Patent Description:
Many radiotherapy apparatuses include a radiation source mounted on a gantry arm that is rotatable around a patient support on which a patient can be placed for treatment. The source is mounted at the end of the gantry arm, oriented so that the beam that it produces is directed towards the axis of rotation. The beam may be collimated by a collimator which is also mounted at the end of the gantry arm.

The point at which the centre of the beam meets the axis is known as the "isocentre". Thus, as the drum rotates, the beam arrives at the isocentre from all angular directions within a vertical plane. This allows a sufficient dose to be delivered to a target volume while minimising the dose delivered to surrounding healthy tissue.

The radiation head may need to be accessed by a maintenance engineer for, for example, maintenance or repair.

<CIT> teaches a system for a CT apparatus, the cover of which being held closed by default due to gravity or spring-operated forces.

Aspects and features of the present invention are described in the accompanying claims.

Specific embodiments are described below by way of example only and with reference to the accompanying drawings in which:.

In radiotherapy it is important to take steps to reduce patient discomfort to improve the patient's experience. It is also important to lower patient anxiety, since stress is damaging to patient health and may negatively affect the radiotherapy treatment. Seeing the radiation source and other components, such as the collimators, may be intimidating to the patient and cause the patient stress. Therefore, in device of the present disclosure a cover is attached to the arm to conceal the components in the radiation head.

Since the radiation head includes a lot of compact components, the head may need to be accessed for servicing, maintenance, replacement or repair by an engineer. When an engineer visits a treatment site to service, maintain, repair and/or replace components in the radiation head, the machine cannot be used for treatment. This is, therefore, machine 'downtime'.

To access the radiation head the engineer must remove the cover. Time spent removing the cover increases the downtime of the machine. Typically removing components on a radiotherapy device is time consuming since the components are fixedly attached. Removing components may require a lot of man power and/or specialist tools.

The easy-open cover in the present disclosure can be opened by a single user with little effort. A single maintenance engineer can open the cover quickly and freely work on the radiation head whilst the cover is held in the open position. The radiation head can be accessed easily and quickly, reducing machine downtime.

Throughout the figures, like reference numerals are used to indicate like parts.

In <FIG> a radiotherapy apparatus comprises a radiation head <NUM> comprising a source of radiation which emits a beam of radiation along a beam axis <NUM>. The source is mounted on an arm <NUM> which is itself supported by a rotatable drum <NUM>. The drum <NUM> may also be referred to as a gantry. The drum is arranged to rotate about a central axis <NUM> carrying with it the arm <NUM> and the source.

The arm <NUM> is mounted to the drum <NUM> so as to support the source at a location offset from the rotation axis <NUM> but pointing towards the rotation axis <NUM>. The location at the meeting point of the beam axis <NUM> and the rotation axis <NUM> is referred to as the "isocentre". Thus, as the drum <NUM> rotates, the source rotates around the isocentre, directing a beam toward that isocentre continuously. The beam <NUM> can be delivered to the patient from all angles, allowing a sufficient dose to be delivered to a target volume while minimising the dose delivered to surrounding healthy tissue.

The arm <NUM> rotates though degrees of rotation along a rotation path. The arm at the top most point is defined as <NUM>° of rotation, and the arm at the bottom most point is defined as <NUM>° rotation.

<FIG> shows a side view of a radiotherapy apparatus <NUM> according to the present disclosure. The apparatus comprises a radiation head <NUM>. The radiation head is configured to produce a beam of therapeutic or imaging radiation. The beam may be collimated (i.e. shaped) in accordance with a treatment plan. The radiation head may include a collimator, such as a multileaf collimator, for collimating the beam.

The radiation head is used to refer to the end of the arm which houses the radiation source, any collimation devices and any other components used for producing the radiation beam. The radiation source may be a linear accelerator, in which charged particles, such as electrons, are accelerated along a waveguide towards a target to produce therapeutic radiation. Housing is used to refer to the components of the radiotherapy apparatus which do not include the source of radiation or any collimation devices. That is, the housing is the structure, covers and associated features which provide the mechanism and support for a source of radiation to be used to deliver a beam of radiation according to a treatment plan.

The radiation head <NUM> is supported on an arm <NUM>. The arm bears the weight of the radiation head and supports the radiation head. The arm <NUM> is attached to a drum <NUM>. The drum <NUM> is configured to rotate around a central axis, carrying with it the arm <NUM>. The rotation of the arm <NUM> causes corresponding rotation of the radiation head <NUM>. In this way, radiation can be delivered to the patient from a plurality of angles. The drum may be able to rotate through <NUM>°, or may be able to rotate through a smaller range, such as <NUM>° or <NUM>°. The arm has a fixed upper casing <NUM>. This covers the outer side of the arm. The upper casing does not cover the radiation head <NUM>.

The arm <NUM> and the drum <NUM> are a 'support structure' which support the radiation head and other components of the radiotherapy apparatus. The arm and the drum are fixed relative to one another.

The arm <NUM> has a near end, which is the end attached to the drum <NUM>. The far end of the arm <NUM> is the end distal from, i.e. away from, the drum <NUM>. Features are discussed throughout as being attached at or towards the near or far end. This language is used to refer to attachment towards the near or far end respectively. That is, it could refer to a point at the furthest end, alternatively could refer to a point near to the end. It could refer to a point anywhere in the half of the near/far end.

A cover <NUM> is attached to the arm <NUM>. In <FIG> the cover is shown in a closed position in which it conceals the radiation head <NUM>. The cover may be made from glass reinforced plastic, GRP.

In the closed position the cover <NUM> forms a façade over the radiation head <NUM>. That is, the cover blocks the radiation head from the view of the patient. The cover may cover all, or part, of the radiation head <NUM>.

The cover is used to, as described above, conceal the components of the radiation head from the view of the patient. Additionally, the cover shields the components of the radiation head from the exterior environment. For example, the cover protects the source of radiation from dust or other particles in the treatment room. The cover therefore covers the components of the radiation head to conceal or shield the components from the view of the patient and to protect or shield the components from the exterior environment. The term shield is used to describe covering, or at least partially covering.

The arm <NUM> is positioned on the drum <NUM> radially outwards from the cover <NUM>. That is, the cover <NUM> is positioned on the inside edge of the arm <NUM>.

The cover is hingably attached to the support structure, for example the arm <NUM> or to the drum <NUM>, at a first attachment point. The cover is attached to the drum or to the near end of the arm at the first attachment point by a hinge <NUM>. An example of a hinge is discussed is more detail below in relation to <FIG>. The first attachment point is on the support structure, meaning that the first attachment point is at a fixed location relative to the arm <NUM>.

A locking mechanism <NUM> (or "lock" <NUM>) connects the cover <NUM> to the arm <NUM> at a second attachment point. The locking mechanism is positioned at or near the distal end of the arm (i.e. the opposing end of the arm to the hinge <NUM>). The locking mechanism <NUM> releasably attaches the cover <NUM> to the arm <NUM> at the second attachment point. When the locking mechanism is locked, the cover <NUM> is attached to the arm at two locations (i.e. the first and second attachment points) and therefore is held fixedly relative to the arm <NUM> in a position which conceals the radiation head <NUM>. When the locking mechanism is released, the cover <NUM> is released from, and no longer attached to, the arm <NUM> at the second connection point. An example of a locking mechanism <NUM> is described in more detail below in <FIG>.

In the locked state, in which the cover is closed, the connection is secure enough such that the cover <NUM> is secured to the arm <NUM> at all degrees of rotation of the arm <NUM> (i.e. the connection is secure enough to overcome the force of gravity). Further, the cover is held securely in the closed position and does not open upon rotation of the arm <NUM> around the centre axis, even when the arm <NUM> is rotated at relatively high speeds which are necessary during treatment. Therefore the cover will not open when the radiotherapy apparatus is in use, for example when a patient is being treated with therapeutic radiation. During treatment the cover is in the closed position and the components of the radiation head are shielded from view of the patient by the cover. This provides a less intimidating environment for the patient, which improves the patient's wellbeing.

The lock and hinge in the figures are illustrated as being positioned at the far end and the near end of the arm respectively. However, the lock and hinge may be positioned anywhere on the support structure to provide the necessary function. For example, the hinge could be positioned on the longitudinal side of the arm/cover such that the cover hinges open along the longitudinal side of the arm/cover. The lock mechanism may be positioned on the opposite longitudinal side of the arm/cover to the hinge.

In some examples the lock may be combined with the hinge, such that the hinge can be locked in the closed position, which in turn locks the cover in the closed position. That is, the hinge is fixable or lockable into a fixed position.

There may be times when the radiation head <NUM> needs to be accessed. This may be for maintenance, or servicing, such as testing to ensure all components are correctly functioning. When, for whatever reason, access to the radiation head is needed, the cover <NUM>, which is in place to cover the components of the radiation head, prevents the engineer from directly accessing the radiation head. The cover must be moved or removed in order to provide access to the components in the radiation head.

As explained above, time spent removing the cover increases the downtime of the machine.

In the present apparatus, to access the radiation head <NUM> the cover <NUM> is moved from the closed position (in which the radiation head is concealed or covered by the cover) to the open position, in which the components of the radiation head are accessible to a user or operator. The cover <NUM> is a quick release cover. That is, the cover can be opened easily and without the need for tools or equipment. This is labour saving, and saves man power required to access the radiation head. Further, the radiation head can be accesses quickly, which reduced machine downtime for maintenance and repair.

Therefore, the cover <NUM> can be opened quickly.

In addition, the cover can be removed if necessary. To remove the cover <NUM>, the hinge <NUM> is dismantled. In the device illustrated in the figures the hinge <NUM> is a hinge pin. To remove the cover completely, the pin is removed from between the hinged parts, allowing the hinged parts to be separated and the cover <NUM> to be completely removed from the arm <NUM>.

In some aspects, the radiotherapy apparatus has a head touch guard ring and head ending cover <NUM>. This ring covers the radiation head. The ring is positioned over the radiation head and external to the cover <NUM>. In devices having the guard ring, the ring is removed before the cover <NUM> is opened.

The guard ring is a proximity sensor for the radiotherapy device. If an object contacts the guard ring, or comes within a set threshold distance of the guard ring, a signal is sent to a control system to initiate a shut-down of the radiotherapy device. The object could be a patient or component of the radiotherapy device. In shut-down the control system stops the radiotherapy device from moving or delivering treatment. Therefore the guard ring acts as a safety measure to mitigate the treatment arm colliding with a patent or other object.

<FIG> shows the radiotherapy apparatus of <FIG> with the cover in the open position. The radiation head is in the <NUM>° position, i.e. at its highest point and directed substantially vertically downwards.

The cover <NUM> is attached to the arm <NUM> and /or the drum <NUM> by the hinge <NUM>. The hinge is in the open position such that the cover is angled relative to the arm (i.e. there is an angle between the cover <NUM> and the arm <NUM>).

In the open position the cover <NUM> and the arm <NUM> are not connected at the second connection point. The cover has been moved downwards, i.e. away from the arm. The radiation head <NUM> which is shielded by the cover in the closed position, is exposed in the open position. Components of the radiation head are therefore accessible.

To move the cover from the closed position to the open position, the lock <NUM> is unlocked. The lock can be unlocked by a user, for example by a maintenance engineer. The lock <NUM> can be a quick release lock, meaning it can be unlocked with a single, or with a simple, application of pressure from the user.

In the lock shown in the figures, the lock <NUM> is includes locking parts 214a and 214b which are integral to, or fixedly attached on, the arm <NUM> and the cover <NUM> respectively. The lock <NUM> has a locked position in which the locking parts 214a and 214b are securely fastened together. Since the locking parts 214a and 214b are positioned on the arm <NUM> and the cover <NUM> respectively, when the lock is in the locked position the arm and the cover are held together securely. This is the closed position (shown in <FIG>) in which the radiation head <NUM> is concealed by the cover <NUM>. In the open position the parts are not securely held together, such that the parts 214a and 214b may be separated and the cover <NUM> is not securely held to the arm <NUM> at the second connection point. The cover <NUM> is secured at the near end to the drum <NUM> or to the arm <NUM> by the hinge <NUM>, and at the far end the cover <NUM> is not secured to the arm <NUM>. With the radiation head in the <NUM>° position, i.e. at its highest point and directed substantially vertically downwards, gravity acts to move the cover <NUM> away from the arm <NUM>. With the radiation head <NUM> in the <NUM>° position, the arm is at the top of the rotation path, and the cover <NUM> is positioned below the arm <NUM>. Therefore the cover <NUM> can move away from the arm <NUM> due to the downwards force of gravity.

In the <NUM>° position, gravity acts on the cover <NUM>. The cover <NUM> is secured at the near end to the drum <NUM> or to the arm <NUM> by the hinge <NUM>, but is not secured to the arm <NUM> at the far end with the lock <NUM> is in the unlocked position. Gravity acts on the cover <NUM> such that the cover rotates away from the arm <NUM> around the hinge <NUM>, revealing the radiation head <NUM>. In the open position the cover <NUM> is at an angle relative to the arm <NUM>.

As the cover <NUM> opens, it rotates on hinge <NUM>. The angle of rotation of the cover <NUM> about the hinge <NUM> increased as the cover <NUM> opens more widely, and as the far end of the cover <NUM> moves further from the far end of the arm <NUM>. The 'angle' of the cover is used to describe the angle at which the cover rotates open relative to the arm. It is illustrated as α on the figures. In the closed potion, alpha is zero. In the open position, alpha could be, for example, <NUM>° or <NUM>°. With the cover <NUM> in the open position the radiation head <NUM> is accessible to a user. That is, cover <NUM> does not conceal the radiation <NUM> head when in the open position. The radiation head can therefore be accessed by a maintenance engineer for maintenance, service or repair.

When the user no longer needs to access the radiation head, for example when the radiation head has been repaired or serviced, the user can close the cover <NUM> by moving the far end of the cover towards the arm <NUM>. When the far end of the cover <NUM> is fully closed and touches the arm <NUM>, the lock <NUM> is locked to secure the cover <NUM> to the arm <NUM> at the far end to maintain the cover <NUM> in the closed position. The lock <NUM> may automatically lock (i.e. move to the locked position) upon contact of the far end of the cover <NUM> with the arm <NUM>. Alternatively, the user may physically lock the lock <NUM> to secure the ends together. In this locked position the cover <NUM> is secured in the closed position and the radiotherapy apparatus can be used for treating patients.

In the above embodiment the cover <NUM> moves to the open position using the force of gravity. When the device is in the <NUM>° position, with the radiation source at the top and pointing vertically downwards, the cover <NUM> is beneath the arm <NUM> and therefore can be hinged away from the arm using the force of gravity.

There may be occasions when access to the radiation head is required when the device is at the <NUM>° position. There may be operations which require the device to be in the <NUM>° position. Some operations (e.g. repair or maintenance) may be easier with the device in this position. In this position the arm <NUM> is at the bottom of the rotation path. The radiation source is therefore at the bottom and is pointing vertically upwards. In the <NUM>° position, the cover <NUM> is above the arm <NUM>. Therefore gravity acts to pull the cover down on to and towards the arm <NUM>. In this position gravity therefore will not cause the cover <NUM> to move to the open position, even if the lock <NUM> is unlocked.

<FIG> shows the radiotherapy apparatus <NUM> in the <NUM>° position.

To provide an apparatus which allows a user to access the radiation head more easily and without the need for additional man power, an optional additional feature can be included in the radiotherapy apparatus. The features assist the user when pushing the cover <NUM> up and away from the arm <NUM> into the open position.

The apparatus can also include a spring mechanism <NUM>. In the figures the spring mechanism is an air spring. However, any suitable spring could be used.

The spring <NUM> is fixedly attached at one end to the arm <NUM> and is fixedly attached at the opposing end to the arm <NUM>. The spring can be positioned anywhere along the length of the cover. That is, it could be positioned anywhere between the hinge <NUM> and the far end of the cover. The spring mechanism <NUM> is configured to bias the cover <NUM> away from the arm <NUM> by providing a biasing force between the cover <NUM> and the arm <NUM>.

The spring <NUM> provides an outwards biasing force between the arm <NUM> and the cover <NUM>. That is, the spring biases the cover <NUM> towards the open position. If the lock <NUM> is in the unlocked state (that is, if the cover is not attached to the arm at the far end) the spring will then provide a force which will move the cover from the closed position to the open position. Depending on the strength of the spring, it may not exert enough force to move the cover to the open position, however it will exert a force biasing the cover <NUM> into the open position, so a user only needs to provide the additional force (the delta) to open the cover. That is, the spring makes it easier for the user to open the cover by reducing the force required by the user.

When a spring is compressed from its resting position, it exerts an opposing force. When a spring is at its resting position, it no longer exerts a force.

The spring <NUM> in <FIG> provides a biasing force between the cover <NUM> and the arm <NUM> up to a certain angle of rotation of the cover <NUM> about the hinge <NUM> at which the spring has reached its resting position. The system uses a spring which has a resting position that corresponds to the cover <NUM> being open in the optimal position to allow the radiation head to be accessed. This optimal position is the open position. The spring <NUM> provides a biasing force up to an angle of rotation at which the cover <NUM> is in the open position, after which is does not provide further rotation.

The angle of rotation of the cover <NUM> about the hinge <NUM> is alpha in the figures, and is described as the open angle.

In the figures the spring <NUM> has a resting position which corresponds to an open angle of <NUM>°. Therefore, when the cover <NUM> opens to an angle of <NUM>°, the spring no longer exerts a biasing force in the opening direction. The cover <NUM> will stop opening once it has reached <NUM>°. This angle is optimal to provide access to the radiation head whilst not being too far open that it becomes difficult to close the cover <NUM> again.

In other examples the resting position of the spring <NUM> may correspond to an open angle of between <NUM>° and <NUM>°. In other examples, the open angle is between <NUM> and <NUM>°. In further examples the open angle is between <NUM> and <NUM>°. Other open angles can be envisaged, and the optimal open angle may vary depending on the dimensions of the specific device.

In one example two springs <NUM> used, one spring positioned on each side of the arm <NUM>. This provides a higher opening force to the cover. In other examples, there is a single spring <NUM> attached on only one side of the arm <NUM>. In other examples still, there are no springs on the device.

In use, when the locking mechanism <NUM> is unlocked, the far end of the cover <NUM> is not attached to the far end of the arm <NUM>. The spring mechanism <NUM> pushes the cover <NUM> away from the arm <NUM>. The cover <NUM> rotates around the hinge <NUM> into the open position to provide access to the radiation head.

In <FIG>, when the lock <NUM> is unlocked, the spring mechanism <NUM> provides the force necessary to push the cover <NUM> up and away from the arm <NUM>. That is, the spring provides the force to overcome gravity and therefore cause the cover <NUM> to move into the open position. This means that the user operating the device does not have to move the cover between the open position and the closed position.

The spring <NUM> provides a biasing force to open the cover <NUM> to an optimal open angle alpha α. This can reduce user errors and possible damage to the device since the cover <NUM> automatically opens to the correct degree.

In some examples the spring <NUM> instead provides a force less than the force required to overcome gravity. However the biasing force will nonetheless assist the user by providing an amount of biasing force towards the open position, meaning the amount of force required by the user to open the cover is reduced.

When access to the radiation head <NUM> is no longer required the cover is closed. To close the cover <NUM> when the device <NUM> includes a spring <NUM>, the user must push the cover with enough force to overcome the outward bias of the spring, and therefore push the cover back towards the arm and into the closed position.

Further, another optional feature is illustrated in the figures. A strut, <NUM>, described in more detail in relation to <FIG>, is movable between a stowed position and an erect position. The strut is in stowed position when the cover <NUM> is in the closed position. When the cover is in the open position, the strut is moved into the erect position. In the erect position, the strut is attached at either end to the cover <NUM> and to the arm <NUM>. The strut therefore 'props' the cover <NUM> open. The strut <NUM> takes the weight of the cover <NUM> when open to maintain it in the open position.

This is advantageous to the user accessing the radiation head <NUM>, since the user does not need to hold the cover open whilst accessing the head. The cover <NUM> is supported in the open position by the strut. The strut is attached between the cover and the arm so that the cover can be held open even if the gantry or drum <NUM> is rotated to a different angle of rotation. This might be necessary when performing maintenance on the radiation head. The strut <NUM> is strong enough to maintain the cover <NUM> in the open position even whilst the arm <NUM> rotates.

Specific details of an example of the strut are described in more detail below in relation to <FIG>.

The strut <NUM> and the spring mechanism <NUM> are both optional features. One aspect of the disclosure includes a radiotherapy apparatus with neither the strut not the spring mechanism. In another aspect, the radiotherapy apparatus includes a strut and/or a spring mechanism.

In the aspect which includes both a strut <NUM> and a spring mechanism <NUM>, the cover <NUM> opens as follows:
The user unlocks lock <NUM>, such that the far end of the cover <NUM> and the arm <NUM> are not connected. The spring mechanism <NUM> biases the cover <NUM> into the open position and the cover rotates around hinge <NUM>. Further, the springs limit the open angle. The spring <NUM> opens the cover to the open angle of <NUM>°. The user moves the strut to the erect position. In the erect position the strut is fixed between the open cover <NUM> and the arm <NUM>. The strut maintains or locks the cover <NUM> in the open position, such that the cover <NUM> does not move relative to the arm <NUM>. The user can then access the radiation head <NUM>. Only one user is needed to open the cover, and the user can perform the operations on the radiation head with both hands, since the cover is held open and the user does not need to hold the cover open.

When access to the radiation head is no longer required, the strut can be moved from the erect position into the stowed position. With the strut <NUM> in the stowed position the cover can be closed by exerting a force grater than the biasing force into the the closed position. The lock <NUM> is then locked to fix the cover <NUM> in the closed position.

Example components of the radiotherapy apparatus are described below in detail. It will be understood that these are specific examples of the components, and that any component suitable for carrying out the function of the component can be used in the radiotherapy apparatus.

<FIG> shows an example hinge <NUM>. The hinge has a first hinge part 212a which is fixedly attached to the drum <NUM>. The hinge has a second hinge part 212b which is fixedly attached to the cover <NUM>. The first part and the second part are held together by a pin <NUM>. The first part can rotate around the pin relative to the second part. The cover <NUM> can rotate relative to the drum <NUM> around the pin. In this way, the cover moves from the closed position and the open position.

In another example, the first hinge part 212a is fixedly attached to the arm <NUM> and the second hinge part 212b is fixedly attached to the cover <NUM>.

Any hinge mechanism which hingably attaches the cover relative to the arm (i.e. directly to the arm or to a component which is fixably attached relative to the arm) can be used.

In the embodiment in the figures, a single hinge <NUM> is used to connect the cover to the arm. In another example, two hinges are used. In the example, the two hinges are positioned asymmetrically, such that when the lock <NUM> is unlocked, the cover <NUM> initially opens to a small angle, before opening to the full open angle.

<FIG> shows example brackets <NUM>. The brackets are attached between the cover <NUM> and the arm <NUM> and support the movement of the cover between the closed position and the open position. The brackets <NUM> may further impart an upper limit on the degree to which the cover <NUM> can open relative to the arm <NUM>. That is, when opening the cover <NUM> there is an open angle beyond which the cover cannot further rotate away from the arm due to the limitation provided by the brackets.

In one example brackets are positioned between the cover <NUM> and the arm <NUM> on both sides of the arm <NUM>. This provides maximum support to the cover <NUM> between the open and the closed positions. In other examples, there is a bracket <NUM> attached on only one side of the arm <NUM>. In other examples still, there are no brackets on the device.

The cover <NUM> is fixed on arm <NUM> by brackets <NUM>. The brackets <NUM> provide an attachment point between the arm <NUM> and the cover. This attachment is stronger than the attachment provided by the hinge <NUM> and the lock <NUM>. The brackets therefore strengthen the attachment of the cover <NUM> to the arm <NUM>.

Brackets <NUM> each include a first part fixedly attached to the arm <NUM> and a second part fixedly attached to the cover <NUM>. In the closed position the first and second parts align and are secured together by a bolt <NUM>. To move the cover to the open position, the bolt <NUM> is removed such that the first and second parts of the bracket are no longer attached together. The bolt <NUM> can be accessed and removed by the user from the exterior of the cover <NUM>. The cover <NUM> is then free to move away from the arm <NUM> into the open position.

<FIG> shows an example lock <NUM>. The lock <NUM> is includes locking parts 214a and 214b which are integral to, or fixedly attached on, the arm <NUM> and the cover <NUM> respectively. The lock <NUM> has a locked position in which the locking parts 214a and 214b are securely fastened together by fastener <NUM>. Since the locking parts 214a and 214b are positioned on the arm <NUM> and the cover <NUM> respectively, when the lock is in the locked position the locking parts, and therefore the arm and the cover, are held together securely. This is the closed position (shown in <FIG>) in which the radiation head <NUM> is concealed by the cover <NUM>.

In the open position the parts are not securely held together, such that the cover can be moved into the open position as described above. The lock may include a pin <NUM> to hold together the parts. To unlock the lock, the pin is removed and the parts can be separated. To lock the lock, the pin is inserted between the parts thereby securing them together. Any type of conceivable lock <NUM> for securely locking the cover to the arm could be used.

<FIG> shows an example strut <NUM>. The strut <NUM> has a first end 218a which is hingably mounted to the arm <NUM>. That is, the strut can rotate relative to the arm <NUM>. The strut <NUM> also has a second end 218B which is configured to attach to a point <NUM> on the cover <NUM>. In the closed position the strut <NUM> is not attached at the second end 218b to the cover <NUM>, and is stowed to fit in between the closed cover <NUM> and the arm <NUM>. When the cover <NUM> is moved to the open position, the strut <NUM> can be rotated relative to the arm <NUM> to meet the cover <NUM>. The second end 218b is attached to the point <NUM> on the cover <NUM>. The strut <NUM> holds the cover <NUM> in the open position.

The strut therefore 'props' the cover <NUM> open. The strut <NUM> takes the weight of the cover <NUM> when open to maintain it in the open position. This is advantageous to the user accessing the radiation head <NUM>, since the user dos not need to hold the cover open whilst accessing the head. The cover <NUM> is supported in the open position by the strut. The strut is attached between the cover and the arm so that the cover can be held open even if the gantry or drum <NUM> is rotated to a different angle of rotation. This might be necessary when performing maintenance on the radiation head. The strut <NUM> is strong enough to maintain the cover <NUM> in the open position even whilst the arm <NUM> rotates.

<FIG> and <FIG> show the cover in the open position with the gantry at <NUM>° and at <NUM>° respectively. However, it will be understood that the cover <NUM> can be opened with the gantry at any angle of rotation (i.e. from <NUM> to <NUM>°). The radiation head may need to be accessed with the gantry at a specific angle - either for maintenance or servicing processes, or the radiation head <NUM> may need to be accesses is the gantry is stuck at a certain angle.

The radiation head <NUM> can be accessed with the gantry at any angle of rotation using the same opening mechanism as described above in <FIG> and <FIG> with the gantry at <NUM> and <NUM>° respectively.

The easy open cover in the present disclosure can be opened by a single user with little effort. This reduces man power. A single maintenance engineer can open the cover and freely work on the radiation head whilst the cover is help in the open position. Removing the cover does not require undoing bolts and unscrewing screws, and moving heaving parts, for example a large cover, around. Therefore radiation head can be accessed easily by a single user.

It is quick to access the radiation head with the cover described above. Reducing the time to access the radiation head reduces machine downtime. This reduces cost and increases efficiency.

Finally, the easy open cover provides a safe way to access the radiation head without causing damage to the radiotherapy apparatus. Removing the cover does not require moving heavy parts, and therefore reduces the risk of injury to the user.

Claim 1:
A housing system for a radiotherapy apparatus, the system comprising:
a support structure configured to support a source of radiation;
a cover hingeably attached to the support structure and movable between a closed position in which the cover shields the source of radiation and an open position; and
a lock configured to releasably lock the cover in the closed position.