High strength low attenuation couch top

Abstract

In the diagnosis of tumours and the like, particularly by means of X-ray radiographs and the gamma therapy of such afflicted patients' difficulties have been encountered with prior known stretchers due to the excessive attenuation of the X-rays and the gamma ray because no suitable structural material of low cost has been discovered. Beryllium sheet, wood and plastic sheet are all suitable, but beryllium is costly; wood and plastic structures of sufficient transparency tend to deflect excessively. These prior difficulties have been further magnified when the X-ray beam has been projected obliquely to the plane of the stretcher. The present invention provides a relatively low cost structure having a greatly enhanced strength to weight ratio and a lower transparency to X-rays. The latter feature resulting in lower radiation dose to the patient than previously possible.

Description

This invention relates to lightweight structures having low transparency to photons. The invention has particular, but not exclusive, utility when applied to diagnostic and therapy stretchers.

Prior known diagnostic stretchers have been made of a variety of materials, the most sophisticated of which have utilised a glass-fibre reinforced polyester shell around a polyurethane foam core. The attenuation of such stretches to X-rays of about 90 kvp has been found equivalent to about 3mm of aluminum. New regulations require diagnostic and therapy stretchers to have an attenuation not to exceed that obtained with 1mm of aluminum.

The present invention makes use of graphite fibres, alone or in combination with organic fibres in a plastics resin matrix as a skin around a rigid polyurethane foam or other foamed plastics core to provide a sandwich constructed couch suitable for supporting patients for examination on a rotational therapy simulator and yet having a uniform transparency to X-rays in such a manner as to permit examination of the patient by the X-ray passing through the patient and the supporting structure while using reduced doses of X-rays.

It is a feature of one object of the invention to provide a diagnostic or therapy stretcher which has high strength to weight ratio and high flexural rigidity.

It is a feature of another object of the invention to provide a diagnostic or therapy stretcher wherein the structure has a relatively high and uniform transparency to X-rays and gamma rays.

It is a feature of yet another object of the invention to provide a diagnostic or therapy stretcher which is particularly advantageous in enabling a beam of X-rays to be directed to the plane of the stretcher at an oblique angle without presenting a substantial variation in the transmission of X-rays.

In accordance with the aforementioned features the invention in its broadest aspects comprises graphite or carbon fibres alone or in combination with organic fibres disposed in an epoxy matrix to form a skin around and bonded to a rigid polyurethane foam core thereby defining a sandwich construction.

The invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 is an isometric drawing, partially sectioned view of a diagnostic stretcher, and

FIG. 2 is a base for receiving the stretcher shown in FIG. 1.

Referring now to FIG. 1, the diagnostic stretcher is generally indicated at 1 and comprises an outer skin 10 formed of carbon (graphite) fibres alone or in combination with PRD-49 organic fibres manufactured by Dupont (Trademark). The fibres are formed in an epoxy matrix to form a skin around and bonded to a rigid polyurethane foam core 12 to provide a structure of sufficient thickness to support a patient in a cantilevered position and suitable for examination on a rotational therapy simulator yet possessing a relatively high and uniform transparency to X-rays so as to meet the attenuation requirements of the regulations. Integrally bonded to the bottom surface of tray 10 is a sheetlike rigid tray 13. Tray 13 extends longitudinally over only a minor portion of the stretcher 1 and slidably cooperates with a channel-shaped carrier 14 suitably mounted on the top surface 2.sup.a of the support base 2. While forming no part of the present invention, tray 13 may be slidably secured to carrier 14 by a plurality of mushroom head bolt members 15, or any other conventional fastening members. In any event, stretcher 1 is supported in cantilever fashion by base 2. The improved performance of the stretcher is the result of using high-strength, high-modulus fibres having relatively high transparency to X-rays and gamma rays which permit the using of less material to achieve the desired structural stiffness. As mentioned above, this results in a stretcher having X-ray attenuation less than that obtained by passing X-rays of about 90 kvp through 1 mm of aluminum.

The invention enables the construction of a couch of desirable cross-section (i.e. width, depth and shape) which benefits from three essential properties of fibres, that is, high-strength, high-modulus and high transparency to X-rays.

The invention further provides for reduced attenuation to X-rays and gamma rays which is achieved by using less material to absorb such X-rays and gamma rays and by using a material which is more transparent to X-rays.

Other embodiments of the invention falling within the terms of the appended claims will occur to those skilled in the art.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A diagnostic stretcher, substantially transparent to X-radiation, with an attenuation equivalent to less than 1 mm of aluminum when subject to X-rays of 90 kvp passed normal through the said stretcher, said stretcher comprising:

i. an outer skin of carbon or graphite fibres in epoxy matrix, said skin having a configuration of a long thin and substantially flat board suitable for receiving a patient thereon and for cantilevered mounting on a stand, and

ii. a rigid polyurethane foam core within said skin, said skin and core being bonded together.

2. A diagnostic stretcher in accordance with claim 1 wherein said outer skin additionally includes organic fibres.