EP2211595A1

EP2211595A1 - Coaxial-cable linac for iort and industrial radiography

Info

Publication number: EP2211595A1
Application number: EP09425017A
Authority: EP
Inventors: Pompilio Gatto
Original assignee: Italian Linear Accelerator High Technology System Srl
Current assignee: Italian Linear Accelerator High Technology System Srl
Priority date: 2009-01-23
Filing date: 2009-01-23
Publication date: 2010-07-28

Abstract

Linear electron accelerator including an oscillator (5) and a radiating head containing a linear electron accelerating cavity (1), emitting an electron beam at an output thereof (3), and fed by the oscillator through a coaxial cable (7).

Description

Technical Field

The present invention relates to the field of linear electron accelerators (or 'linacs') for intraoperative radiation therapy and industrial radiography.

Background of the Invention

A linear electron accelerator includes a linear electron accelerating cavity, assembled in a radiating head, which accelerating cavity generates an electron beam which is emitted to the outside through an output port. The accelerating cavity is fed by a radioelectric radiofrequency (RF) signal at the output of a modulator assembly including an oscillator, e.g. a magnetron (for low powers) or a klystron (for high powers) which generates the electromagnetic waves of the RF signal.
In the linacs for IORT the radiating head is assembled in a linkage movably in roll and pitch to an extremity of a support arm. The modulator assembly is assembled to an opposite extremity of the support arm.
The RF signal is carried from the oscillator to the accelerating cavity through a waveguide in prior art.
However, a problem is associated of the stability of the frequency and of the power of the RF signal in carrying it from the oscillator to the accelerating cavity.
Moreover, waveguides are not protected against vibrations, shocks and external temperature; being in not an elastic, but iron rigid material, they are affected by problems of possible vibratory mechanical and thermal shifts, particularly in correspondence with joints.
Moreover, in the search for the best means for making the radiating head as mobile as possible, and therefore free from the body of the accelerator, which the radiating head is assembled upon, to give the maximum freedom of the positioning of the output port of the radiating head, to achieve the due docking of it in IORT with a surgical breech which to carry out a radiation therapy onto, one had passed to utilize an external flexible waveguide in

prior art.

However, this one gives problems of physical rupture in the phases in which the pitch rotation and the roll rotation of the radiating head compose with each other, owing to the twisting which the flexible waveguide is subjected to in such phases, and therefore strongly limits the mechanics of the rotation of the radiating head.
Therefore, one has passed to utilize a rotary joint able to carry the RF signal coming from the oscillator. This rotary joint enables the rolling rotation of the radiating head up to the full round angle (360°), therefore with full mechanical freedom; but the art still remains tied to the use of an internal waveguide for the pitch motion.
In a subsequent solution one has passed to utilize not one, but two rotary joints capable of carrying the signal generated by the oscillator. A first joint thereof enables the rolling of the radiating head up to 360°, whilst a second joint enables the pitching of the head up to the straight angle (180°). These two motions, composed together, give a freedom of the positioning of the output port of the radiating head in any position, as is necessary to achieve a perfect docking of it with a surgical breech.
However, the latter solution too has the drawback of bringing a heaviness of the accelerator and a considerable increase of the costs of the manufacturing thereof.
Therefore, it is the object of the present invention to provide a linear electron accelerator that solves the problems connected with the waveguides related to keeping the frequency and the power of the signal generated by the oscillator in carrying it to the accelerating cavity, and the fragility of waveguides to external stresses.
It is also the subject of the present invention to reduce the weight of the accelerator.
Such objects are reached by substituting waveguides with coaxial cables.
Tests have been carried out with coaxial cables, aimed at the object of carrying the RF signal, under the aspects of both frequency and power stability in the transfer thereof from the oscillator to the accelerating cavity.
It has been surprisingly observed a great stability of the signal in any ambient condition. As opposite to with waveguides, the ambient temperature does not minimally modify the frequency stability of the signal, and temperature is a very important parameter, particularly if the accelerator is used in not air-conditioned rooms or for a long time by endogenous heating.
Moreover, it has been surprisingly found that coaxial cables are able to transmit very-high frequency signals, i.e. more than 32 GHz, without either frequency or power signal degradation.
Coaxial cables, as opposite to waveguides, are protected and therefore inherently resistant to external stresses.
Particularly, the present invention envisages the substitution of the aforesaid rotary joints of prior art with miniaturized rotary joints for coaxial cables.
An inventive accelerator includes components that afford superior performances and are lighter and cheaper at a time.
The present invention solves the problem of carrying the frequency generated by the oscillator to the accelerating cavity through components 'dematerialized' relative to those used in prior art, which bring advantages exceptionally considerable as regards weight and cost. A substantial weight lowering is determined between a prior art accelerator and an inventive one consequently to the substitution of the rotary joints with coaxial cables jointed with miniaturized rotary joints for coaxial cables.
The present invention brings an advantage also for the quickness of the assembly of the machine and also for the compactness of the overall dimensions of the machine.
The present invention is also concerned with industrial radiography applications of linear accelerators. The radiography can be carried out in the bunker or in the field.
In the first instance it is supposed that the piece to be radiographed is brought in a bunker and there positioned according to procedures that describe the best situations in order to achieve an optimum radiograph. The procedures dictate the position and the distance of the piece relative to the radiating head of the linear accelerator.
In the second instance it is the linear accelerator which is brought in the field to radiograph a piece which may be a component inserted in a system which it cannot be detached from. E.g. a pipe welded in a pipeline may be dealt with to the object of testing the perfect tightness of the welds.
It is necessary in the radiography in the field that the radiating head may be positioned in correspondence of a site to be radiographed.
As this is difficult or impossible to be realized with present accelerators, the present invention has the further object of providing a linear electron accelerator wherein the radiating head can be easily and precisely positioned in correspondence with a site to be radiographed.
Such an object is reached by mechanically freeing the radiating head from the machine body of the accelerator. The freed head is electrically connected with the power supply through the aforesaid coaxial cable as a flexible electric connection. The coaxial cable is extended coming out of the machine body. Experimental tests have proved that there is not a degradation of the RF signal emitted by the radiofrequency oscillatore for a coaxial cable length in a field between 3 and 4 meters. Complementary means are provided on the machine body and on the radiating head for removably assembling the radiating head to the machine body in a rest position.

Subject of the Invention

Therefore, it is the subject of the present invention a linear electron accelerator according to enclosed Claim 1.
Preferred embodiments are set forth in the subclaims.

Brief Description of the Figure in the Drawings

The present invention will be fully understood based on thye following detailed disclosure of embodiments thereof, only given as a matter of example, absolutely not of restriction, referring to the annexed drawings, wherein:

FIGURE 1 is a perspective view of an electron accelerator according to the present invention with removed portions with the functional constitutive elements at sight;
FIGURE 2 illustrates a linear electron accelerator according to the present invention having a separable head for industrial radiography in the field in a rest position, and
FIGURE 3 depicts the same with the head extracted, in a working position.

Best Way for Carrying Out the Invention

Referring to FIGURE 1, a linear electron accelerator includes a linear electron accelerating cavity 1 having an electron beam output port 3, and a modulator assembly 5, including power transformers, power supplies, an oscillator, e.g. a magnetron or a klystron, and stabilizers. The oscillator generates electromagnetic waves forming a RF radioelectric signal which feeds accelerating cavity 1. Accelerating cavity 1 and modulator assembly 5 are arranged at opposite extremities of a support arm, whereto means are assembled for carrying the signal generated by the oscillator to the accelerating cavity. These means according to the inventive concept include: a coaxial cable 7, preceptive, interfaced with modulator assembly 5 through an adapter 11 between coaxial cable 7 and an output waveguide stub of the oscillator. Coaxial cable 7 is supported along its path by a suitably shaped mechanical support piece 9. Coaxial cable 7 is interfaced at its other extremity with accelerating cavity 1 through an adapter 13 between coaxial cable 7 and an input waveguide stub of the accelerating cavity.
Coaxial cable 7 has a 'U' bend 7' along its path. The coaxial cable, upstream of 'U' bend 7', downstream of modulator assembly 5, has an interruption of its mechanical continuity restored rotatingly by means of a first miniaturized rotary joint for coaxial cables 15. Coaxial cable 7 on the arm of the 'U' bend immediately upstream of accelerating cavity 1, has an interruption of its mechanical continuity restored rotatingly by means of a second miniaturized rotary joint for coaxial cables 17.
First and second miniaturized rotary joint for coaxial cables 15, 17 have their respective rotation axes along different directions, preferably perpendicular to each other.
First joint 15 is for enabling a rolling motion of the radiating head; second joint 17 is for enabling the pitching motion of the radiating head.
Referring to FIGURE 2 and to FIGURE 3, the linear electron accelerator may have radiating head 101 not integral with the machine body of the accelerator, but forming a separate piece. The machine body of the linear accelerator is endowed with vertical guides 103 with a bottom abutment for hooking radiating head 101 thereto by means 103' complementary to vertical guides 103 when it does not work. The coaxial cable that electrically connects the radiating head to the oscillator generating electromagnetic waves includes an extension 105 that comes out of the machine body of the accelerator. The radiating head, once freed from guides 103, can be approached to a site of interest, particularly a site which is hard to reach, by exploiting the flexibility and the length of coaxial cable extension 105.
The present invention has been disclosed and depicted referring to specific embodiments thereof, but it is to be expressly understood that variations, additions and/or omissions may be brought thereto without departing from the scope of protection thereof, which only remains restricted by the enclosed claims.

Claims

Linear electron accelerator including a machine body and means for generating electromagnetic waves (5), and a radiating head including means forming a linear electron accelerating cavity (1), emitting an electron beam at an output thereof (3), and which are supplied by said means for generating electromagnetic waves through guiding means, characterized in that said guiding means are coaxial cable means (7).
Linear electron accelerator according to Claim 1, wherein said radiating head is assembled to said machine body by means of a linkage that supports it movably for rolling and pitching, and said coaxial cable means are broken into tracts successively connected by means of miniaturized rotary joints for coaxial cables (15, 17) which have their respective rotation axes along two different directions, to enable rolling and pitching motions of said radiating head.
Linear electron accelerator according to Claim 1, wherein said radiating head (101) is a piece separated from said machine body, and said coaxial cable means that electrically connect the radiating head to said means for generating electromagnetic waves include an extension (105) coming out of the machine body.