in the drawings , fig1 shows somewhat schematically an applicator 10 according to one embodiment of the invention , the applicator including a flexible control line or cable 12 leading from a controller , not shown , and a catheter or applicator portion 14 . a balloon 16 of the applicator and catheter is shown inflated in fig1 . the applicator device is generally as shown in co - pending application ser . no . 10 / 683 , 885 , filed oct . 13 , 2003 . as shown , at the proximal end 18 of the applicator is a branch 20 . the three ports 22 , 24 and 26 of this branch device may comprise a service port , a drainage port and a balloon inflation port , respectively . the functions of these ports are explained further below with reference to other drawings . a flexible main shaft 28 extends from the branch device 20 to the balloon 16 , and is sealed to the balloon at 30 . the balloon in fig1 is shown partially cut away to reveal an electronic x - ray source 32 within the balloon , at the end of the control line 12 and moveable longitudinally within the balloon 16 and catheter 10 . in preferred embodiments the x - ray tube 32 is less than 4 mm in diameter , preferably no greater than about 3 to 3 . 2 mm in diameter , and in some embodiments this tube is as small as 1 mm in diameter or even smaller . the shaft 28 is flexible , and may be highly flexible and pliable near the proximal end 18 , as explained in the co - pending application referenced above , for the purpose of folding the applicator over against the breast when not in use , when the control line 12 and x - ray source 32 are not inserted into the applicator , particularly for breast irradiation involving several dose fractions such that the applicator need not be removed between fractions . the flexible shaft provides a lumen for admitting a fluid to inflate the balloon 16 , while also providing a duct or lumen for insertion of the radiation source 12 , via guides connected to the balloon . the shaft 24 also preferably provides a channel for drainage of liquids from the body cavity within which the applicator is inserted . a drainage receptacle can be connected to the end of the drainage port or an aspirator can be used when needed to withdraw liquids . the applicator 10 is shown schematically in fig2 and 4 as inserted into a resection cavity of a breast for treatment . fig5 a , 5b and 5 c show the applicator 10 in greater detail , and with the balloon 16 deflated and collapsed . the service port 22 , in line with the flexible shaft 28 , as well as the drainage port 24 and the balloon inflation port 26 , are illustrated . also shown is a distance scale preferably included , with distances shown at 6 cm , 7 cm , 8 cm , etc ., up to about 15 cm , to indicate to the physician the total depth of the applicator into cavity and opening wound . this provides a direct and easily used means to determine the position of the distal end 35 of the applicator as it is being inserted . as shown in fig5 b and 5c , drainage is provided for the resection cavity via drain holes 36 at the distal end 35 of the applicator , beyond the balloon 16 , communicating internally to the drain port 24 , and also preferably via drain holes 38 shown just proximal of the balloon , for draining fluids which travel over the surface of the balloon . as in co - pending application ser . no . 10 / 683 , 885 , the balloon preferably has some form of liquid channeling means on its outer surface . this could be a multiplicity of bumps , allowing for liquid travel even though the balloon is engaged against the tissue , or a series of longitudinal ridges on the balloon surface to form channels . the drain holes 38 catch most of the liquid flowing in this manner , and these holes communicate with the drain port 24 . the balloon 16 may advantageously be formed of a silicone material , although other appropriate biocompatible materials can be used . the balloon material is bonded to the outside surface of the flexible shaft 28 in sealed relationship thereto , by known procedures . fig2 and 4 indicate somewhat schematically the use of the applicator device 10 in a resection cavity of a human breast 41 , for radiation therapy . in fig2 the catheter 10 is shown with its balloon 16 shown in dashed lines , and the shaft 28 in the balloon forming a guide for an x - ray source which may either be a miniature x - ray tube or an isotope . a seal 40 is shown in fig2 , for sealing the flexible shaft 28 of the catheter / applicator against the surface of the skin where it enters the body . also shown in fig2 is a connector 42 for connecting the applicator shaft , via the service port 22 , to an exterior cable 44 that contains the control cable 12 , leading to the controller ( not shown ) for the applicator and for the x - ray source , if the source is a controllable miniature tube . fig3 and 3 a illustrate the ability of the invention to achieve a more exact dose profile by use of a miniature electronic x - ray source in the applicator 10 , a source which is capable of voltage variation and thus variation of the depth of dose . as one rather simple example , four dwell positions are shown in fig3 and represented in a bar graph in fig3 a . the deepest dwell position , position 1 , is closest to the lungs of the patient . thus , the voltage is relatively low for this dwell position , controlling the depth of penetration into the surrounding tissue such that radiation will not reach the lungs to any appreciable degree . the second dwell position is farther from the lungs , and fig3 a shows that the voltage is increased for this dwell position , for a greater depth of penetration . similarly , dwell positions 3 and 4 are progressively farther from the lungs and the voltage and depth of dose are progressively higher . fig4 and 4 a illustrate schematically the use of a switchable , controllable electronic x - ray source in the catheter 10 , wherein current is varied at different dwell positions in order to vary the dose intensity at different positions . in the schematic drawing of fig4 , four different dwell positions are again indicated for the electronic x - ray source , within the balloon 16 of the catheter 10 , the balloon positioned in a resection cavity in a patient &# 39 ; s breast 41 . the control current does not vary the depth of penetration of the radiation , only the dose intensity . in the illustrated procedure , the current is varied in order to produce a uniform isodose profile . thus , at positions 1 and 4 where the x - ray source is closest to tissue , the current is set at a lower level , while at dwell positions 2 and 3 , close to the center of the balloon 16 and of the resection cavity , where the tube is more distant from tissue , the current is set higher . note that dose intensity can be controlled also by controlling the length of time the source is “ on ” at each dwell position , or simply by controlling the length of dwell at each position assuming the source remains “ on ”. these profiles of fig4 to 5 a are just examples of how the variation of voltage and current using an electronic x - ray source can be beneficially used accurately to create a required isodose profile . fig6 and 7 illustrate the balloon 16 having an x - ray contrast medium in or on the balloon wall . as explained above , this differs from prior practice in which a saline solution within the balloon contained a weak solution of contrast medium so that the balloon would show up in external x - ray imaging , for location of the balloon . in this case the contrast medium is only in or on the balloon wall , and this medium will absorb radiation , indicated at 46 , during external imaging ; it will also absorb radiation from the therapeutic source and thus will attenuate the radiation delivered from inside the balloon to some extent . however , with a low concentration of such contrast medium in the balloon wall , the attenuating effect of the medium for radiation passing through the balloon at an angle normal or generally normal to the balloon wall will be small and essentially negligible . on the other hand , the effect of radiation , particularly x - ray radiation , passing tangentially through the edges of the balloon as indicated in fig6 and 7 , will be at a maximum , since the radiation must pass through the balloon edge wise at this tangential angle , a much longer effective path length . the result is that a balloon 16 with such contrast medium can be located by external x - ray , visible in an x - ray image by its edges . this is demonstrated in fig7 showing effective path length of x - rays through balloon material as a function of distance from the center of the balloon . the densest outline of the balloon will be at its circumference , especially at distal and proximal ends of the balloon itself , where the wall material may be somewhat thicker at its attachment to the flexible shaft 28 and in any event , where the balloon has areas that are stretched far less due to the geometry of the balloon and its attachment to the flexible shaft 28 of the catheter device . fig6 shows in a schematic approximation a graph of x - ray density ( darkness or density of the line appearing in an x - ray image ) on a vertical axis , versus position . for clarity the balloon 16 is represented directly adjacent to the graph , and showing the direction of x - ray radiation 46 . as illustrated , density is low in the x - ray image of the balloon at a region 48 in fig6 where the radiation passes generally normally through the balloon wall ; however , spikes of extreme density are shown at 50 and 52 , where the rays must pass through considerable distance of the balloon wall on edge . as can be seen from the graph of fig7 ( showing effective path length through both 4 and 5 cm diameter balloons ), the effective path length at these tangent regions can be about 15 to 25 times greater than the normal path length . thus , the contrast - doped balloon wall provides a far superior imaging arrangement than the prior saline solution , without adversely affecting therapeutic radiation . the procedures and apparatus described above are applicable to natural body cavities ( e . g ., bladder , uterus , vaginal ), and naturally occurring lumens , as well as surgically created cavities . the term cavity in the claims is intended broadly to refer to natural or surgical cavities or lumens . also , except where a switchable x - ray source is specifically called for herein for the advantages it offers in modulation or other purposes , the described procedures can ordinarily be performed using isotopes . the term brachytherapy device refers to either type of radiation source . 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 .
methods and apparatus are described for irradiating living tissue via a cavity or lumen , using an inflatable balloon applicator . in a preferred embodiment the applicator balloon has a balloon skin with x - ray contrast material in relatively low concentration , so that an outline of the balloon will appear sharply when imaged externally . in another preferred embodiment the balloon catheter has a drain for withdrawing liquids from the cavity , which may include channels or texture on the exterior of the balloon . methods are described for using a switchable miniature x - ray tube , variable as to voltage and current , to achieve accuracy in an isodose profile .