AU2011202384A1 - Miniature dosimeter systems devices and methods for detecting radiation exposure levels - Google Patents

Abstract

In one aspect of this invention, there is provided, a miniature dosimeter system comprising: (a) a holder for a storage phosphor, (b) a detector for detecting photoluminescence from the storage phosphor, (c) a light source which is operatively coupled to the storage phosphor holder for producing an excitation wavelength to the storage phosphor, (d) one or more optical elements which are arranged in a manner which: (i) substantially minimizes fluorescence from the storage phosphor and optical elements reaching the detector; (ii) substantially maximizes collection and detection of the luminescent wavelength from the storage phosphor; and (iii) substantially minimizes the excitation wavelength reaching the detector; wherein at least one of the optical elements is a first wavelength selective filter for directing a first excitation wavelength from the light source to the storage phosphor and another optical element is a second wavelength selective filter for directing a second luminescent wavelength from the storage phosphor to the detector. There is also provided devices and methods using the miniature dosimetry system according to this invention. 4-- ------ -------- ' (36) SPECULAR REFLECTION

Description

AUSTRALIA Regulation 3.2 Patents Act 1990 Complete Specification Standard Patent APPLICANT: NewSouth Innovations Pty Limited, Dosimetry & Imaging Pty Ltd Invention Title: MINIATURE DOSIMETER SYSTEMS DEVICES AND METHODS FOR DETECTING RADIATION EXPOSURE LEVELS The following statement is a full description of this invention, including the best method of performing it known to me: MINIATURE DOSIMETER SYSTEMS, DEVICES AND METHODS FOR DETECTING RADIATION EXPOSURE LEVELS Field of the Invention The present invention relates to a miniature dosimeter system, a method for the detection and monitoring of radiation exposure using the miniature dosimeter system and devices comprising the miniature dosimeter system. In particular, the invention relates to miniature dosimeter systems, methods, and devices for the detection and monitoring of ionising radiation, such as X-ray, y-ray and UV radiation, by means of photo luminescent storage phosphors. Suitable applications for the miniature dosimeter system, devices and methods of the present invention include detection of radiation in military, homeland security, emergency response, background radiation surveys, personal radiation monitoring in general, and applications in the diagnostic and therapeutic medical fields which involve radiation delivery. Background Optically stimulated storage phosphor materials, which form metastable electron-hole pairs upon exposure to ionising radiation such as X-rays, y-rays and UV radiation are well documented. Such compounds have found use in imaging plates for medical imaging, which operate by exposing the imaging plate to the radiation to be detected and a subsequent readout step where the plate is exposed to long wavelength visible or near-infrared laser light (e.g. red light) to cause the latent X-ray energy within the phosphor to be released as emission of short wavelength visible light (e.g. blue-green light). This imaging method is called computed radiography, and the visible light emission from the phosphor is then detected and a resultant electric signal converted into a digital format for recording and display on a display screen. It should be understood that a problem when using these conventional optically stimulated phosphors is that the readout step erases the information stored in the phosphor. The application for storage phosphors in dosimetry typically include a dosimetry card or dosimetry badge incorporating a thermoluminescent or optically stimulated phosphor for recording the radiation dosage exposure. With both thermoluminescent and optically stimulated phosphors, the information regarding the radiation dosage exposure is deleted when the dosimetery card or badge is read. Thus, a dosimetry card or badge does not retain cumulative radiation exposure data after the card or badge is read. 1 WO 2006/063409 (H. Riesen et a[) discloses a different class of photoluminescent (photoexcitable) storage phosphors based on a rare earth element in a trivalent +3 oxidation state, which reduces to the divalent +2 oxidation state upon exposure to X-ray, y-ray or UV radiation. A preferred example of such a phosphor is nanocrystalline BaFCl: Sm3*, which forms a relatively stable Sm2+ metal ion electron trap upon exposure to X-ray, y-ray or UV radiation. These photoluminescent (photoexcitable) storage phosphors disclosed in WO 2006/063409 differ from the conventional optically stimulated phosphors in that photoexcitation of the phosphor does not cause annihilation of an electron-hole pair but instead causes photoluminescence of the induced optical centres characterized by very narrow emission lines without automatic erasure of the information in the phosphor. Photoexcitation of the photoluminescent phosphor by short wavelength light (e.g. blue light) will cause a relatively long wavelength emission (e.g. red wavelength emission), and the stored X-ray energy within the phosphor is not released. WO 2006/063409 teaches that these stable divalent rare earth (RE2+) centres formed upon exposure to radiation provide much narrower luminescence lines and significantly improved contrast ratios than conventional phosphors, and hence result in improved sensitivity and facilitate the use of reduced radiation dosages for medical imaging. Furthermore, when the photoluminescent (photoexcitable) storage phosphor is used in an imaging plate, the stored information in the imaging plate is not deleted automatically upon reading of the radiation storage information, but may be erased deliberately by exposure to light of an appropriate wavelength and intensity, to allow re-use of the imaging plate in detection of radiation. WO 2009/052568 (H. Riesen et al) describes an apparatus and method for detecting and monitoring radiation. The apparatus is suitable for reading photoluminescent (photoexcitable) storage phosphors of the type described in WO 2006/063409, including at least one gating element for gating the excitation light source from the phosphorescent emission from the phosphor. The contents of WO 2006/063409 and WO 2009/052568 are both incorporated herein by reference. There exists a need to provide a convenient, portable, accurate and compact radiation monitoring device and a method which can be used for personal radiation monitoring applications and which can achieve multiple or continuous radiation dosage measurements, including real time measurement of radiation exposure on a person. This may be envisaged 2 to be critical for radiation measurement applications in situations where an emergency response is required such as for workers on nuclear energy plants, or for the general public inhabiting areas near nuclear plants, where there has been radiation leaks, military personnel in a hostile environment where radioactive materials may be present and other emergencies where it is critical to read multiple or continuous radiation dosages or measurement to indicate personal radiation exposure levels for workers, emergency response staff and the general public around the location of the emergency. Accordingly, the present invention seeks to address this need or provide an alternative to the prior art. SUMMARY OF THE INVENTION In one embodiment, the present invention aims to provide a miniature dosimeter systems, devices and methods for detection and monitoring of radiation exposure, with uses for example in the fields of security, emergency response and medicine such as radiation therapy and medical diagnostics, and in general, personal radiation monitoring for the public. Uses for example for the miniature dosimeter system, devices and methods include detection of radiation in military, homeland security, emergency response and diagnostic and therapeutic medical fields involving radiation delivery. In one embodiment of the present invention, there is provided a miniature dosimeter system comprising: (a) a holder for a storage phosphor, (b) a detector for detecting photoluminescence from the storage phosphor, (c) a light source which is operatively coupled to the storage phosphor holder for producing an excitation wavelength to the storage phosphor, (d) one or more optical elements located which are arranged in a manner which: (i) substantially minimizes fluorescence from the storage phosphor and optical elements reaching the detector; (ii) substantially maximizes collection and detection of the luminescent wavelength from the storage phosphor; and (iii) substantially minimizes the excitation wavelength from the light source reaching the detector; wherein at least one of the optical elements is a first wavelength selective filter for transmitting a first excitation wavelength from the light source to the storage phosphor and at 3 least another optical element is a second wavelength selective filter for transmitting a second luminescent wavelength from the storage phosphor to the detector. In the miniature dosimeter system, the optical elements are arranged so as to extract an extremely low red light signal in comparison to the blue excitation light. The preferred embodiment of this system allows the measurement of red light levels that are lower by a factor of 10-16 compared to the blue excitation light. In a particular embodiment of the miniature dosimeter system of this invention, excitation light is directed at an angle of incidence (0) onto the phosphor located on a holder. The light is preferably blue light wavelengths which are directed onto the phosphor located on the holder at an angle of incidence (0). The angle of incidence (0) may be set at a suitable angle such that specular reflection of the blue light wavelengths from the phosphor located on the holder will miss a further optical element which is preferably a dichroic mirror. The angle of incidence (0) may be in the range of from 50 to 350, more preferably 100 to 250 or 10' to 15*. In a further embodiment, the miniature dosimeter system comprises a cascading filter arrangement. In a further embodiment of the present invention, there is provided a method of detecting radiation on or around a subject comprising the step of measuring radiation on the subject by way of the miniature dosimeter system of the first embodiment of the present invention. In a yet further embodiment of the present invention, there is provided a device comprising the miniature dosimeter system of the present invention. The device may be a miniature reader, a dosimeter badge, a radiation detection probe or a substantially rectangular shaped device. In one example, the substantially rectangular shaped device is in the shape of a card. Further embodiments of the miniature dosimeter system, device and methods of the present invention will be apparent from the detailed description below, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS The description is made with reference to the accompanying drawings; of which: Fig. 1 is a schematic representation of a miniature dosimeter system in accordance with a first embodiment of this invention; 4 Fig. 2 is a schematic representation of a miniature dosimeter system in accordance with a second embodiment of this invention; Fig 2a is a representation of a first timing pattern of the optical switch used in the second embodiment of this invention; Fig.3 is a schematic representation of a miniature dosimeter system in accordance with a third embodiment of the invention; Fig 3a is a representation of a second timing pattern of the LCD shutters used in the third embodiment of this invention; Fig. 4 is a schematic representation of a miniature dosimeter system in accordance with a fourth embodiment of the invention; Fig 4a is a representation of a third timing pattern of the different mirror positions used in the fourth embodiment of this invention; Fig. 5 is a schematic representation of a miniature dosimeter system in accordance with a fifth embodiment of the invention; Fig 5a is a representation of a fourth timing pattern of the different mirror positions used in the fifth embodiment of this invention; Fig. 6 is a schematic representation of a miniature dosimeter system in accordance with a sixth embodiment of this invention; Fig. 6a is a schematic representation of an alternate optical element which may be used in the sixth embodiment of this invention; Fig. 7 illustrates an embodiment of a portable, compact dosimeter system with integrated dosimeter reader and phosphor holder in accordance which is a generally rectangular shaped device in accordance with this invention; Fig. 8 illustrates an embodiment of the invention comprising a dosimetry reader unit and probe adapted for medical use in accordance with this invention; Fig 9 illustrates a plan view of two parts of a dosimeter badge which comprises a miniature dosimeter system in accordance with this invention; and Fig. 10 illustrates a schematic representation of a device comprising a miniature dosimeter system of the first embodiment of this invention and which may utilise the dosimeter badge of Fig.9. DESCRIPTION OF THE PREFERRED EMBODIMENTS In Figure 1, there is shown a miniature dosimeter system in accordance with a first embodiment of this invention which comprises: a light source (10), a filter (11), a first 5 dichroic mirror (12), a second dichroic mirror (14), a collimation lens (16), a notch filter (18), a first longpass interference filter (20), a second longpass interference filter (22), a third longpass interference filter (24), a first bandpass interference filter (26), a second bandpass interference filter (28), a lens (30), a reflecting element (32), a silicon photodiode (34) and a phosphor holder (36) which holds a storage phosphor. The storage phosphor in this example is a BaFCI/Sm storage phosphor, the preparation of which is disclosed in the examples taught in WO 2006/063409 (H Riesen et al). It should be noted that the BaFCI/Sm phosphor contains Sm 3 + ions which are reduced to Sm 2 + ions upon exposure to ionising radiation. As seen in Figure 1, the miniature dosimeter system includes a light source (10) which in one particular embodiment is a blue-violet or blue laser diode. The light of the blue violet or blue laser diode (10) may be for example a 405nm, a 415nm, a 420nm or 440nm laser diode or any other suitable diode. In use, the light source (10), specifically a blue or blue-violet laser diode emits blue or blue-violet light that is filtered by a filter (11) which in one particular embodiment is either a first short pass filter (450nm) or a blue bandpass filter (400nm to 450nm). The filter (11) seeks to substantially attenuate light with wavelengths longer than the nominal laser wavelength that are emitted by the laser generated for example by the semiconductor junction glow which is then directed onto the first dichroic mirror (12). The first dichroic mirror (12) selectively reflects the blue light wavelengths onto the phosphor located within the phosphor holder (36). The first dichroic mirror (12) also minimises any red light emitted by the blue or blue-violet laser diode. Whilst the first dichroic mirror (12) reflects blue light wavelengths onto the phosphor located on the holder (36), the first dichroic mirror (12) also passes red light wavelengths through the mirror (12) without reflection such that the red light is transmitted along an axis marked as A which extends along an axis from the light source (10) to the first dichroic mirror (12) which is best shown in Figure 1. The use of the first short pass or bandpass filter (11) and the dichroic mirror (12) in the dosimeter reader substantially minimises the transmission of red light wavelengths onto the phosphor located in the holder (36) and to other optical elements including the second dichroic mirror (14). This is important since any transmission of red light wavelengths from the light source (10) to the phosphor located in the phosphor holder (36) and to the second dichroic mirror (14) will reduce the sensitivity of the dosimeter system. Once the phosphor is exposed to the blue light wavelengths reflected from the first dichroic mirror (12), the BaFCl/Sm phosphor will emit red light wavelengths which occur via a f-f luminescence, e.g. 5 Dr- 7 Fj transitions, of Sm 2 " via the intense f-d excitation in the blue 6 region of the spectrum. The red light luminescent wavelengths are then reflected by the second dichroic mirror (14) to the collimation lens (16). The second dichroic mirror (14) also transmits any emitted or reflected blue light wavelengths along axis marked as B to increase the sensitivity of the dosimeter system. A feature of this particular embodiment of the miniature dosimeter system is that the angle of incidence (0) as shown in Fig 1 of the blue light wavelengths onto the phosphor located on the holder (36) may be set at a suitable angle such that specular reflection of the blue light from the phosphor located on the holder (36) will miss the second dichroic mirror (14). In a preferred embodiment, the specular reflection of the blue light will miss the second dichroic mirror (14) by preferably a substantial margin. As shown in Figure 1, the angle of incidence (0) is equal to the angle of the specular reflection In the embodiments depicted in Figs 1, 3, 4 and 5 the angle D is preferably maximally different to the angle of the red light path (A) as shown in Fig 1. The angle A of the holder 36 in relation to the axis of the emitted red light from the holder 36 to second dichroic mirror (14) is 90 + phi degrees. When A (delta) = (90 -2. phi) degrees, D (phi) is in the range between 50 to 350 and preferably in the range of 100 to 250, still preferably 100 to 150. Accordingly, the angle A is 800 to 200 when (D is 50 to 35'. The collimation lens (16) then collimates the red light luminescence wavelengths emitted from the storage phosphor on the holder (36) before the red light wavelengths are subjected to a cascading filter arrangement. The cascading filter arrangement may comprise in a particular embodiment, the notch filter (18), the first long pass interference filter (20), the second longpass interference filter (22), the third longpass interference filter (24), the first bandpass interference filter (26), the second bandpass interference filter (28) and lens (30) aligned along a first longitudinal axial direction from the second mirror (14) to the lens (30). The alignment of the lens (30) with the other optical elements, notch filter (18), first long pass interference filter (20), second long pass interference filter (22), third longpass interference filter (24), the first bandpass interference filter (26), and the second bandpass interference filter (28) seeks to minimise any autofluorescence from the optical elements in the dosimeter system together with any red background emission from the light source and fluorescence from the phosphor and any blue light from the laser (10) reaching the detector (34). 7 In this particular cascading filter arrangement shown in Figure 1, the emitted red light is filtered by the notch filter (18) which filters the laser light with an optical density of greater than 4 and preferably with an optical density of high OD e.g. 5 to 10 or higher. The emitted red light then needs to pass through the first long pass interference filter (20). The filter (20) may transmit light of wavelengths greater than about 450nm or 500nm. If the light source (10) emits wavelengths of 405nm then the filter should only transmit wavelengths greater than about 450nm. However, if the light source (10) emits wavelengths of 440-470 nm then the filter will transmit wavelengths greater than about 500nm and with an optical density of greater than 4. After the red light passes through the first long pass interference filter (20), the red light then passes through a second long pass interference filter (22) which transmits light with wavelengths of greater than 650 nm or 680nm and a third long pass interference filter (24) which transmits light with wavelengths of greater than 680 nm or 71Onm, both of which occur at an optical density of greater than 4. The red light is then further passed through the first and second bandpass interference filters (26) and (28), respectively, which transmit wavelengths of between 680 to 690 nm or 720 to 730nm, 686 and 688 nm or 726 to 729 nm and which block light of wavelengths outside of these narrow ranges. The skilled person would appreciate that the cascading filter arrangement can be modified such that the filters (18), (20), (22), (24), (26), and (28) transmit suitable wavelengths so that other f-f lines at 687nm, 728nm, 750nm and 815nm and other suitable wavelengths can also be monitored by the miniature dosimeter system of this invention. The transmitted red light then is refocussed by the lens (30) and further directed by a light reflecting element (32) to bend the light from the axial direction of lens (16), filters (18), (20), (22), (24) and (26), (28) to a silicon photodiode detector (34). The light reflecting element (32) may be either a prism as shown in Figure 1 or in an alternative embodiment a third dichroic mirror which reflects red light but transmits blue light along the axial direction of the lens (16), filters (18), (20), (22), (24), (26) and (28). It is noted that the red light of the Sm 2 ion may be detected by the silicon photodiode detector (34) preferably in combination with an amplifier element (not shown). In one example, the amplifier element may be an ultra low noise transimpedance amplifier preferably with a gain of 1012 volts/watt (v/w). In Figure 2, there is provided a second embodiment of this invention. The dosimeter system includes a light source (40), a first short pass (or bandpass) filter (42), a first optic fibre (44), a MEMS optical switch (46), a second optic fibre (48), a collimator (50), a holder 8 (52) which preferably holds the BaFCI: Sm storage phosphor, a third optic fibre (54), a first filter (56), a second filter (58) and a detector (60). The light source (40) may be a blue-violet or blue laser diode as in the first embodiment described above. However, in this embodiment of the invention, a MEMS optical switch is connected to the light source (40) by an optic fibre (44) which transmits light wavelengths in the range of from 400 to 500nm. Preferably, there is a collimating lens or filter (42) located between the light source (40) and the MEMS optical switch (46). The MEMS optical switch (46) is a bidirectional optical switch which in a first position allows blue light to pass from the optic fibre (44) to a second fibre (48) that is directed towards the storage phosphor located on the holder (52). The light output of the second fibre (48) is preferably collimated by a collimation lens (50) located in front of the phosphor holder (52). In the second position of the MEMS optical switch (46), the switch will allow the emitted red light to pass from the phosphor holder (52) via the lens (50) and second optic fibre (48) to the third optic fibre (54). The red light emission then passes through the filters (56) and (58) to a silicon detector (60). The optical switch is preferably set with a timing pattern as shown in Figure 2a. In Figure 2a, it can be seen that the direction of travel of light will move to accord with the pattern as depicted where A represents travel of light in a first direction whilst B represents travel of light in the second opposite direction. The depiction of the direction of travel of the light is also shown against time in milliseconds along the x- axis. In Figure 3, there is shown another embodiment of the present invention. The dosimeter system comprises a light source (62), a first short pass (or bandpass) filter (64),a first collimation lens (66), a second collimation lens (72), a first LCD (liquid crystal device) shutter (68), a second LCD shutter (74), a phosphor holder (70), a longpass filter (76), a bandpass filter (78), a second collimation lens (80) and a detector (82) In Figure 3a, there is shown a further timing diagram for the first LCD shutter (68) and the second LCD shutter (74) for the embodiment as depicted in Figure 3. The key aspect of the timing for the first and second LCD shutters (68) and (74) is that only one of the shutters, either the first shutter (68) or the second shutter (74) is open at the same time. In other words, when the LCD shutter (68) is in an open (or transmission) mode (or position), then the LCD shutter (74) is in the closed (or blocked, or non-transmission) mode (or position). Similarly, when the LCD shutter (68) is in a closed position (or blocked or non 9 transmission) mode or position, the LCD shutter (74) is in the open (or transmission) mode (or position). In addition the timing of LCD shutters (68) and (74) may also include a period of time where both LCD shutters (68) and (74) are closed so as to avoid any possibility of having a common light path. The time period where both LCD shutters (68) and (74) are closed may be optimised based on the characteristics of the LCD shutters. For example, this time period may be the time delay from the activation signal to the time that the shutter transitions from the transmission mode to the non-transmission mode. In this embodiment, the LCD shutters (68) and (74) shown in Fig 3 may be replaced by electro-mechanical shutters, for example of the type used in photographic cameras. In this embodiment the LCD shutters shown in Fig 3 may be replaced by a mechanically activated plate (not shown) with an aperture that is moved alternately so that the aperture allows the blue light to pass from the light source (62) to the phosphor holder (70) and then moves to allow the red light to pass from the phosphor holder (70) to the detector (82). The mechanically activated plate may have one aperture and either oscillate from side-to-side or the aperture may be located on the radius of a disk which is rotated. In the case of a rotating disk, there may be multiple apertures to allow for more than one blue excitation/red detection cycle per rotation of the disk. The multiple apertures are arranged so that there is never an optical path from the blue light source (62) to the holder (70) and from the holder (70) to the detector (82) at the same time. In this embodiment the LCD shutters may be replaced by two optical tuning fork choppers (not shown) that are synchronized so that the aperture of the excitation and emission light are closed and open out of phase by 180 degrees. The optical tuning forks may have a pair of legs which have a vane on each respective leg. Alternatively, in a further embodiment, just one tuning fork may be used where the two respective vanes are made of an opaque material that cover the excitation and emission light apertures and are arranged so that the open-close time is out of phase by 180 degrees. In Figure 4, there is shown a further embodiment of a dosimeter system where the light source (90), a short pass (or bandpass) filter (92) and lens (93) act to collimate the blue light onto one or more movable electronic mirrors (94) and (98) each of which is capable of two positions, (A) and (B). In one position, the blue light is directed by mirror (94) onto the phosphor shown in holder (96) to cause a red light emission as previously described above. Once the red light emission is occurring, the mirror (94) may be positioned in a further 10 position to exclude blue light from reaching the phosphor located on the holder (96) and the mirror (98) is positioned to allow the red light emission to be focussed onto the detector (100). The mirror (98) may also be moved to a position where no light is reflected onto the detector (100) In Figure 4a, there is shown a timing diagram similar to Figure 3a for the different mirror positions A and B which are shown for mirrors (94) and (98), respectively. These timing patterns shown in Figure 4a are optimum timing patterns to increase sensitivity of the miniature dosimeter system. In Figure 5, there is shown a yet further embodiment of the miniature dosimeter system of the present invention which further depicts a light source (110), a short pass (or bandpass) filter (112) and lens (114) which combine to focus the blue light onto the phosphor located in a holder (118) which causes as described above a red light emission from the storage phosphor. The lens (120) collimates the red light from the phosphor onto the mirror (122). Preferably, the electronic mirrors (116), (122), (124) and (126) act in synchrony to: 1) direct blue light to the phosphor holder (118) and 2) when the phosphor is luminescing with red light, exclude blue light from the phosphor holder and direct the red light to the detector (128). In Figure 5a, there is shown a timing diagram similar to Figures 3a and 4a for the different mirror positions which are shown for mirrors (116), (122), (124) and (126), respectively. The time intervals for each mirror drive is optimised to: a. maximize the collection and detection of the luminescent wavelength (red light) from the dosimeter phosphor b. minimize the excitation wavelength (blue light) reaching the detector. The leading and trailing edges of the drive signals to the mirrors (116), (122), (124) and (126) may each be individually adjusted to achieve the optimisation noted above, taking into account the characteristics of the electronic mirrors, for example the time delay from the activation signal to the time that the mirrors moves and is in the desired position. In one example of this embodiment, the time periods TI, T2 and T3 are all equal to 0.1 milliseconds. In a second example the time period TI is equal to 0.1 milliseconds and T2 and T3 are both equal to zero. In Figure 6, there is shown a yet further embodiment of the dosimeter system of the present invention which further depicts a light source (130), a short pass (or bandpass) filter (132) and lens (134) which combine to collimate the blue light on a triangular prism (136) coated with a storage phosphor (138) on one face. 11 The triangular prism (136) comprises faces (140), (142) and (144) which is shown in cross sectional view. The prism (136) is composed of a transparent material that has the correct optical properties to achieve total internal reflection (high refractive index) of the blue excitation light. In this embodiment, the blue light enters the prism via face (140) and is totally internally reflected at an interior surface of opposite face (142) and exits through face (144) of the prism (136) as shown in Figure 6. The exterior of face (142) of the prism (136) is coated with the storage phosphor (138) as shown in dotted outline on the exterior surface of face (142). As described above, the blue light excites the storage phosphor via the evanescent wave and causes the storage phosphor to emit red light wavelengths which are transmitted outside of the prism (136) towards a detector (154) which is effectively isolated away from the well defined blue light path as shown in dotted outline exiting through face (144) in this embodiment. As described above, once the storage phosphor is excited, the emitted red light will be collimated by a lens (150), filtered by the bandpass filter (152) which in one particular embodiment are from 726nm to 730nm. The red light emission from the storage phosphor passing through the filter (152) is then measured by the detector (154). In a further embodiment shown in Fig 6a, the prism is elongated (160) to allow multiple total internal reflections. This allows the blue light wavelengths to interact with the phosphor (162) located on a face of the elongated prism (160) multiple times and hence this increases the sensitivity of the miniature dosimeter system. The detecting and monitoring componentry of the dosimeter system is preferably of high sensitivity, for example of a resolution of measurement range from IOOnGy to 1OOGy, or optionally from lmGy to 1Gy at a resolution of about 100nGy to ImGy. In use, this measurement represents an incident dose to a surface of a subject such as a person, animal or object. A further embodiment of the dosimetry reader and phosphor holder may relate to a multi-element phosphor holder. Other embodiments of the invention include a self-indicating personal dosimetry device which incorporates the miniature dosimeter system of this invention which indicates the radiation exposure level to which the device has been exposed. A further embodiment of this device is illustrated in Fig. 7, which shows a dosimetry device incorporated into a generally rectangular card shape approximately the height and width of a credit card and about two to three times the thickness. The device may be carried on a person - for example in a wallet. It is envisaged that the device could be used for the general population in an at-risk location or as a backup device for first responder personnel such as Hazmat team members. 12 The device as shown in Figure 7 includes a storage phosphor as previously described, monitoring and measurement apparatus for reading the radiation exposure detected by the phosphor, and a simple electronic display of the exposure level, which may be in the form of green, orange and red LED lights to indicate the danger level. By operation of two of the LEDs at once, the display is able to indicate five exposure levels: green, green and orange, orange, orange and red, and red. The device further includes a power source such as a replaceable or built-in battery. The card shaped device may be formed for example using a printed circuit board (PCB) or surface mounted component circuit board construction, a hybrid of PCB and surface mount construction, or a hybrid substrate including the solid state devices and the storage phosphor. The card may incorporate written material on its surface with instructions as to the appropriate response to each of these levels. Again, this card shaped device is intended for use as a coarse exposure indication rather than a fine measurement, and so requires only a sensitivity of approximately 10 1OOmGy resolution, more preferably 10-50mGy, a less sophisticated readout apparatus such as a pulsed LED for photoexcitation of the phosphor. The various forms of the invention may thus provide a suite of different dosimetry cards and readers based on a common technological platform such that the cards are readable by a number of different devices of varying sensitivity and cost, from self-indicating devices and relatively inexpensive first responder and first-pass screening readers in the event of a mass radiation exposure to more sensitive readers for follow-up triage for allocation of medical treatment. Detection and Monitoring of Radiation Dosage in Medical Therapy A further embodiment of the invention relates to medical applications of dosimetry, and in preferred forms to applications of the invention to dosage detection and regulation in radiation therapy for cancer treatment and the like. One form of cancer treatment used for curative or palliative treatment is radiation therapy, in which ionising radiation beams such as electron beams from a linear accelerator are directed to the specific site of the cancer to destroy the cancerous cells. The beams may be directed from outside the patient's body (external beam radiotherapy) or internally via placement of the radiation source at the tumour site (brachytherapy). In order to reduce side effects and damage to adjacent healthy tissue, the total radiation dosage is usually split into smaller doses delivered over time, both within a single radiation therapy session and over multiple sessions over days or weeks. 13 In radiation therapy, the total radiation dosage, the break-up of that dosage into individual doses and the accuracy of positioning of the radiation beam at the site of the cancer are important to the success of the therapy and in minimising side effects from the therapy. In one embodiment of the invention, an example of which is shown in Fig. 8, there is provided a radiation detection probe for use in detecting radiation applied to a patient in radiation therapy. The probe comprises a radiation detection phosphor element at a portion of the probe, and a probe body having means for guiding the phosphor element to a desired location, for example adjacent to a tumour to be treated. The probe further includes one or more optical transmission elements, for example optical fibres, which allow remote readout of the phosphor by directing a phosphor photoexcitement source such as an LED or laser source of the appropriate wavelength onto the phosphor, and for directing light emitted by the phosphor to a reading device located externally of the patient's body. The phosphor element is located at a remote end of the probe and preferably comprises a phosphor of the type which does not erase upon readout, most preferably a storage phosphor including a trivalent 3+ rare earth element as described above and in WO 2006/063409 and PCT/AU08/001566. A plurality of phosphor elements may be provided in a spaced array, for example over a 1-2cm length of the probe. The phosphor elements may each be provided with a separate optical fibre and readout mechanism, and thus be able to provide information about both the total and distribution of the radiation intensity profile of the treatment beam in the vicinity of the probe, or else may share a common readout and be adapted to provide just a total value for the radiation. The probe body is elongated and flexible, and may include a guidance mechanism for guiding the probe into the desired position, for example a hollow lumen catheter having a guide wire mechanism of the type known per se and well known in respect of surgical probes and remote surgery implements. The probe may be adapted for insertion into the body via a body orifice, e.g. oral, nasal or rectal, or may be adapted for percutaneous insertion and access via the vascular system or direct through the patient's tissue to the site. At the other end of the probe, i.e. the distal end, is an optical connection and optionally other connections for connecting the probe to a detection and readout unit as shown in Fig. 8. 14 The unit incorporates a detection unit for interrogation and readout of the radiation exposure level detected by the phosphor element, incorporating for example the readout technology described above and in WO 2006/063409 and PCT/AU08/001566 except that instead of the blue LED or laser source being directed onto the phosphor card within the device it is directed down the probe via the optical fibre to the phosphor, which becomes photoexcited and emits light as discussed above. As in the embodiment described above and in Fig 2. the second optic fibre (48) may be of a sufficient length (eg I to 5 metres) so it can be placed within or on the patient, and the phosphor material may be bonded (or held in place by and appropriate holder) to the end of optical fibre (48) instead of lens (50) and phosphor holder (52). The optical fibre (48) may be manufactured and supplied to the hospital in sterile form so that it can be used in a patient during a surgical procedure. The length of the optical fibre may allow the readout unit shown in Fig 8 to be positioned outside the surgical sterile field, negating the need to sterilise the readout unit. The light emitted by the phosphor travels back along an optic fibre in the probe to the detector unit, where the emission spectra is detected and analysed to determine the radiation dosage received at the probe location. Separate optical fibres may be used for the photoexcitation source and the phosphor emission back to the unit, or alternatively a single fibre may be shared with use of beam splitter built into the detection unit or interposed between the unit and the probe. In operation, the probe may be positioned in or on the patient prior to commencement of the radiation therapy session so that the phosphor element of the probe is at a desired location, usually directly adjacent the tumour to be irradiated so that the dosage received by the tumour can be determined. Alternatively, the probe can be positioned near healthy tissue adjacent the tumour, to give a reading of what dosage is being received by the healthy tissue. The detected radiation dosage reading may then be used in either detect and display or detect and control modalities for setting dosage for subsequent radiation doses. If detect and display mode is used, the detection unit may be set to display the detected radiation dosage to the clinician and other pertinent information such as a cumulative dosage and a comparison against the scheduled radiation dosage regimen. The unit may also be set to display or sound an alarm signal when the detected dosage is outside certain predefined parameters. The clinician may then adjust the dosages for subsequent doses based on the information displayed and his/her judgement as required. If detect and control mode is used, the detected dosage information from the unit is communicated back to the radiation therapy device for 15 comparison against the pre-programmed dosage regimen and adjustment of the radiation dosages generated by the machine for future doses as required by the clinician. A further embodiment of the device of this invention in the form of a dosimetry badge is illustrated in Fig 9. It has been previously described that the BaFCI:Sm phosphor is significantly more sensitive to lower energy X-Rays as compared to higher energy gamma radiation. In order for the dosimetry system to provide the user with a biologically compensated dose reading, the usual units are sieverts and the typical non hazardous doses are in the range of millisieverts, two or more regions or phosphor are used. One region of the phosphor is exposed to all the radiation from the environment and the other region of phosphor incorporates a filter layer, typically copper or aluminium to limit the phosphor exposure to higher energy gamma radiation by attenuation of the lower energy radiation. In Fig 9, a top or plan view of a dosimeter badge is shown comprising a substrate (180) as shown in the upper part of Figure 9 and a sleeve (190) as shown in the lower part of Figure 9. The substrate (180) comprises a first phosphor region (182) and a second phosphor region (184) which are spaced part from each other. The substrate (180) further comprises on a longitudinal edge region of the substrate (180), a first coloured region (186) and a second coloured region (188) where the colours of regions (186) and (188) are different to distinguish the respective regions from each other. The sleeve (190) as shown in the lower part of Figure 9 also comprises on a longitudinal edge region of the sleeve (190), a first coloured region (192) and a second coloured region (194) where the colours of regions (192) and (194) are different to distinguish the respective portions from each other. The sleeve (190) also comprises a copper filter (196). The copper filter (196) thickness is a parameter that determines which radiation energies are filtered. Typically, in one example the copper sheet is approximately 0.2 mm in thickness. The respective pairs of coloured regions on both the substrate (180) and the sleeve (190) are matched so that a user is guided to remove and insert the substrate (180) into the sleeve (190). In particular, coloured region (186) matches coloured regions (192) and coloured region (188) matches coloured region (194). In order to take a reading from the dosimeter badge, the user removes the substrate (180) from the sleeve (190) and inserts a first half (i.e. a portion of the substrate containing the phosphor (182) and colour region (186) into a reader which in one example is shown in figure 10. 16 After the radiation reading is completed, the user removes the substrate (180) from the reader, rotates the substrate by 180 degrees and inserts the second half of the substrate (ie inserts the portion of the substrate containing the phosphor (184) and coloured region (188) into the reader. The combination of the data from the two readings (ie from phosphor regions 182 and 184, respectively) determine the radiation dose in biological equivalent units, sieverts. Figure 10 shows a device comprising the miniature dosimeter system of the first embodiment and which can be used with the dosimeter badge as shown in Fig.9. In one particular example, the device may have approximate dimensions of from 100mm x 45mm x 45mm or 100mm x 40mm x 15mm. The device comprises a housing (not shown) including the optical components as described in Fig. I except for the storage phosphor holder (36) as shown as component (200) and a second component (202 which comprises control electronics, a power supply management, microcontroller and display driver. There is also provided a LCD display (204), a battery pack or DC power supply (206), control panel buttons and switches (208) and a storage phosphor substrate (180) as shown in Figure 9 or in an alternate embodiment a storage phosphor holder (36) as shown in Figure 1. In operation of the use of the dosimeter badge and device of Figures 9 and 10, a user or object is able to monitor their radiation exposure by use of the dosimeter badge as shown in Figure 9. An example is a person or object being in proximity to a nuclear power station. Alternatively, there may be a soldier in an area where radioactive material may be present. The dosimeter badge as shown is worn or carried on their person in a suitable manner such as for example attaching a badge to clothing or in a pocket. Medical staff or police staff etc carry a portable radiation measuring device such as shown in Figure 10 in a robust, compact housing which contains the components shown in schematic Fig 10 (200, 202, 204, 206 and 208). In order to measure a radiation exposure dose, the dosimeter badge (Fig 9) is dis assembled, ie the substrate (180) is removed from the sleeve (190). The substrate (180) is then inserted into the radiation measuring device and a radiation exposure reading is obtained. The dosimeter badge substrate (180) from the dosimeter badge is also shown in the schematic Fig 10 as item 210. While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and 17 examples are therefore to be considered in all respects as illustrative and not restrictive, and all changes which come within the meaning and range of equivalency are therefore intended to be embraced therein. In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of'. A corresponding meaning is to be attributed to the corresponding words "comprise, comprised and comprises where they appear. It will further be understood that any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates. 18

Claims (26)

1. A miniature dosimeter system comprising: (a) a holder for a storage phosphor, (b) a detector for detecting photoluminescence from the storage phosphor, (c) a light source which is operatively coupled to the storage phosphor holder for producing an excitation wavelength to the storage phosphor, (d) one or more optical elements which are arranged in a manner which: (i) substantially minimizes fluorescence from the storage phosphor and optical elements reaching the detector; (ii) substantially maximizes collection and detection of the luminescent wavelength from the storage phosphor; and (iii) substantially minimizes the excitation wavelength reaching the detector; wherein at least one of the optical elements is a first wavelength selective filter for directing a first excitation wavelength from the light source to the storage phosphor and another optical element is a second wavelength selective filter for directing a second luminescent wavelength from the storage phosphor to the detector.

2. A miniature dosimeter system according to claim 1, wherein the first and second wavelength selective filter is selected from the group consisting of one or more dichroic mirrors, one or more wavelength pass filters, one or more prisms, one or more optical switches, and combinations thereof.

3. A miniature dosimeter system according to claim 1 or 2, wherein the first wavelength selective filter allows blue light wavelengths to be directed from the light source to the storage phosphor.

4. A miniature dosimeter system according to claim 1, 2 or 3, wherein the second wavelength selective filter allows luminescent wavelengths emitted from the storage phosphor to be directed towards the detector.

5. A miniature dosimeter according to claim 4, wherein the luminescent wavelengths emitted from the storage phosphor are red light wavelengths.

6. A miniature dosimeter system according to claim 1 to 5, wherein the first wavelength selective filter is arranged such that the blue light wavelengths are directed from the first wavelength selective filter to the storage phosphor holder at an incident angle such that 19 the corresponding specular reflection of the blue light wavelengths from the storage phosphor holder are directed away from the second wavelength selective filter.

7. A miniature dosimeter system according to claim 6, wherein the second wavelength selective filter is arranged such that luminescent wavelengths emitted from the storage phosphor are directed so that red light wavelengths are directed towards the detector and blue light wavelengths are directed away from the detector

8. A miniature dosimeter system according to claim 6 or 7, wherein the incident angle is an angle of incidence (<D) selected from the group consisting of from 5 to 35 degrees, of from 10 to 25 degrees or of from 10 to 15 degrees.

9. A miniature dosimeter system according to any one of claims I to 8, wherein the first wavelength selective filter and the second wavelength selective filter are dichroic mirrors which are optionally movable.

10. A miniature dosimeter system according to claim 9, wherein the first wavelength selective filter is at least one movable dichroic mirror which is movable from a first position which is co-axial with the direction of travel of the light wavelengths from the light source to the first wavelength selective filter to a second position which is set at an angle of 5 to 45 degrees to the direction of travel of the light wavelengths from the light source to the first wavelength selective filter.

I1. A miniature dosimeter system according to claim 9 or 10, wherein the second wavelength selective filter is at least one movable dichroic mirror which is movable from a first position which is co-axial with the direction of travel of the light wavelengths from the holder to the second wavelength selective filter to a second position which is set at an angle of incidence of 5 to 80 degrees to the direction of travel of the light wavelengths from the holder to the second wavelength selective filter.

12. A miniature dosimeter system according to any one of claims 6 to 11, wherein the dosimeter system further comprises one or more filters which are aligned along an axial direction with the second wavelength selective filter and at least one lens.

13. A miniature dosimeter system according to any one of claims 6 to 12, wherein the one or more filters are arranged in a cascading configuration.

14. A miniature dosimeter system according to claim 13, wherein the cascading configuration of filters includes a series of filters comprising at least a notch filter, a plurality of long pass filters and one or more band pass filters. 20

15. A miniature dosimeter system according to claim 14, wherein the long pass filters transmit light with wavelengths of greater than 500nm, greater than 680nm, and greater than 710nm, respectively.

16. A miniature dosimeter system according to claim 14 or 15, wherein after the plurality of long pass filters, the transmitted red light will pass through one or more band pass intereference filters which transmit light between a wavelength of from 720 to 730nm or from 684 to 688nm, 745 to 755nm or 810 to 820nm.

17. A miniature dosimeter system according to claim 1 or 2, wherein the first wavelength selective filter for transmitting a first excitation wavelength from the light source to the storage phosphor and the second wavelength selective filter for transmitting a second luminescent wavelength from the storage phosphor to the detector are combined into a single optical element.

18. A miniature dosimeter system according to claim 17, wherein the single optical element is a prism having at least one face which substantially totally reflects blue light wavelengths from the light source away from the storage phosphor which is located on the same or another face of the prism.

19. A miniature dosimeter system according to claim 17 or 18, wherein the single optical element is an optical switch which is capable of being in a first position or a second position wherein the second position blue light wavelengths are directed from the light source to the storage phosphor and in the first position red light wavelengths are allowed to pass from the storage phosphor to the detector.

20. A miniature dosimeter system according to any one of claims I to 19, wherein the autofluoroescence of the optical elements is less than 5,000 photon counts per second.

21. A miniature dosimeter system substantially as herein described with reference to the accompanying drawings.

22. A method of detecting radiation on or around a subject comprising the step of measuring radiation on the subject by way of the miniature dosimeter of any one of the preceding claims.

23. A method of detecting radiation on or around a subject according to claim 22, further comprising measuring radiation on humans or animals or food products.

24. A device for measuring radiation on or around a subject comprising the miniature dosimeter system according to any one of claims I to 21.

25. A device according to claim 24, wherein the device is a radiation detection probe, or is of a substantially rectangular card shape. 21

26. A device according to claim 24 or 25, wherein the device comprises a dosimeter badge and a reader. 22