WO2013120795A2

WO2013120795A2 - Brachytherapy system & in vivo dose detector therefor

Info

Publication number: WO2013120795A2
Application number: PCT/EP2013/052652
Authority: WO
Inventors: Robert Price
Original assignee: City University
Priority date: 2012-02-15
Filing date: 2013-02-11
Publication date: 2013-08-22
Also published as: GB201420171D0; WO2013120795A3; GB201202622D0; GB2515714A

Abstract

An in-vivo dose detector (41) for an HDR brachytherapy system, the detector comprising first and second sensors (55) that are operable to detect radiation from a source used to irradiate a tissue to be treated in the course of an HDR brachytherapy treatment, wherein said sensors (55) are arranged in said detector (41) so as to be differently orientated from one another.

Description

BRACHYTHERAPY SYSTEM & IN VIVO DOSE DETECTOR THEREFOR

FIELD

This invention relates to brachytherapy treatment systems, particularly but not exclusively to high dose rate brachytherapy treatment systems. Other particularly preferred embodiments of the present invention relate to in vivo dose detectors for such systems.

Illustrative embodiments of the present invention will hereafter be described with particular reference to high dose rate brachytherapy treatments for anal or rectal tumours. However, it will be appreciated that the teachings of the present invention are applicable to other brachytherapy treatments (such as conformal brachytherapy and pulsed-source brachytherapy for example) and to the treatment of other conditions, and as such the following detailed description should not be construed as limiting the scope of the present invention.

BACKGROUND Brachytherapy, as is well known in the art, is a type of radiation therapy in which radioactive materials (variously referred to hereafter as "seeds" or "sources") are placed in close proximity to, and often in direct contact with, the (typically malignant) tissue being treated. In very general terms, there are two currently practised brachytherapy treatments: low dose rate (LDR) treatments and high dose rate (HDR) treatments.

In low dose rate (LDR) treatments, sources with a relatively low radioactivity are permanently implanted within a tissue to be treated and left there to irradiate the tissue over the weeks and months following the implantation. In high dose rate (HDR) treatments, more highly radioactive sources are advanced into a tissue to be treated for a relatively short period of time, and then withdrawn from the patient once the treatment plan for that patient has been completed.

Brachytherapy treatment is appropriate for a variety of different conditions, including inter alia, prostrate tumours, breast tumours, lung cancer, oesophageal cancer, gynaecologic cancers (such as cervical cancer), anal/rectal tumours, sarcomas and head or neck cancers.

By way of illustration of the need for appropriate treatments for such conditions, in the UK over 10,000 patients per year are diagnosed with cancer of the rectum, and over 30% of the patients who have operable tumours subsequently require the use of a colostomy bag for the rest of their life.

Increasingly HDR brachytherapy is used to treat cancer of the rectum, in some instances before conventional surgical procedures are undertaken, and more recently an alternative to those surgical procedures (each of which has inherent risks associated with them). Recent studies of the use of HDR brachytherapy for the treatment of anal or rectal tumours have shown that the use of HDR brachytherapy can significantly reduce the likelihood of the patient having to be provided with a stoma.

In a commonplace HDR brachytherapy treatment (hereafter referred to simply as HDR brachytherapy), a plurality of catheters are inserted into the tissue to be treated, and a machine (known as "an afterloader") is controlled by computer to push a single relatively highly radioactive seed (for example of Iridium 192) into each of the catheters. The computer moves the seeds through the catheters in accordance with a patient treatment plan that has been carefully devised to provide an appropriate irradiation dose distribution for the tissue of the particular patient undergoing treatment. The plan defines (for each radioactive seed) a plurality of longitudinal positions within the catheter to which the seed will be moved (the so-called "dwell positions"), and the time that the seed will remain at each of those locations (the so-called "dwell time").

To implement the plan, the computer controls the afterloader to move each of the seeds to a first planned dwell position, to leave the seed at that position for the planned dwell time for that position, and then to move the source to the next planned position. This process is repeated until the dose distribution planned for treatment of the patient's tissue has been achieved.

A variety of systems have been developed to implement HDR brachytherapy, and an illustrative example of one such system is the so-called OncoSystem™ (sold by Nucletron UK Ltd (a Delft Instruments Company) of Nucletron House, Chowley Oak, Tattenhall, Chester CH3 9EX, United Kingdom). The OncoSystem™ consists of a bundle of Nucletron products for treating body- site specific cancers such as breast, rectal or gynecological cancers, and each bundle consists of OncoSmart™ applicators and disposables, and an Oncentra™ treatment control system.

The OncoSystem™ provides an accurate method of positioning sources inside the patient. However, a significant drawback of the system (and other like systems) is that measurement of the actual dose (as opposed to the planned dose) delivered to the patient is accomplished externally of the patient, and as such in a number of applications is necessarily somewhat inaccurate, principally because there is often a significant amount of tissue (often with varying radiation absorption properties) between the tumour and the skin.

The combination of technological complexity, a relatively large number of patients and the potentially hazardous nature of ionising radiation mean that there is a great potential for serious accident with potentially serious consequences if HDR brachytherapy is incorrectly delivered. To reduce, and preferably avoid, such problems - in particular damage to tissue surrounding the tumour being treated - it is important to know how much radiation is being delivered during treatment, and where that radiation is being delivered.

International PCT Patent Application Nos. WO2005/046794 and WO2008/009917 each disclose implantable brachytherapy probes (of different construction) that include radiation detectors for sensing the quantity and location of radiation being delivered to a patient during treatment.

Whilst the probes disclosed in these documents each provide a better alternative to external dose sensing, it remains the case that as the semiconductor radiation sensors employed in each instance have an asymmetric response to radiation (i.e. the sensors are relatively directional), the dosage readings acquired with each device tend to be less accurate than is desirable. A further problem is that as back-scattering of radiation occurs within the patient's body, the sensor outputs can exhibit low energy peaks that appear to be indicative of a high dose of radiation (and vice versa) thereby causing uncertainty in the determination of the actual radiation dose applied to the patient.

The present invention has been devised with the foregoing problems in mind. SUMMARY

To this end, a presently preferred embodiment of the present invention provides an in-vivo dose detector for an HDR brachytherapy system, the detector comprising first and second sensors that are operable to detect radiation from a source used to irradiate a tissue to be treated in the course of an HDR brachytherapy treatment, wherein said sensors are arranged in said detector so as to be differently orientated from one another.

As the detector of this embodiment includes two differently orientated sensors, the detector provides a more isotropic response to incident radiation than previously proposed detectors, an effect that can further be enhanced by summing the outputs of each sensor and computing an average dosage reading. In general terms, the teachings of the present invention provide that by employing a detector with a number (in this particular example, two) of differently orientated sensors, a more symmetrical response to incident radiation can be provided than has hitherto been possible with previously proposed detectors.

Another embodiment of the present invention relates to an intracavitary probe for an HDR brachytherapy system, the probe comprising: a holder having a plurality of smaller bores into each of which a catheter may be inserted and a further larger bore into which a detector array or a detector as described herein may be inserted, the probe being configured to hold said catheters and said detector/array in a predetermined positional relationship to one another.

A further embodiment of the invention relates to an HDR brachytherapy system comprising: a first catheter insertable into a tissue to be treated, and through which a radioactive source can be moved by an afterloader to irradiate the tissue at one or more dwell positions set out in a treatment plan; an in vivo dose detector as described herein movable to a detection position within said tissue to be treated; and means for measuring radiation detected by the detector when the detector is in said detection position and said source is in said one or more dwell positions.

Another embodiment relates to an HDR brachytherapy system comprising: an intracavitary probe as described herein; a catheter inserted into one of said smaller bores, and through which a radioactive source can be moved by an afterloader to irradiate tissue at one or more dwell positions set out in a treatment plan; a detector or a detector array as described herein provided in said larger bore; and means for measuring radiation detected by the detector/array when the source is in said one or more dwell positions.

Other presently preferred embodiments of the present invention, and features and advantages of all the embodiments described herein, are set out below in the detailed description of preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Presently preferred embodiments of the present invention will now be described, by way of illustrative example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of a prior art HDR brachytherapy system;

Fig. 2 is a schematic representation of an Oncosmart™ Intracavitary HDR brachytherapy rectal probe;

Fig. 3 is a schematic representation of an HDR brachytherapy system according to a preferred embodiment of the present invention;

Fig. 4 is a schematic representation of a detector;

Figs. 5(a) to 5(e) are schematic representations of the various steps in a method for producing a detector of the type shown in Fig. 4;

Fig. 6 is a flow diagram illustrating a mode of operation of the system;

Fig. 7 is a schematic representation of the proximal end (i.e. the collar end) of an intracavitary brachytherapy probe according to an embodiment of the present invention;

Fig. 8 is a schematic longitudinal cross-section of the probe along the line A— A in Fig. 7;

Fig. 9 is a schematic representation of a detector array in use with a probe of the type depicted in Fig. 7;

Fig. 10 is a schematic representation, in cross-section, of the proximal region of an intracavitary brachytherapy probe according to another embodiment of the present invention; Fig. 1 1 is a schematic representation, again in cross-section, of the proximal region of an intracavitary brachytherapy probe according to yet another embodiment of the present invention; and

Fig. 12 is a schematic illustration of the probe of Fig. 1 1 configured for use in a particular treatment regimen.

DETAILED DESCRIPTION

Referring now to Fig. 1 of the drawings, there is shown a prior art brachytherapy system 1 which comprises a computing resource 3, in this instance a PC, and an afterloader 5 which is operable to drive a set of radioactive sources (not shown) into and out of a bundle of catheters 7 that have been inserted into the region of tissue 9 of the patient that is to be treated. Prior to the HDR brachytherapy treatment, the position of the catheters 7 in the tissue is verified by any one of a number of imaging systems, for example by means of an ultrasound or x-ray imaging system.

The computing resource 3 controls the afterloader 5 in accordance with a treatment plan that has been devised under the supervision of a physician to deliver an appropriate dose of radiation to the tissue that is to be treated by HDR brachytherapy. The treatment plan consists, for each source that is to be inserted into the patient, a list of dwell positions (longitudinal positions within a given catheter to which the source is to be advanced) and a dwell time (a period of time for which the source is stationary at each dwell position) for each of those dwell positions. The treatment plan is carefully devised to deliver an appropriate dose at each position for the tissue to be treated 9, and the deliverance of this dose is typically verified by means of a detector 1 1 placed outside of the patient. The detector may, as shown, be coupled to a second computing resource 4 configured to monitor and record the dose detected by the detector. As will be appreciated, without the benefit of an in vivo detector at or near to the treatment site, preparation of the treatment plan requires calculation of the dose expected at the detector (not the dose applied at the treatment site), bearing in mind the extent and composition of any intervening tissue.

Fig. 2 is a schematic representation of an Oncosmart™ Intracavitary HDR brachytherapy rectal probe (available from Nucletron UK Ltd). The probe 13 consists of a plurality of catheters 15 (equivalent to the catheter bundle 7 of Fig. 1 ) which have been inserted into a sterile cylinder 21 which (in this instance) is to be inserted into the rectum of a patient. The catheters 15 have been fed through a numbered collar 17 which facilitates discrimination between catheters, and a support block 19 which abuts against the patient in use. In this instance eight catheters have been fitted through the collar and support into the cylinder, but a fewer or greater number of catheters may be employed if desired.

The sources, which are typically of Iridium 192, are of such a size that they can be advanced by the afterloader through the catheters, and depending on the size and shape of the tissue to be treated only a subset of the aforementioned catheters may have sources moved through them.

To measure the amount of radiation delivered to the tissue being treated from within the patient, close to the sites of radiation treatment, we have devised an in vivo dose detector 41 , shown schematically in cross-section in Fig. 4, that fits within a catheter 53 (in this particular instance, part of a 4 French catheter 53) and hence can be moved into and out of the probe and the tissue to be treated.

The detector 41 comprises a pair of sensors 55, differently orientated relative to one another, that are coupled to a suitable PCB 57, for example a flexible PCB of Kaplan. In one envisaged implementation each sensor 55 comprises a semiconductor diode configured to operate in a PV (photovoltaic) mode without an applied voltage bias, or with an applied bias. In other envisaged implementations, the detectors may comprise MOSFETs that have been specifically constructed to be radiation sensitive, or any other device (the like of which are well known to persons skilled in the art) that is responsive to radiation.

For the purposes of the following detailed description it will be assumed that the sensors each consist of a semiconductor diode used in photovoltaic mode. The sensors each include a pair of electrical contacts 59 that couple the p- 55(i) and n-type 55(ii) semiconductor regions to a suitable measuring device such as an electrometer 43 (shown schematically in Fig. 3). In this operating arrangement the electrometer measures charge per unit time and the diodes provide a linear response with respect to the applied dose. If the diodes were to comprise MOSFETs, for example, the electrometer would measure a voltage shift, and the MOSFETs could either be withdrawn and interrogated once treatment has been completed or - in a preferred embodiment - interrogated in real time.

The sensors 55 and the PCB 57 each include a plurality of so-called bump pads 61 , typically of silver, and as shown in Fig. 4 adjacent pairs of pads 61 have been joined to one another by a small layer of conducting material 63, such as gold. Spaces 65 between the sensors and the substrate have been backfilled with a relatively high strength epoxy resin, such as a silver epoxy resin, and the sensors and substrate have been encapsulated within the catheter by a black epoxy resin 67 that seals the sensors 55 from ambient light. The catheter 53 may also be provided with one or more locating rings (not shown) of known type, such as of nickel or titanium, so that it can be accurately located in images derived from whatever imaging system is being used to locate the catheter in the tissue to be treated.

As the detector 41 of this embodiment includes two discrete and differently orientated sensors 55, the detector provides a more isotropic response to incident radiation than previously proposed detectors, an effect that can further be enhanced by summing the outputs of each sensor and computing an average dosage reading. In general terms, the teachings of the present invention provide that by employing a detector with a number (in this particular example, two) of differently orientated sensors, a more symmetrical response to incident radiation can be provided than has hitherto been possible with previously proposed detectors.

Although this embodiment of the invention contemplates the incorporation of a single detector in a catheter, another embodiment of the invention contemplates the incorporation of a detector array in a catheter; each detector of the array being as depicted in Fig. 4. The detectors may be provided adjacent to one another in the catheter, or in another arrangement the sensors may be spaced from one another along the length of the catheter.

One illustrative method of constructing a detector of the type depicted in

Fig. 4 will now be described with reference to Figs. 5(a) through 5(e) of the accompanying drawings.

In a first step of the method, conventional grown p-n junction semiconductors with a relatively asymmetric response to incident radiation are thinned, for example by means of a conventional etching or dethinning process, to provide p-n junction semiconductors that are approximately 150 microns in height and have a more symmetrical response to incident radiation.

Bump pads 61 , typically of silver are fixed to the thinned semiconductor diode 55 and to the PCB 57 in a known manner, following which - as shown in Fig. 5(a) - a ball 62 of conducting material, for example gold, is provided on each of the diode bump pads (or alternatively to each of the bump pads 61 on one side of the PCB). Next, as shown in Fig. 5(b), a thin interface layer 64 of low strength conducting epoxy, for example of silver, is provided between the conducting balls and bump pads, and the diode 55 and PCB 57 are pressed together whilst being heated to approximately 130°C to cure the epoxy and couple the diode to the PCB. The next step, shown in Fig. 5(c) is to back fill the space 65 between the diode 55 and the PCB 57 with a high strength epoxy, and then cure that epoxy at approximately 80°C to enclose the junction between the diode 55 and PCB 57.

The resulting assembly is then inverted, as shown in Fig. 5(d), and a second diode 55 with bump pads 61 is procured. The second diode is provided with a ball 62 of conducting material, for example of gold, on each of the diode bump pads (or alternatively to each of the bump pads 61 on one side of the PCB), and a thin interface layer 64 of low strength conducting epoxy, for example of silver, is provided between the conducting balls and bump pads. The second diode and PCB are then pressed together whilst being heated to approximately 130 °C to cure the epoxy layer 64, and as will be appreciated by persons skilled in the art, care must be taken at this stage to ensure that the temperature remains below the point where the epoxy fixing the first diode to the other side of the PCB starts to melt. Once the second diode 55 has been fixed to the PCB 57, the space 65 between that diode and the PCB is back-filled with high strength epoxy, and then that epoxy is cured at approximately 80 °C.

In the final steps of the process, contact wires 59 (see Fig. 4) are fixed to each of the diodes, and the assembly is then fitted into a catheter and encased within the catheter by means of a light-tight black epoxy to provide a detector of the type depicted in Fig. 4.

Fig. 3 is a schematic representation of some of the functional components of a brachytherapy system 31 of a preferred embodiment of the present invention shown assembled for HDR brachytherapy of a tissue 9 to be treated.

As shown, a dose detector 41 has been inserted into one of the catheters 7, 13 which have been inserted into a tissue 9 to be treated. The detector of this illustrated embodiment comprises semiconductor diodes and is connected to an electrometer 43 that is configured to measure charge per unit time, and in the preferred arrangement the detector 41 remains in one known position within the tissue whilst the sources are moved relative to the detector through the catheters. As mentioned above, other types of sensor and voltage or charge measuring devices may be employed if desired.

Movement of the sources through the catheters is controlled by a known afterloader (not shown in Fig. 3) controlled by a computing resource (also not shown) in accordance with the treatment plan devised for treatment of the tissue to be treated.

The system includes a dose database 35 which interfaces with a treatment planning system 33 to load a treatment plan consisting of dwell positions "r" and dwell times "t" for each source that is to be employed. In the preferred embodiment, to ensure that it is not possible to overwrite or amend a given treatment plan that has been approved by a physician, the dose database 35 is configured to have read-only access to the treatment planning system.

The dose database 35 interfaces with a planned dose determinator 37 which calculates for each dwell position the planned dose D(r, t) associated with the source remaining at dwell position r for the associated dwell time t. The determinator 37 is also configured to calculate the integrated patient dose jD(r, t) which corresponds to the total dose applied to the tissue 9 thus far in the course of the HDR treatment. The dose determinator 37 is configured to output a signal representative of the planned dose for each dwell position and a signal representative of the planned integrated patient dose thus far in the HDR treatment.

Timing circuitry 39 is coupled to the dose database 35, and is configured to measure periods of time corresponding to the planned dwell times t at each dwell location for which the electrometer 43 measures (in this particular instance) the charge resulting from radiation detected by the detector 41 . The electrometer 43, which may be any of a variety of commonly available known electrometers, outputs a signal representative of the amount of charge Q measured for a given dwell position and dwell time t to a comparator 45 which compares Q(t) to D(r, t) to determine in real time whether the actual dose for a given dwell position corresponds to the planned dose for that position. The comparator may also be configured to compare the total measured dose thus far in the procedure with the planned total dose for that stage of the procedure.

The comparator 45 outputs a signal representative of the aforementioned comparisons to a reporting system 49 that is preloaded with a set of patient alert criteria 51 . These criteria define when an emergency condition is determined to have occurred, in response to which the procedure must be terminated and the sources withdrawn from the catheters. In one embodiment, the alert criteria may set dose thresholds for each dwell position which cannot be exceeded. In another embodiment, the alert criteria may be set such that the system monitors the actual dose as a function of time, and is configured such that the dose must be within a set limit, for example +/-5% Other arrangements will be apparent to persons skilled in the art.

In the event that an emergency condition is determined to have occurred, the sources are withdrawn and the procedure is terminated. Otherwise the reporting system logs the actual dose (optionally versus the planned dose) for each dwell position to provide the physician with an accurate representation of the dose at the dwell position as well as the total dose administered to the patient in the course of the treatment.

The functional components of Fig. 3 may be configured as stand-alone devices or functional software components. In an alternative arrangement one or more of these components may be integrated together. For example, in a preferred arrangement the timer, electrometer and comparator may be configured as a single application specific integrated circuit (ASIC) 47.

To ensure data integrity it is preferred, as mentioned above, that the treatment planning system is implemented by a first computing system, the controller for the afterloader is implemented by a second computing system, the reporting functionality is implemented by a third computing system and the detection functionality is implemented by a fourth computing system (communication between these systems being carefully controlled to ensure that there is no possibility of changes made in the detection or reporting system corrupting or changing data held in the HDR control system or the treatment planning system.

Whilst this is the preferred arrangement, it is of course conceivable that that the aforementioned ASIC may be integrated into a single computing resource operable to maintain the dose database, implement the dose determinator, and provide the reporting system functionality, and it is even conceivable that this computing resource may be that which is provided for control of the afterloader.

As aforementioned, operation of the system as a whole is controlled by one or more computing resources which are in one embodiment configured to implement the method illustrated schematically in Fig. 6.

Referring now to Fig. 6, once the procedure is commenced, the dose database and alert criteria are loaded, the computing system controlling the afterloader is provided with the source start position, and the afterloader is controlled to move the source to the predetermined source start position. In the preferred arrangement the afterloader is configured to move the source relatively quickly to the first dwell position (and between subsequent dwell positions) so that only the tissue to be treated at specified dwell positions is subjected to a significant dose.

Irradiation of tissue occurs at all times once the source has been advanced into the patient, but once the source is determined to be in a given dwell position, a timer is started. Radiation emitted by the source is then detected in real time and both the charge for that position and the integrated dose for that stage of the procedure are incremented.

The detected dose for that dwell position and, optionally, the integrated dose are compared in real time with the planned dose for that position and the planned integrated dose. If either the detected dose for that position or the integrated dose should exceed the corresponding planned dose or integrated dose (determined in accordance with the alert criteria), the operator is alerted, the source is withdrawn and the procedure is terminated.

If the measured dose is less than the planned dose, it is determined whether the timer has reached the dwell time for that stage of the procedure. If the timer is less than the planned dwell time, detection of radiation is allowed to continue. If the timer is equal to the planned dwell time, the timer is reset and it is determined whether the treatment plan contains any further dwell positions. If the treatment plan does contain further dwell positions, the next source position is loaded and the procedure repeated. If the final dwell position has been reached, the source is withdrawn and the procedure is terminated.

As aforementioned, the measured and planned doses are stored in the reporting system, and the output of this system may be formatted for use with other treatment planning and patient management software.

Referring now to Figs. 7 and 8 of the accompanying drawings, there is shown an intracavitary probe 80 according to another embodiment of the present invention. Fig. 8 is a longitudinal cross-sectional view of the probe along the line A— A in Fig. 7, and Fig. 7 is a view of the probe from the proximal end thereof (i.e. a view from the end that is not inserted into the patient). The same reference numeral is used hereafter where the features of the probe shown in Figs. 7 and 8 are the same as or similar to features of the probe shown in Fig. 2.

As with the probe of Fig. 2, the probe 80 of this embodiment comprises a sterile cylinder 21 that is coupled at one end to a collar 17 and is passed through a support block that abuts against the patient when the probe is inserted into the patient's body cavity (for example the rectum).

The collar (as before) comprises a plurality (in this instance eight) apertures 82 through one or more of which a catheter (not shown) is inserted in use. The apertures are numbered, as shown, to make it easier for an operator to discriminate between catheters. As shown in Fig. 7, the apertures 82 are arranged to register with catheter bores 84 formed within the sterile cylinder so that sources and/or detectors may be moved into and out of the probe.

The collar of this embodiment further comprises with a larger aperture 86 (in this instance a central aperture) that has a radius which is significantly larger than that of the apertures 82 through which catheters may be inserted. The larger aperture 86 registers with a larger bore 88 formed in the sterile cylinder.

The larger aperture and bore 86, 88 are provided to enable the probe to be connected to an insertion aid (such as a relatively rigid applicator) which can be used to insert the probe into the patient's body cavity. Once the probe has been inserted the insertion aid can be removed, and the larger bore 88 can then be used to accommodate a detector array of the aforementioned type (namely a catheter with a plurality of detectors of the type depicted in Fig. 4 housed within it). Whilst skilled persons will appreciate that any number of detectors may be included in the array, in an envisaged arrangement ten detectors are provided.

Referring now to Fig. 9, the detector array 90 may additionally be employed to screen a part of the patient that does not need to be irradiated. For example, as shown in Fig. 9, if a particular treatment regimen required a source 92 to be advanced into and drawn out of a catheter located in catheter aperture 7, then it may be advantageous to shield patient tissue diametrically opposite the source 92 (i.e. to the right hand side of the probe as indicated in Fig. 9) from radiation. This could readily be accomplished by coating the periphery of a portion of the detector array 90, for example a portion of the sheath, with an appropriate radiation attenuating material 94.

Fig. 10 is a schematic representation, in cross-section, of the proximal region of an intracavitary brachytherapy probe 96 according to another embodiment of the present invention. In this embodiment the probe comprises an additional outer sheath 98 into which the sterile cylinder is inserted. The sheath 98 is selectively expandable, and is shown in Fig. 10 in its expanded state. Expansion of the sleeve may be accomplished by filling it with a fluid (preferably a biocompatible or inert fluid), once the probe is inserted into the patient, so as to introduce a space between the periphery of the probe and patient tissue immediately adjacent thereto. The provision of a space between the probe and the patient, as well as affecting the degree to which the patient is irradiated, also provides a gap into which one or more detectors, for example detectors of the type described above in connection with Fig. 5, may be inserted (in the preferred embodiment by passing them through catheters inserted in the gap).

Fig. 1 1 is a schematic representation, again in cross-section, of the proximal region of an intracavitary brachytherapy probe according to yet another embodiment of the present invention. In this embodiment the probe 100 also comprises an expandable outer sheath 102 (which sheath is shown fully expanded in Fig. 1 1 ), but in this instance the sheath is configured to have an outer layer 104 and an inner layer 106 that together define a space which is subdivided into smaller chambers 108 and larger chambers 1 10 by a plurality of baffles 1 12.

In an envisaged implementation, the smaller chambers 108 are each independently expandable and are each configured to receive a catheter (not shown), into which a detector of the type depicted in Fig. 5 may be advanced. The catheter chambers may be, as shown, generally aligned with the catheter bores in the sterile cylinder 21 , or in an alternative arrangement the catheter chambers may be radially offset from the catheter bores.

In the preferred embodiment, the larger chambers 1 10 are also independently expandable so that neighbouring chambers can be expanded to differing degrees, thereby differentially varying the distance between the probe and the patient (i.e. so that the space between the probe and jacket is asymmetrical about the periphery of the probe). In a particularly preferred arrangement the larger chambers, and optionally also the smaller chambers, are configured to be capable of receiving a radiation attenuating liquid - which liquid may be used to shield a region of the patient from irradiation.

Fig. 12 is a schematic illustration of the abovementioned treatment regimen (where a source 92 is advanced into and drawn out of a catheter located in catheter aperture 7), but in this embodiment instead of shielding patient tissue diametrically opposite the source 92 by coating the periphery of a portion of the detector array 90, the expandable chambers (identified with reference numeral 1 14) nearest the tissue to be shielded have been filled with an appropriate radiation attenuating fluid.

As will immediately be appreciated by persons of ordinary skill in the art, the probes depicted in Figs. 7 to 13 are eminently suitable for use with the apparatus depicted in Fig 3, for example in accordance with the method depicted in Fig. 6.

It will also be appreciated from the foregoing that the teachings provided herein provide a detector that can be read using any conventional electrometer to provide total integrated absorbed dose, and that the system can provide integrated and time-resolved absorbed dose, and a direct measure of the absorbed dose close to the tumour site and hence a report of the difference between planned dose and delivered dose. By providing that the detector fits within existing catheters the system can readily and quickly be employed to provide in vivo dosimetry for HDR brachytherapy.

It will also be appreciated that whilst certain presently preferred embodiments of the present invention have been set out above, the scope of the present invention is not limited to those embodiments. Rather, the scope of the present invention extends to any combination of features herein described irrespective of whether that particular combination of features has been explicitly enumerated in the accompanying claims.

For example, whilst it is envisaged to provide two radiation sensors for each detector, a greater number of sensors could instead be provided. In addition, or alternatively, one of the sensors could be swapped for a different type of sensor, for example a temperature sensor. It is also envisaged to provide patient specific detectors that include a processor for storing data.

Skilled persons will also recognise that modifications may be made to the embodiments described above without departing from the spirit and scope of the present invention. For example, it will immediately be apparent to skilled persons that functionality described herein may be implemented in hardware, software or by means of a combination of hardware and software. It will also be apparent that whilst an electrometer is preferred, any of a variety of different devices known to persons skilled in the art may instead be employed to measure the radiation emitted.

Claims

1 . An in-vivo dose detector for an HDR brachytherapy system, the detector comprising first and second sensors that are operable to detect radiation from a source used to irradiate a tissue to be treated in the course of an HDR brachytherapy treatment, wherein said sensors are arranged in said detector so as to be differently orientated from one another.

2. A detector according to Claim 1 , wherein said first and second sensors each comprise a semiconductor diode configured to operate in a photovoltaic mode without an applied voltage bias, or with an applied bias.

3. A detector according to Claim 1 , wherein said first and second sensors each comprise a MOSFET, preferably a MOSFET specifically designed to be responsive to radiation.

4. A detector according to any preceding claim, wherein the detector comprises a catheter, said sensors being provided within said catheter.

5. A detector according to Claim 4, wherein the sensors are sealed within the catheter.

6. A detector according to Claim 5, wherein the sensors are sealed within the catheter by a sealant that prevents light from being detected by the sensors.

7. A detector according to any of Claims 4 to 6, wherein the catheter includes one or more locating rings that enable the position of the detector to be accurately determined.

8. A detector according to Claim 7, wherein the locating rings are of titanium or nickel.

9. A detector according to any preceding claim, further comprising a substrate to which said sensors are attached.

10. A detector according to Claim 9, wherein the substrate is flexible.

1 1 A detector according to any preceding claim, comprising one or more additional sensors, wherein each of said first, said second and said one or more additional sensors are differently orientated with respect to one another.

12. An in-vivo dose detector array for use in an HDR brachytherapy system, the array comprising a plurality of detectors according to any preceding claim provided in a single catheter.

13. An intracavitary probe for an HDR brachytherapy system, the probe comprising: a holder having a plurality of smaller bores into each of which a catheter may be inserted and a further larger bore into which a detector array according to Claim 12 or a detector according to any of Claims 1 to 1 1 may be inserted, the probe being configured to hold said catheters and said detector/array in a predetermined positional relationship to one another.

14. A probe according to Claim 13, wherein said smaller bores are all generally equidistant from said larger bore.

15. A probe according to Claim 14, wherein said smaller bores are equally angularly located about said larger bore.

16. A probe according to any of Claims 13 to 15, further comprising a jacket into which the holder is inserted, the jacket being expandable to provide a space between the jacket and a peripheral surface of the holder.

17. A probe according to Claim 16, wherein the jacket is expandable to enable a detector according to any of Claims 1 to 1 1 to be inserted into said space.

18. A probe according to Claim 16, wherein said jacket is configured to provide a plurality of independently expandable chambers.

19. A probe according to Claim 18, wherein said jacket is non-uniformally expandable by expanding only some of said chambers and/or by expanding one or more of chambers by less than their fullest extent.

20. A probe according to Claim 18 or 19, wherein one or more of said chambers is configured to be expandable by injecting a liquid into said one or more chambers, said liquid preferably comprising a radiation attenuating liquid.

21 . An HDR brachytherapy system comprising:

a first catheter insertable into a tissue to be treated, and through which a radioactive source can be moved by an afterloader to irradiate the tissue at one or more dwell positions set out in a treatment plan;

an in vivo dose detector according to any of Claims 1 to 1 1 movable to a detection position within said tissue to be treated; and

means for measuring radiation detected by the detector when the detector is in said detection position and said source is in said one or more dwell positions.

22. An HDR brachytherapy system comprising:

an intracavitary probe according to any of Claims 13 to 20;

a catheter inserted into one of said smaller bores, and through which a radioactive source can be moved by an afterloader to irradiate tissue at one or more dwell positions set out in a treatment plan;

a detector according to any of Claims 1 to 1 1 or a detector array according to Claim 12 provided in said larger bore; and

means for measuring radiation detected by the detector/array when the source is in said one or more dwell positions.

23. A system according to Claim 21 or 22, comprising means for determining from said treatment plan a planned dose for each said dwell position.

24. A system according to Claim 23, wherein said determining means is operable to determine from said treatment plan an integrated planned dose for all positions to which said source has been moved.

25. A system according to Claim 23, comprising a comparator operable to compare a measured radiation dose to a planned radiation dose for a given dwell position, and to output a signal indicative of said comparison.

26. A system according to Claim 24, wherein said determining means is operable to determine an integrated measured dose for all positions to which said source has been moved, the system comprising a comparator operable to compare an integrated measured dose to an integrated planned dose, and to output a signal indicative of said comparison.

27. A system according to Claim 25 or 26, comprising a reporting system for receiving and storing said signal output by said comparator.

28. A system according to Claim 27, wherein said reporting system is configured to receive patient alert criteria and activate an emergency procedure in the event that the signal output by the comparator should conflict with said patient alert criteria.