissue-equivalent gas volume to a DNA-size volume.

A method for measuring the differential value, w(E), of the mean energy necessary to produce an ion pair relative to a known value w(Eref) at a reference energy Eref comprising the steps of:

• providing a nanodosimeter comprising
• an ionization chamber for holding the sensitive gas volume to be irradiated by the radiation field of primary particles, the ionization chamber having an aperture opening, wherein an electric field exists within the ionization chamber sufficient to cause the positive ions in the sensitive gas volume to drift toward the aperture opening;
• an ion counter system connected to the ionization chamber, the ion counter system having an ion counter axially coincident with the aperture opening, for detecting the positive ions which pass through the aperture opening and arrive at the ion counter at an arrival time;
• a particle tracking system having
• a position-sensitive detector connected to the ionization chamber, for position-sensitive detection of the primary particles passing through the sensitive gas volume;
• and
• an energy measurement system for measuring the energy of the primary particles passing through the sensitive gas volume;
• selecting primary particles using the particle tracking system with reference energy Eref and a given energy E that pass the sensitive gas volume at a given distance y from the aperture opening;
• calculating the ratio of N1(Eref) and N1(E), being the average number of nanodosimetric ion counts for primary particle energies Eref and E;
• using the ratio of N1(Eref) and N1(E) as an approximation for the ratio of dN(Eref) and dN(E);
• and
• computing the differential value, w(E) according to the formula
• w(E)/w(Eref)=S(E)/S(Eref)/N1(Eref)/N1(E).

A method of calibrating radiation exposure from a radiation field with the presence or extent of damage to a nucleic acid within a sample, the method comprising the steps of:

• a) providing a nanodosimeter comprising an ionization chamber that comprises a tissue-equivalent gas;
• b) furnishing the sample;
• c) determining a tissue-equivalent sensitive volume of the tissue-equivalent gas;
• d) irradiating the tissue-equivalent gas and the sample with the radiation field;
• e) determining the number of positive ions induced within the tissue-equivalent sensitive volume by the radiation field;
• f) detecting the presence or extent of damage to the nucleic acid within the sample following irradiation with the radiation field;
• and
• g) comparing the presence or extent of damage to the nucleic acid with the sample in step (f) with the number of positive ions determined in step (e);
• were the presence or extent of damage to the nucleic acid within the sample is correlated with a radiation quality that is measured by determining an ionization spectrum.