Abstract:
Applicators for HDR brachytherapy for topical skin treatment which employ multiple channels for radioisotope sources, oriented by the applicator generally parallel to each other and to a desired treatment area skin surface. These applicators provide good radiation exposure uniformity. Filtration of undesirable low energy radiation may be employed using an attached filter element. The applicators are particularly adapted for the treatment of squamous and basal cell skin cancers or other skin lesions. The applicators may provide two or more source guides in various sizes and shapes are described.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to high dose rate (HDR) brachytherapy devices and methods particularly adapted for treating human skin cancers and other conditions, and specifically to applicator components used in such systems and methods for their use in patient treatment. 
       BACKGROUND OF THE INVENTION 
       [0002]    Radiation treatment is very effective for the treatment of squamous cell and basal cell skin cancers for human patients. Historically, superficial 250 KV external beam radiation provided a good tool for such treatment with excellent control and cosmetic results. However, such equipment is no longer available, and is bulky, expensive, and requires highly skilled operators. 
         [0003]    Currently, superficial radiation treatment with electron beams is provided for treating certain skin cancers through a long course of multiple therapy sessions (fractional therapy) which may require daily therapy for several weeks and the depth of the radiation dose for such therapy is usually several centimeters. Such a fractional course is long, expensive, and inconvenient to patients. In addition, cosmetic results from electron beam radiation therapy to the skin are often compromised due to irradiation of subcutaneous tissue underlying the desired treatment site which does not need to be targeted therapeutically. 
         [0004]    In brachytherapy procedures, catheters or guide tubes are used which are, in some procedures a guide tube is used which is positioned externally at a desired orientation relative to a patient&#39;s skin area to be treated. A radioisotope source is loaded into the guide tube and is moved robotically inside the guide tube to topically expose tissue surrounding the source to a desired radiation dose and is thereafter withdrawn. This is referred to as high dose rate or HDR brachytherapy. This procedure is distinguished from low dose rate or LDR brachytherapy in which a radioisotope source is implanted for exposure over a long period (months or years) or implanted permanently. The radiation exposure dose of brachytherapy is intended to cause radiotoxicity and destroy targeted human tissue, for example cancerous skin cells. 
         [0005]    In HDR brachytherapy for treating skin cancer, an applicator component is used which forms a fixture for supporting and orienting a brachytherapy guide tube and further for shielding radiation exposure along ray paths not providing desired exposure of the skin area to be treated. A brachytherapy treatment machine is used to accurately position the radioisotopes source in the guide tube during a treatment session. Typically the position of the radioisotope source is moved within the guide tube after stopping at dwell positions. A control wire inside a flexible brachytherapy guide tube is attached to the guide tube which is in turn mounted to the applicator. The brachytherapy treatment machine moves the radioisotope source to desired dwell positions on a time schedule within the applicator by moving the control wire. 
         [0006]    Single channel brachytherapy applicators for treating skin cancers are known. These devices employed a single guide tube for the radioisotope source. The use of single channel brachytherapy applicators results in uneven radiation distribution to skin surface and superficial depth, resulting in a very high dose in the center area of the applicator as compared to peripheral regions in the treatment field area. Due to limitations of such devices, treatment of skin cancer has been limited due to lack of good applicators with standardized radiation distribution limited to several millimeters in depth. Another known system utilizes a single channel source oriented in a vertical orientation, which is also not conducive to uniform dose distribution pattern; this results in a very uneven dose distribution, relative low dose at center of applicator surrounded by a high dose zone then a very low dose at periphery of treatment area. 
       SUMMARY OF THE INVENTION 
       [0007]    This invention is related to applicators for HDR brachytherapy for topical skin treatment which employ multiple channels for radioisotope sources, which are oriented generally parallel to each other and to the desired treatment area skin surface. These applicators provide good radiation exposure uniformity. Filtration of undesirable low energy radiation may be employed using an attached filter element. The applicators are particularly adapted for the treatment of squamous and basal cell skin cancers or other skin lesions. The applicators are used with HDR brachytherapy treatment machines that are already commercially available. 
         [0008]    Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a pictorial view of an HDR treatment system incorporating one embodiment of an applicator in accordance with the present invention shown during a patient treatment session; 
           [0010]      FIG. 2  is a pictorial view of an applicator in accordance with a first embodiment of this invention shown with installed guide tubes and related components; 
           [0011]      FIG. 3  is another pictorial view of the applicator in accordance with a first embodiment of the invention; 
           [0012]      FIG. 4  is a pictorial view of an applicator in accordance with a second embodiment of the invention; 
           [0013]      FIG. 5  is a pictorial view of an applicator in accordance with a third embodiment of the invention; and 
           [0014]      FIG. 6  is a pictorial view of an applicator in accordance with a fourth embodiment of the invention. 
           [0015]      FIG. 7  is a percent dose distribution graph produced from using an embodiment of the present invention. 
           [0016]      FIG. 8  is a vertical profile plot showing an integrated dose using an applicator in accordance with an embodiment of the present invention along the depth of penetration. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    With reference to  FIG. 1 , an HDR treatment system for topical skin treatment is shown and is generally designated by reference number  10 . Treatment system  10  is shown in a treatment session for a human patient  12 , and principally includes HDR treatment machine  14  with a plurality of flexible tubes  16  coupled to the machine and terminate at guide tubes  18  affixed to applicator  20 . Applicator  20  as illustrated is in accordance with one embodiment of the present invention. 
         [0018]    Applicator  20  is positioned adjacent a desired skin treatment area using jointed holding fixture  22  which can be adjusted to move through many degrees of freedom to properly position applicator  20  as desired for treatment. Fixture  22  has elbow joints which when locked holds the fixture arm  23  in a steady position. Also, at the tip of the arm  23  where the applicator is affixed, there is a micro adjustment system which allows the applicator face to be positioned close to the treatment area skin surface. 
         [0019]    In accordance with known brachytherapy treatment systems, machine  14  is used for and after loading treatment process and is programmed to advance one or more a radioisotope radiation sources (not shown), first through flexible transfer tubes  16  and then into guide tubes  18 . Commercially available HDR Brachytherapy treatments machines like Gamma Med Plus (Varian) and Nucletron High Dose Rate machines are examples of those which may be used with the present invention. As will be described in greater detail in the following text, machine  14  is programmed in accordance with a prescribed treatment plan to accurately move the radiation sources along a prescribed schedule of dwell positions within the guide tubes  18  as desired to provide a desired distribution of radiation exposure over the patient treatment area  24 . In a treatment session, patient  12  is immobilized to the extent necessary to hold treatment area  24  in a fixed position relative to applicator  20  during a treatment session. 
         [0020]    Several embodiments of applicators  20  are described in accordance with the present invention.  FIGS. 2 and 3  illustrate 3 cm diameter applicator  26  in accordance with an embodiment of this invention. As shown applicator  26  forms a concave cavity  28  with a perimeter annular upstanding wall  30  with an enclosed bottom surface  32 . The upper edge of wall  30  forms a flat annular face surface  29 . Not shown is the bottom surface of applicator  26  which is flat. Applicator  26  is preferably formed from a metallic material capable of providing radiation shielding such as tungsten. Three bores  34  are formed through the upstanding wall  30  provided for positioning three rigid guide tubes  18  in position as illustrated in  FIG. 2 . Each bore  34  includes open bore section  35  through wall  30  which are aligned with blind bore sections  37  which do not penetrate through wall  30 . Bores  34  are mutually parallel. Various means for affixing rigid guide tubes  18  in their position in a respective bore  34  can be used such as mechanical set screw type fixing systems. Threaded bores  39  are shown which extend from the outside bottom surface of the applicator and intersect bores  34  which allow a set screw to be installed. Once fixed in position within bores  34 , rigid guide tubes  18  are positioned such that there longitudinal axes are generally parallel to face surface  29  and, during treatment, are parallel to the skin surface at patient treatment area  24 . 
         [0021]      FIG. 2  illustrates applicator  26  with rigid guide tubes  18  affixed in position within bores  34  and shown with detached transfer tubes  16 . Guide tubes  18  may be provided formed of various in different materials, for example stainless steel, titanium, or plastic 
         [0022]    Now with reference to  FIG. 4 , a second embodiment of an applicator  36  in accordance with the present invention is illustrated. Elements and features of applicator  36  which are identical to those of the first embodiment (applicator  26 ) are identified by like reference numbers. Applicator  36  differs from the first embodiment in that it has a smaller diameter; in this case 2 cm, and rather than having bores  34  for three guide channels, it features two guide channels. 
         [0023]      FIG. 5  illustrates applicator  38  which differs from the prior embodiments in that it has an elliptical configuration with its major axes measuring 2×3 cm. This embodiment features three guide channels. 
         [0024]      FIG. 6  illustrates applicator  40  which is generally identical to applicator  38  except that it has a larger diameter of 4 cm. Applicator  40  provides four bores  34  for four guide tubes  18 . 
         [0025]    The following Table 1 provides dimensional features and material for the applicators  26 ,  36 ,  38 , and  40 , identified by their major dimensions as presented previously (i.e. 2 cm is applicator  26 , etc.). In the table, the Outer Height indicates the height of wall  30 , the Inner Height is the height of wall  30  measured on the inside of the concave cavity  28  above bottom surface  32 , and Min. Wall Thickness is the radial thickness of wall  30 . 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Outer 
                 Inner 
                   
               
               
                 Applicator 
                 Applicator 
                 Height 
                 Height 
                 Min. Wall 
               
               
                 Dia 
                 Material 
                 (cm) 
                 (cm) 
                 Thickness 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 2 cm(36) 
                 Tungsten 
                 1.4 
                 1.1 
                 7 mm 
               
               
                 3 cm(26) 
                 Tungsten 
                 1.4 
                 1.1 
                 7 mm 
               
               
                 4 cm(40) 
                 Tungsten 
                 1.4 
                 1.1 
                 7 mm 
               
               
                 2 cm × 3 cm(38) 
                 Tungsten 
                 1.4 
                 1.1 
                 7 mm 
               
               
                   
               
             
          
         
       
     
         [0026]    Table 2 as follows provides additional dimensional specifications for exemplary embodiments of the present invention. In the third column, the maximum distance between the inside surface of the inside of wall  30  and the outermost guide tube  18  is indicated. The last column indicates that a preferred separation distance between the guide tubes  18  and the patient treatment area  24  is 1 cm. Since in most treatment applicator face surface  29  will be placed on or near contact with the patient&#39;s skin, this dimension is also the separation of the planes defined by face surface  29  and guide tubes  18  once installed within the applicator. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 Distance 
                 Distance  
               
               
                   
                   
                 Distance 
                 between 
                 of 
               
               
                   
                 No. of 
                 between  
                 inner  
                 source 
               
               
                   
                 Source 
                 source 
                 wall &amp;  
                 guide tube 
               
               
                   
                 Path 
                 path 
                 outer source 
                 center to 
               
               
                 Applicator 
                 Tubes 
                 tubes 
                 path 
                 skin 
               
               
                 Dia 
                 (18) 
                 (18) 
                 tubes 
                 surface 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 2 cm(36) 
                 2 
                 1 cm 
                 0.5 cm 
                 1 cm 
               
               
                 3 cm(26) 
                 3 
                 1 cm 
                 0.5 cm 
                 1 cm 
               
               
                 4 cm(40) 
                 4 
                 1 cm 
                 0.5 cm 
                 1 cm 
               
               
                 2 cm × 3 cm(38) 
                 3 
                 1 cm 
                 0.5 cm 
                 1 cm 
               
               
                   
               
             
          
         
       
     
         [0027]    The unique design feature of these applicators  26 ,  36 ,  38 , and  40  is that they provide multiple source dwell positions within the applicator cavity which are used to shape the dose distribution patterns as compared to market available applicators which use a single source with a dwell position at the center of the applicator cavity. This design helps us to better control the dose distribution within the area of irradiation. When implying the applicators in accordance with the present invention, the source dwell positions and dwell times are determined in accordance with a radiation treatment plan intended to achieve the desired results. 
         [0028]    When connected to the HDR treatment machine  14 , the radioisotope source stops in multiple dwell positions in each of the source guide tubes  18  within the associated applicator concave cavity  28 . The multiple dwell positions within each applicator cavity  28  allow for better control of radiation dose distribution at the surface and depth of skin when compared to single source-dwell position applicators. 
         [0029]    In order to filter the low energy spectrum of radiation emanating from the radioisotope sources, filter caps of plastics of for example a thickness 0.34 mm may be used. Filter  42  is shown a fixed to applicator  20  in  FIG. 1 . Filter  42  can be formed in a manner that allows the filter to be snap-fit over the opening of the applicator. In one exemplary embodiment of the present invention, the filter material was formed of Derlin monopolymer with a density of 0.051 (ib/in3). 
         [0030]    The following Table 3 illustrate examples of a treatment schedule using the applicators  26 ,  36 ,  38 , and  40  designated by their dimensional characteristic. Table 3 presents dwell positions for radioactive source for the bores  34  identified as Channels 1 and 2 for 2 cm. applicator  36 ; as channels 1, 2, and 3 for applicators  26 , and  38 ; whereas applicator  40  has four Channels 1-4. The position numbers identified as positions #1-3, #1-4 and #1-8 designate dwell positions of the radioisotope source along the path of the channel with the indicated separation between dwell positions (step sizes). Table 3 also provides data for various desired radiation exposure magnitudes identified as 5, 6, and 7Gy (grey). The schedules described in Table 3 are examples of treatment plans which may be prescribed to treat a particular patient treatment area  24 . 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
             
               
               
               
             
               
               
               
               
               
             
               
             
               
               
               
             
               
               
               
               
               
             
               
             
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
             
             
               
                 3.1 
               
             
          
           
               
                 2 cm Circle Skin Applicator 
                   
                   
               
               
                 80 IDL Rounded Aug. 25, 2010 
                   
                   
               
             
          
           
               
                 5 Gy 
                 6 Gy 
                 7 Gy  
                 Position 
                   
               
               
                   
               
               
                 12.8 
                 15.3 
                 17.8 
                 1 
                 CHANNEL 1 
               
               
                 6.5 
                 7.8 
                 9.1 
                 2 
                 (6 mm Step Size) 
               
               
                 12.8 
                 15.3 
                 17.8 
                 3 
                   
               
               
                 12.8 
                 15.3 
                 17.8 
                 1 
                 CHANNEL 2 
               
               
                 6.5 
                 7.8 
                 9.1 
                 2 
                 (6 mm Step Size) 
               
               
                 12.8 
                 15.3 
                 17.8 
                 3 
                   
               
               
                 64.2 
                 76.8 
                 89.4 
                 seconds 
                   
               
               
                   
               
             
          
           
               
                 3.2 
               
             
          
           
               
                 3 cm Circle Skin Applicator 
                   
                   
               
               
                 80 IDL Rounded Aug. 25, 2010 
                   
                   
               
             
          
           
               
                 5 Gy 
                 6 Gy 
                 7 Gy 
                 Position 
                   
               
               
                   
               
               
                 10 
                 12 
                 14 
                 1 
                 CHANNEL 1 
               
               
                 4.6 
                 5.6 
                 6.5 
                 2 
                 (5 mm Step Size) 
               
               
                 4.6 
                 5.6 
                 6.5 
                 3 
                   
               
               
                 10 
                 12 
                 14 
                 4 
                   
               
               
                 12.1 
                 14.5 
                 16.9 
                 1 
                 CHANNEL 2 
               
               
                 3.1 
                 3.8 
                 4.4 
                 2 
                 (5 mm Step Size) 
               
               
                 1.6 
                 1.9 
                 2.3 
                 3 
                   
               
               
                 1.6 
                 1.9 
                 2.3 
                 4 
                   
               
               
                 3.1 
                 3.8 
                 4.4 
                 5 
                   
               
               
                 12.1 
                 14.5 
                 16.9 
                 6 
                   
               
               
                 10 
                 12 
                 14 
                 1 
                 CHANNEL 3 
               
               
                 4.6 
                 5.6 
                 6.5 
                 2 
                 (5 mm Step Size) 
               
               
                 4.6 
                 5.6 
                 6.5 
                 3 
                   
               
               
                 10 
                 12 
                 14 
                 4 
                   
               
               
                 92 
                 110.8  
                 129.2  
                 seconds 
                   
               
               
                   
               
             
          
           
               
                 3.3 
               
             
          
           
               
                 4 cm Circle Skin Applicator 
                   
                   
               
               
                 80 IDL Rounded Mar. 7, 2012 
                   
                   
               
             
          
           
               
                 5 Gy 
                 6 Gy 
                 7 Gy 
                 Position 
                   
               
               
                   
               
               
                 11.7  
                 14 
                 16.3 
                 1 
                 CHANNEL 1 
               
               
                 6.7 
                 8 
                 9.3 
                 2 
                 (5 mm Step Size) 
               
               
                 5.0 
                 6 
                 7 
                 3 
                 Origin 1 mm 
               
               
                 6.7 
                 8 
                 9.3 
                 4 
                   
               
               
                 11.7  
                 14 
                 16.3 
                 5 
                   
               
               
                 11.7  
                 14 
                 16.3 
                 1 
                 CHANNEL 2 
               
               
                 5.8 
                 7 
                 8.2 
                 2 
                 (5 mm Step Size) 
               
               
                 2.9 
                 3.5  
                 4.1 
                 3 
                 Origin 0 mm 
               
               
                 2.1 
                 2.5  
                 2.9 
                 4 
                   
               
               
                 2.1 
                 2.5  
                 2.9 
                 5 
                   
               
               
                 2.9 
                 3.5  
                 4.1 
                 6 
                   
               
               
                 5.8 
                 7 
                 8.2 
                 7 
                   
               
               
                 11.7  
                 14 
                 16.3 
                 8 
                   
               
               
                 11.7  
                 14 
                 16.3 
                 1 
                 CHANNEL 
               
               
                 5.8 
                 7 
                 8.2 
                 2 
                 2 3 
               
               
                 2.9 
                 3.5 
                 4.1 
                 3 
                 (5 mm Step Size) 
               
               
                 2.1 
                 2.5  
                 2.9 
                 4 
                 Origin 0 mm 
               
               
                 2.1 
                 2.5  
                 2.9 
                 5 
                   
               
               
                 2.9 
                 3.5  
                 4.1 
                 6 
                   
               
               
                 5.8 
                 7 
                 8.2 
                 7 
                   
               
               
                 11.7 
                 14 
                 16.3 
                 8 
                   
               
               
                 11.7  
                 14 
                 16.3 
                 1 
                 CHANNEL 4 
               
               
                 6.7 
                 8 
                 9.3 
                 2 
                 (5 mm Step Size) 
               
               
                 5.0 
                 6 
                 7 
                 3 
                 Origin 1 mm 
               
               
                 6.7 
                 8 
                 9.3 
                 4 
                   
               
               
                 11.7 
                 14 
                 16.3 
                 5 
                   
               
               
                 173.6 
                 208 
                 242.4 
                 seconds 
                   
               
               
                   
               
             
          
           
               
                 3.4 
               
             
          
           
               
                 Ellipse Skin Applicator 
                   
                   
               
               
                 80 IDL Rounded Aug. 25, 2010 
                   
                   
               
             
          
           
               
                 5 Gy 
                 6 Gy 
                 7 Gy 
                 Position 
                   
               
               
                   
               
               
                 14.9 
                 17.9 
                 20.9 
                 1 
                 CHANNEL 1 
               
               
                 14.9  
                 17.9 
                 20.9 
                 2 
                 (9 mm Step Size) 
               
               
                 12.5 
                 15.0 
                 17.5 
                 1 
                 CHANNEL 2 
               
               
                 0.0 
                 0.0 
                 0.0 
                 2 
                 (8 mm Step Size) 
               
               
                 12.5 
                 15.0 
                 17.5 
                 3 
                   
               
               
                 14.9 
                 17.9 
                 20.9 
                 1 
                 CHANNEL 3 
               
               
                 14.9  
                 17.9 
                 20.9 
                 2 
                 (9 mm Step Size) 
               
               
                 84.6 
                 101.6  
                 118.6 
                 seconds 
                   
               
               
                   
               
             
          
         
       
     
         [0031]    Now with reference to  FIG. 7 , an exemplary percent dose distribution (PDD) plot is shown which illustrates the integrated distribution of radiation across an applicator in accordance with this invention. The distribution integrates exposure of the radioisotope sources measured on the plane of patient treatment area  24  as they move along the guide paths in accordance with a schedule such as that described previously for 2 cm. applicator  36 . The dose distribution plot shows a high degree of uniformity across the cross section of the patient treatment area  24 . This is a primary feature of applicators in accordance with this invention as it is desirable to achieve a desired dose and apply the distribution uniformly across the patient treatment area  24 . 
         [0032]      FIG. 8  shows an integrated dose distribution as a measured along the depth the present penetration, starting from the skin surface of patient treatment area  24  to deeper tissue. The curve shows a dramatic exposure drop off from the surface, which is a desirable attribute since the intent is to treat diseased tissue at the surface of the patient skin and it is not intended to penetrate deeper where underlying subcutaneous tissue can be damaged by undesired radiation exposure. 
         [0033]    While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.