Analyzer for radiotherapy radiation beam
AssigneeRadiation Measurements, Inc.
InventorMelvin P. Siedband
Life of this patent
Estimating the term…
Abstract
A radiation detector has a number of ionization chambers. Each ionization chamber is connected to an accumulating capacitor which in turn is sequentially read by a multiplexed charge-counter. The charge-counter eliminates the effect of variations of the capacitance values of the accumulating capacitors associated with each ionization chamber cell and provides a consistency of measurement among the ionization chamber cells unlike a design employing multiple measurement circuits dedicated to each ionization chamber cell.
Claims9
A radiation detector having a plurality of radiation sensitive cells for characterizing a radiation beam over an area, comprising:
- charge generation means associated with each cell for generating an electrical charge related to the radiation received by the cell;
- accumulating capacitor connected to each charge generation means for accumulating the generated electrical charge;
- a charge-counter for receiving a charge and producing a magnitude signal indicating the amount of that charge, the charge counter including:
- a voltage detector for detecting the presence of at least a predetermined amount of charge on an accumulating capacitor to produce a charge present signal;
- a measuring capacitor for being connected to and disconnected from the accumulating capacitor;
- an oscillator receiving the charge present signal and for repeatedly connecting and disconnecting the measuring capacitor to and from the connected accumulating capacitor, during a cycle, so that charge may move between the connected accumulating capacitor and the measuring capacitor when they are connected only so long as the charge present signal is present;
- a bias means for restoring a substantially constant voltage difference between the accumulating capacitor and the measuring capacitor when the measuring capacitor is disconnected to provide a substantially constant amount of charge flow between the accumulating capacitor and the measuring capacitor each time they are connected;
- and
- counter means connected to the oscillator and the voltage detector for counting the total number of connections and disconnections of the measuring capacitor during the charge present signal;
- a multiplexer for connecting each accumulating capacitor in sequence to the charge-counter for sequentially measuring the charge accumulated on the accumulating capacitor to produce a magnitude signal associated with each accumulating capacitor.
In a radiation detector having a charge generating means for generating a charge related to the received radiation and an accumulating capacitor for collecting said charge, a charge-counter for measuring the accumulated charge and hence the received radiation, the charge-counter comprising:
- a voltage detector for detecting the presence of at least a predetermined amount of charge on the accumulating capacitor to produce a charge present signal;
- a measuring capacitor for being connected to and disconnected from the accumulating capacitor;
- an oscillator receiving the charge present signal and for repeatedly connecting and disconnecting the measuring capacitor to and from the accumulating capacitor, during a cycle, so that charge may move between the accumulating capacitor and the measuring capacitor when they are connected only so long as the charge present signal is present;
- a bias means for restoring a substantially constant voltage difference between the accumulating capacitor and the measuring capacitor when the latter is disconnected to provide a substantially constant amount of charge flow between the accumulating capacitor and the measuring capacitor when they are connected;
- and
- counter means connected to the oscillator and the voltage ionization chamber for counting the total number of cycles of connections and disconnections of the measuring capacitor during the gating signal.
A radiation detection system comprising:
- at least one radiation detector having a plurality of radiation sensitive cells for characterizing a radiation beam over an area, including:
- charge generation means associated with each cell for generating an electrical charge related to the radiation receiving by the cell and subject to a sensitivity variation;
- accumulating capacitor connected to each charge generation means for accumulating the generated electrical charge;
- a charge-counter for receiving a charge and producing a magnitude signal indicating the amount of that charge;
- and
- multiplexer for connecting each accumulating capacitor in sequence to the charge-counter for sequentially measuring the charge accumulating on the accumulating capacitor to produce a magnitude signal associated with each accumulating capacitor;
- a controller connected to the charge counter of the radiation detector to receive the magnitude signal and for controlling the multiplexer for selectively reading the magnitude signal associated with a given cell for the selected one radiation detector;
- and
- the controller including a weight table having a weighting value associated with the given cell and a means for applying the weighting value to the magnitude signal to correct for the sensitivity variation associated with the cell.
Dependencies are inferred from the claim text.