Patent Application
20100074407
This invention relates to the field of radiation therapy by means of ionizing radiation energy applied to tumors or other imperfections in skin or near-skin tissues, or in or near other exposed anatomical surfaces.
For many years, a variety of skin or near skin medical conditions have been treated by application of superficial voltage (50-150 kV) or orthovoltage (150-500 kV) x-ray therapy. These methods have drawn criticism because their penetration depth often puts deeper tissues at risk. As a result, external electron-beam radiation has come into greater use because its characteristic penetration can more easily be controlled. Such radiotherapy often follows surgery to excise a tumor or other defect. Often, the radiation apparatus used for electron beam treatment purposes is large, unwieldy, and incapable of being directed to the lesion with precision. Because it is designed to deliver high-energy radiation, the patient usually must be extensively shielded except for the area of the tumor, and radiation safety may require such apparatus only be operated from within a shielded room or “bunker”, from which all personnel other than the patient must be excluded during active treatment. This creates a situation which can be highly intimidating or claustrophobic for the patient. Because of the capital investment required for such an installation, this sort of treatment is often unavailable in small clinic or office situations. Reduction in capital expenditure requirements and intimidation factors would be great improvements over current external beam practice.
Furthermore, the available radiation output levels from such equipment may greatly exceed those required for the intended treatment, and output patterns are generally fixed. These output characteristics usually necessitate that the tumor be covered with radiation absorbing material such that the radiation intensity incident on the skin is more appropriate for the desired treatment. In addition, any necessary collimation of the radiation pattern to accommodate the patient's treatment requirements would be accomplished by conventional methods known to those of skill in the art.
In use, the machine is positioned properly over the patient to assure protection of adjacent normal tissues, with the collimated beam passing through secondary shielding which is directed at the subject tumor site. The patient must not move once alignment is determined, otherwise the treatment is not delivered to the desired area. When all is ready, the therapist leaves the room, and treatment is initiated. Because of the number of parameters in play to produce a satisfactory treatment and the complexity of the treatment setup, the potential for error and therefore imprecision in dosage delivery is significant. Clearly, smaller apparatus specifically designed for treatment of lesions and not requiring such extensive setup, treatment expense or safety precautions would be preferred to the apparatus and methods described above.
Contact applicators, usually including tungsten shielding, have been developed which utilize isotope (usually iridium) radiation sources (See Nucletron, Columbia, Md. 21046.) These applicators are difficult to position accurately over the lesion or imperfection to be treated, and as with high energy x-ray treatment, the characteristic penetration depth of iridium may well compromise underlying tissue. Use of isotopes like iridium in this manner will also require that treatment be carried out within a bunker as described above.
It is an object of this invention to provide methods for identifying the region to be treated on the patient, planning the radiation therapy quantitatively to be administered within that region, and executing the therapy conveniently, and in a timely manner. A further object of this invention is to provide a method of treatment of surface lesions and imperfections utilizing x-rays having controlled, minimal depth of penetration and which eliminate many of the safety concerns common to prior art methods as described above. A further object is to provide a convenient applicator which can be positioned over the lesion or imperfection to be treated under direct visualization, assuring proper treatment of diseased tissues, but sparing adjacent tissues. Still further, it is an object of this invention to provide a record of the therapy delivered, and to verify that the treatment was to plan.
Specifically, this invention encompasses methods for treatment of skin or near-skin lesions or imperfections and is directed to the use of small ionizing radiation sources, preferably miniature x-ray sources comprising elements such as those described in U.S. Pat. Nos. 6,319,188, 7,127,033 and/or 7,158,612, all of which facilitate such radiation therapy in small clinical settings and are herein incorporated in their entirety by reference. The preferred x-ray energy level is in the range of up to about 50 kV, with preferred treatment depths between the tissue surface and 5 mm depth. Such x-ray sources can be modulated with regard to penetration depth by varying x-ray tube voltage, and to incident dose intensity by varying tube current, although in practice, it may be preferable to adjust exposure time rather than varying tube current to achieve a prescribed absorbed dose. These sources can in general be switched on and off as needed. The principles underlying such tubes may be found in Atoms, Radiation and Radiation Protection,
Second Edition, by James E. Turner, printed by John Wiley & Sons, 1995, incorporated herein in its entirety by reference.
The preferred embodiment of this invention further comprises an applicator incorporating provision for positioning the radiation beam over the region to be treated under direct visualization. The applicator comprises a base, preferably of stainless steel, and optionally a thin polymeric cover on the working side of the base, having a generally planar distal face substantially in contact with the skin. In the center of the base is a window of a size and shape to expose the lesion to the radiation emitted from within the applicator. The window size and shape may be chosen by the therapist to suit the therapeutic needs of the patient, via interchangeable bases. Except for the window, the base is substantially radio-opaque. We have found a thickness of stainless steel adjacent the window on the order of 2 mm adequate to provide sufficient attenuation in a typical therapeutic situation. More highly attenuating materials, for example tantalum, would permit thinner sections having the same levels of attenuation.
Proximal of the base of the preferred embodiment is an optically transparent housing preferably of leaded acrylic polymer (Nelco, Woburn, Mass.), or equivalent, through which the therapist may view the window overlying the lesion to achieve the alignment desired for therapy delivery. The attenuation of the leaded acrylic is preferably about 1/24 that of solid lead for equivalent thickness. The thickness of the acrylic housing therefore needs to be on the order of about 6 mm to sufficiently attenuate the back-scattered radiation. In positioning the applicator the therapist's view may be distorted, but it is still easy to observe and assure that the window circumscribes the desired treatment area. In an alternative embodiment without direct visualization, the housing may be of stainless steel or other materials as is further discussed below. In other respects, the embodiments are similar. In all embodiments described herein, it is preferable that elements in contact with or near the patient be capable of convenient sterilization, or be one-time-use components.
The base and housing generally share a common axis which is substantially transverse to the area of skin to be treated. Proximal of the housing is a cup-shaped filter of a low Z material, for example aluminum (or other materials in accordance with the isodose shaping discussion below), and proximal of that, a tubular source guide leading to other treatment system elements including a source power supply and controller. The source guide contains the source on the end of its cable and any utilities or support functions necessary to operate the x-ray tube, such as the coolant and cooling apparatus necessary to cool the x-ray source tube. See U.S. Pat. No. 7,127,033.
The aluminum filter may be contoured so as to shape the isodose patterns (imaginary surfaces of constant dose intensity), for example to flatten them, at the window where the radiation is incident on the skin, as well as distal of the applicator within the patient's body at or about the prescribed treatment depth. Further, the filter serves to strip off any low energy portions of the x-ray tube spectrum, hardening the beam in a conventional manner. The low energy elements of the unhardened spectrum are generally absorbed by the skin or other tissue which the beam initially encounters. With a hardened beam lacking these low energy components, the dose absorbed by the skin is reduced which may have cosmetic advantages or may even prevent substantial tissue inflammation.
In instances where the prescription is specified as a skin dose, alternate filter materials, for example silver or molybdenum, can also be designed to shape the x-ray intensity patterns as described above. We have found that filters of these materials essentially do not harden the beam and leave the energy spectrum substantially unaltered. That means a similar beam shaped by a silver or molybdenum filter is more quickly absorbed at the skin with less energy absorbed at depth. Such attenuators are discussed in more detail in co-pending U.S. patent application Ser. No. 12/072,620, and that application is incorporated herein in its entirety by reference.
When assembled and positioned properly over the lesion to be treated, the applicator may be held in position manually, clamped with respect to the operating table upon which the patient is lying, clamped with respect to the patient and his/her lesion, or otherwise supported.
In an alternate embodiment, the base and/or window element may be eliminated, and the leaded acrylic housing may be in direct contact with the skin surrounding the lesion.
In a further preferred embodiment, the applicator is similar to either of the descriptions above, but without optically transparent elements and therefore without provision for direct visualization. The applicator can optionally include targeting or reference marks which can be aligned with marks or features on the patient near the lesion to be treated.
In a still further embodiment, the applicator can be used in conjunction with a flexible shield (see U.S. patent application publication No. 2007/0075277, for example, incorporated herein in its entirety by reference) having a window of the desired shape which is positioned on the patient to expose the lesion to be treated, and to protect adjacent tissue. The applicator is then placed over the window and held in position as described above.
In all embodiments described above, the shape of the treatment window can be custom shaped to suit a given patient or lesion, or may be a member of a standard set of window shapes supplied as a kit. In the case of the flexible shield which can for example be of tungsten-loaded silicone rubber, a variety of silk-screened window patterns may optionally be printed on the sheet as supplied, such that the therapist can cut out a window in the shield to suit the case at hand.
Furthermore, a beam shaping filter can be used in conjunction with the applicator embodiments described above to harden or not harden the transmitted x-ray beam, and/or to shape the isodose patterns to suit the prescription for the case at hand. The applicator can also be instrumented to control the progression of the therapy, including in real time, or to create a record of the therapy delivered for inclusion in the patient's records. These and other objects, features and advantages of the invention will be apparent from the attached drawings and description of preferred embodiments which follow.
a, b, and c show schematically various filters used to shape the x-ray beam emitted when used in conjunction with embodiments of the invention.
a and b show various silk-screened window patterns that can be placed on the surface of a flexible shield used in conjunction with applicators and/or methods of the invention.
Note also, the removable (and optionally interchangeable) window element 108 could be secured directly to the housing 104 if desired, by threads, machine screws, snap-on or otherwise.
An optional x-ray-transparent, thin polymeric cover 114 is snapped onto the distal face of the window element 108. This cover provides a level of cleanliness, and can be used to retain a radio-chromic film (not shown) as is discussed below. In use, the window element 108 (or cover 114, if present) is in contact with the patient's skin and positioned such that the lesion to be treated is exposed in the window 112. When in contact with the skin as described, the base and window element control both the shape and size of the incident beam onto the patient's skin, and substantially attenuate the beam elsewhere.
Proximal of the acrylic housing 104 is a flanged sleeve 116, the flange of which is used to secure the flanged sleeve to the acrylic housing 104 by screws 118. Internally at its proximal end, the flanged sleeve 116 is fastened by screw threads 120 to an adapter 122. The adapter serves several purposes. At its proximal end, the adapter 122 is permanently secured to the distal end of a source guide 124 as shown, by brazing, welding or silver soldering. Other conventional fastening methods, including by non-permanent screw-threads could also be used. The source guide could be non-metal.
The adapter 122 extends distally through the lumen of the flanged sleeve 116 to external threads 126 used to mount a cup-shaped radiation filter 128 which has an internally threaded ring or rim 129. Details of the radiation filter are discussed in greater detail below. If desired to protect the acrylic housing from undue radiation exposure, the distal end of the flanged sleeve 116 may be extended or configured relative to the filter in order to form an aperture limiting the spread of radiation within the housing such that radiation directly incident on the internal surface of the housing is reduced or eliminated.
Note that the assembly shown and described constitutes one preferred way of connecting the source guide 124 to the housing 104 and base 102; other types of assemblies can be employed, preferably providing for a filter 128, most preferably an interchangeable filter.
Through the source guide 124, a source catheter 130 is advanced until it abuts the inner side of the face of the radiation filter 128. Within the source catheter are the source 132 mounted on its cable 134, and any necessary x-ray tube utilities or apparatus necessary to support its proper functioning.
In use, the therapist selects the window (from a plurality of sizes and/or shapes) appropriate to the case at hand and determines the prescription to be delivered. A series of different window elements 108 can be provided. If treatment merely consists of an x-ray intensity level and treatment time, the necessary parameters are input to the system for delivery of the prescription. If the prescription is more complicated, the necessary settings for treatment delivery may be preset or noted in a convenient manner for manual control. Preferably, the treatment plan may be entered into an automated controller (not shown) as part of a treatment system such that once initiated, the prescribed treatment is delivered automatically.
Next, the elements of the applicator and source are assembled, and made ready for treatment delivery. The assembled apparatus is positioned over the skin area to be treated. By viewing the skin area through the housing (at least a portion of which is substantially optically transparent in a preferred embodiment), the operator correctly locates the applicator over the lesion to be treated. The applicator is then clamped in place, or alternatively, held in position manually, and treatment is initiated. At the conclusion of treatment, the x-ray emissions are switched off, and the apparatus is removed from the patient.
a, b and c show variations in filter designs, and in general, the differences in isodose shapes which result.
As described in the summary above, and in the aforementioned co-pending application Ser. No. 12/072,620, most low Z filter materials, such as aluminum for example, serve to conventionally harden the x-ray beam, that is they strip off low-energy portions of the emitted spectrum, which tightens the energy spectrum of what is transmitted through the filter. Since energy equates to penetration depth, such filters can be tuned to target a narrow penetration depth, thereby reducing the dose absorbed at the skin. As described in the referenced application, we have found that a few filter materials, notably silver and molybdenum, have little effect on the energy distribution of the transmitted beam, and can be effectively used where a skin dose is required, and to reduce the dose absorbed at depth. The beam shaping principles are the same with either sort of materials, but the ranges over which they are most useful to the therapist differ.
a shows in plan view, a flexible shield 180 of tungsten-loaded silicone rubber, or as might otherwise be described in co-pending U.S. patent application No. 2007/0075277. Silk-screened on the surface is an exemplary pattern of radial lines 182 emanating from a center position which can be used for orienting the shield, and concentric, circular pattern of lines 184 which can be used by the therapist as a guide for cutting windows responsive to the patient's prescription and needs. When so prepared, the shield can be used to form a treatment window rather than using the window element 108 described above. Such use may eliminate the need for direct visualization through the applicator housing 104 or housing 152 during placement since the shield and window can be placed and secured over the lesion first, followed by positioning of the applicator using the silk screened lines on the shield for guidance. The outer silk-screened circle 185 may be sized to correspond with the outside diameter of the window element 108 of the applicator 100, or of the polymer cover 114 if present (see
Without the need for visualization, the preferred applicator embodiment would be as shown in
A flexible shield 180 (
b depicts a flexible shield 186 similar to that of
Several different combinations of features have been incorporated in the different embodiments described above. In principle, these may be included in different combinations, or the elements arranged in different configurations relative to one another but such that the functions of each are still effective.
The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.
