JPS5823704B2 - Equipment for monitoring the position, intensity, uniformity and directivity of ionizing radiation beams - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an improvement in a device for monitoring the position, intensity, uniformity and directivity of an ionizing radiation beam of the type described in the specification of the original patent application (Patent No. 983,925). and more particularly to an ion collection electrode located within the ionization chamber of the device.

According to this invention, the position, intensity,
The uniformity and directional monitoring devices are respectively first . Second
having at least a first degree second ionization chamber with a circular electrode;
The area S2 of the second circular electrode is smaller than the area S1 of the first circular electrode, the area S1 is approximately equal to the cross-sectional area of the ionizing radiation beam, and the area S2 of the first circular electrode is smaller than the area S1 of the first circular electrode. The second circular electrode is combined with a circuit for processing the electrical signals collected and further has a safety device for controlling a radiation source controlled by said circuit and generating a beam of ionizing radiation.

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the invention and to show how it may be practiced, reference is made to the accompanying drawings.

FIG. 1 shows a first embodiment of two ionization chambers used in a monitoring device according to the invention.

These ionization chambers 1, 2 each consist of two circular electrodes E, each constituted by a frame C supporting a sheet of polyethylene terephthalate, known by the trade name "MYLAR", as shown schematically in FIG. 2, for example.

12EO2, on which a thin metal film transparent to the ionizing beam is deposited by vacuum deposition.

Electrode E.

The diameter d1 of 1 is approximately equal to the diameter of the ionizing beam, and the diameter d1 of the electrode E.

The diameter d2 of 2 is the electrode E. 1 diameter d1.

Area S of each electrode. 1 t 802 is 801>802 There is a relationship between

In operation, electrode E.

Ionization flux φ1 that intersects 1 t EO2
．． φ2 is electrode E.

1 t The current collected by EO2 ■.

1 t Proportional to IO2. Assuming that the flux is uniform, electrodes placed in these electrode chambers with upper and lower metalized transparent walls (not shown) will have a negative polarity with respect to these walls. It should be noted that the biases are suitably biased by nearly identical biases.

In FIG. 3, graph a represents electrode E for a uniform, properly centered radiation beam.

The current along the diameter axis XX of 1■.

1 and thus the variation of the flux φo1, and graph b shows the above electrode E when the radiation beam is not uniform (in the considered example the ionizing beam is denser in the center than in the periphery).

The current collected by 1■. It shows a variation of 1.

Therefore, the current ■. 1 t IO2 is no longer electrode EOI t
It is proportional to the area of EO2 sot t 802, and the formula (
2) Two comparators CPo1. Electrode E by means of a circuit consisting of CPo2 (FIG. 4).

1 j Current collected by EO2■.

1 j Voltage corresponding to IO2■. 1 j VO2, so the safety device SS is triggered when .

■The threshold value is a threshold voltage of a given value and is related to the operating parameters or characteristics of the irradiation device.

The ionization chambers 1, 2, in which the intensity, uniformity and directivity of the radiation beam can be controlled, can be replaced by a separate ionization chamber (Fig. (not shown).

In a second embodiment, the device according to the invention has two ionization chambers, each equipped with two circularly segmented electrodes E, , E2, shown schematically in FIG.

Two insulating strips 3, 4 ('MYL without metallization)
AR'') consists of electrode E1 and two elements e11 t
In e12, electrode E2 is also connected to two other elements e2□, e22
These insulating strips 3, 4 are 90 mm apart from each other.
arranged at an angle of .

The area S1 of the electrode E1 is approximately equal to the cross-sectional area of the ionizing beam, and the area S2 of the electrode E2 is smaller than the area S1 of the electrode E1.

In operation, electrode E1. Element e12°12 of electrode E2
Pass through tti22.

Electrode E1. 3 ionizing radiation fluxes φ1. φ2 are the electrodes E1. Current 1 flowing through E2
1=i11+i12. It is proportional to l2=i21+i22.

Assuming that the flux is uniform, the following relational expression holds.

In operation, dl, d2 are connected to electrodes E1. E2, the eccentricity △d according to the axis of the insulating strip 3 of the electrode E0 such that
Considering the most unfavorable case of a non-uniform radiation beam with a collected current of 11. (2) The following relationship is obtained by comparing 2.

Inequalities (6) and (8) will therefore activate an alarm or safety device to stop the radiation beam.

In the case of a uniform beam that is eccentric, the following relationship is obtained:

Inequality 11) causes the emission of the radiation beam to be stopped by a safety device.

However, it should be pointed out that a centered uniform beam forms the same relationship as 9), (10), (11) to the output of the monitoring circuit.

As in the previous case, inequality (11) results in the activation of the safety device and thus stopping the emission of the radiation beam.

In the embodiment described here, therefore, the reliability of the operation of the device is guaranteed, but no indication of defects appearing in the radiation beam is provided.

In two other preferred embodiments (Figures 6 and 7):
Defects appearing in the beam are displayed.

FIG. 6 shows two electrodes E3 used in the device according to the invention.
．． E4 is schematically shown.

Electrode E3 has 40 elements e31 t e32 j e33
The electrode E4 consists of a single element e4.

In operation, the current ■3=i3□+t32+t330i
By measuring 3+, it is possible to monitor the flux φ, i.e. the radiation dose which is proportional to the current I3, which flux φ is also monitored in the second ionization chamber supplying the current.

If Zara-t, then the centering of the beam is obtained, If , beam uniformity is satisfied.

In the above-mentioned method, k is 1 considering the imposed safety standards.
The coefficient is close to .

If the radiation beam is a scanning beam, the monitoring of the centering of the beam can be carried out, for example, by four elements e3.

This can be achieved by combining an ionization chamber equipped with an electrode E3 equipped with an e33t e34 with a centering device of the type described in JP-A-51-16981; Two electrodes such as El j E2 with two elements each can be combined.

In another embodiment, a monitoring device according to the invention is provided with electrodes E5, E6, . It is equipped with three ionization chambers 5, 6, 7 equipped with E7 °C.

Electrode E3. E6 has substantially the same diameter as the radiation beam, and each electrode has two elements e5, respectively.

It consists of e5□, eQ□, and e62.

The relatively small diameter electrode E7 consists of only one element e7.

Element e51 j e52 of electrode E5 is element e6 of electrode E6.

e62 and element e7 of electrode E7 each have a current i5□
.

Collect i52 j : i61 t 162 : i7.

In the case of a non-uniform beam (this non-uniformity is due, for example, to the absence of a correction filter or to some defect in the beam scanning action), the following relationship is obtained:

These inequalities trigger safety devices to interrupt operation of the radiation source or control the ionizing beam.

FIG. 8 shows electrode E5. E6. One implementation of a circuit for processing signals acquired at E7 is shown.

Amplifiers A, , A5□ generate a voltage proportional to the current "51 t i52.

Operational amplifier AS5 generates a voltage VS5 proportional to the sum of currents i5□+is2.

The variable resistor R5 allows the measurement value to be calculated so that the sum of the above currents represents the dose measured in the ionization chamber 5 on a given scale.

Operational amplifier AD5 has a current difference of 151! A voltage D5 proportional to 52 is generated.

Variable resistance R5□ is two elements of electrode E5 6517652
Any slight asymmetry that may exist between them can be guaranteed.

Similar elements are designated with corresponding symbols in the processing circuitry belonging to electrode E6.

Amplifier A. 7 generates a current 17 and thus a voltage 7 proportional to the dose collected at the electrode E7.

Voltage VS5. ■S6. ■7 are comparators C"1, (:p,, t C"3 +C"4, respectively, as shown in Fig. 9.
)CP, , CP6.

Resistors R1-R7 allow the value of the signal applied to the comparator to be adjusted to account for mechanical inaccuracies in manufacturing.

Since the area of electrode E, is larger than the area of voltage E7, voltage VS5 is the North Star, or electrode E7. Area of E5 S7゜S5
Voltage ■ is larger than S7 in the ratio of .

The resistors R1°R2 and R3 have resistance values such that the voltage V7 satisfies the following double inequality.

If this double inequality is not satisfied, the comparator .

CPl or CP2 (related to imbalance) is the safety device S
Generates a positive output voltage or signal K that triggers 5.

Comparator CP3. CP4 triggers the safety device SS when the dose exceeds a given value ■.

On the other hand, comparator CP5. CP6 is the voltage ■S5. ■ Between S6 and therefore electrode E5. Trigger the safety device if there is any discrepancy between the doses measured at E6.

In another embodiment shown in FIG. 10, electrode E5. E6
．． The current collected by element E7 is transferred to multiplier M and computer C.
A device constituted by an analog-to-digital converter CA in combination with L is supplied to a device which performs a check of the above-mentioned conditions and controls a safety device SS to shut down the radiation beam source if these conditions are not met.

Additional Relationship This invention is based on the original invention [Patent No. 983925 (Special Publication No. 54
-16872)], i.e., [having at least one ionization chamber equipped with an ion collecting electrode, said electrode comprising a number of electrically conductive and electrically insulated elements from each other, said elements comprising a beam of ionizing radiation. arranged in relation to each other so as to simultaneously measure the ion currents corresponding to the central and peripheral regions, said elements being coupled to a processing circuit for processing the collected electrical signals, and said processing circuit for monitoring said beam; In a monitoring device for controlling the centering, intensity, uniformity and directivity of a beam of ionizing radiation adapted to irradiate a target of predetermined dimensions, the monitoring device is coupled with a device, characterized in that each 1. A second circular electrode is provided such that the area S2 of the second electrode is smaller than the area S1 of the first circular electrode, the area S is approximately equal to the cross-sectional area of the ionizing radiation beam, and the area S2 of the second circular electrode is smaller than the area S1 of the first circular electrode. The invention is characterized in that it combines a circuit for processing an electrical signal that collects a second circular electrode, and is further provided with a safety device that is controlled by the circuit and controls a radiation source that generates an ionizing radiation beam. An invention is an addition to the original invention in that it achieves the same purpose as the original invention.

[Brief explanation of the drawing]

1 shows a monitoring device having two ionization chambers according to the invention, FIG. 2 schematically shows two electrodes of the type used in the two ionization chambers according to the invention, and FIG. 3 shows the electrodes according to the invention. FIG. 4 schematically shows a comparator circuit in combination with these electrodes, and FIG. 5.6.7 shows two examples of the distribution of the intensity of the radiation along the diametric axis of the 8.9, 1.
Figure 0 is a diagram of a processing circuit and two comparator circuits, respectively, making it possible to monitor the position, intensity, uniformity and directivity of the ionizing radiation beam. In the figure, 1 and 2 are ionization chambers, EOI j E02 circular electrode C
Po1. CPo2 is a comparator, El and R2 are circular split electrodes, 3 and 4 are insulating strips, ell t e12 s e21
t e2□ is an element, R3 and R4 are electrodes, e31. e3
2. e33゜e34 t e4 is element 1 R5, R6,
R7 is the electrode ne51゜e52, e61t e6
2 t e7 is an element, A51 t A52 is an amplifier, R
51t R5□ is a variable resistor, Ar1 is an operational amplifier, Ao
7 is an amplifier, CP1 to CP6 are comparators, R1 to R71d
The resistor, SS, is a safety device.

Claims (1)

[Scope of Claims] 1. At least two ionization chambers each having one electrode, the area of one electrode of the two ionization chambers being smaller than the area of the electrode of the other ionization chamber, the area of the electrode of the other ionization chamber is approximately equal to the cross-sectional area of the ionizing radiation beam; ionization, characterized in that it is combined with a processing circuit for processing the electrical signals supplied by these electrodes, said processing circuit controlling a safety device, and said safety device controlling a radiation source of said ionizing radiation beam. Equipment for monitoring the position, intensity, uniformity and directionality of sexual radiation beams. 2 Each electrode consists of two semicircular elements separated from each other by an electrically insulating diametric strip, the electrically insulating strip of one electrode being at right angles to the electrically insulating strip of the other electrode. A device for monitoring the position, intensity, uniformity and directivity of an ionizing radiation beam according to claim 1, characterized in that the device is located at: 3. The position of the ionizing radiation beam according to claim 1, characterized in that one electrode is divided into four approximately quarter-circular elements and the other electrode consists of a single element. , intensity, uniformity and directionality monitoring equipment. 4 having two ionization chambers, two of which are each equipped with an electrode approximately the same size as the cross-sectional area of the radiation beam, each electrode separated from the other by an electrically insulating diametric strip; the electrically insulating strips are arranged at right angles to each other, the remaining electrode chambers are provided with a single-element electrode; The device for monitoring the position, intensity, uniformity and directivity of an ionizing radiation beam according to claim 1, characterized in that the size of the electrodes in the two electrode chambers is smaller than the size of the electrodes in the two electrode chambers. 5. A comparator in which each electrode is associated with a processing circuit for processing the signals supplied by the elements of the electrode, making it possible to compare the sums and differences of the signals supplied by the elements for each electrode above a predetermined threshold. The position and intensity of the ionizing radiation beam according to claim 1, characterized in that it is equipped with a circuit and a safety device that allows the radiation source to be controlled when the measurement signal has a value different from the threshold value. , uniformity and directional monitoring devices. 6. A comparator, in which the electrodes of the two ionization chambers are associated with a respective processing device, enabling said processing device to compare the sums and differences of the signals supplied by the elements of said electrodes for each electrode with predetermined threshold values. The circuit includes another comparator that allows the signal supplied by the electrode of the remaining one ionization chamber to be compared simultaneously with the sum of the signals supplied by both ionization chamber elements, and the measured value is equal to the threshold value. The position, intensity, uniformity and directivity of the polarized radiation beam according to claim 4, characterized in that it is provided with a safety device that makes it possible to control the radiation source when having different values. monitoring equipment.