Patent Number: 
Section: description

Turning to the drawings and particularly FIG. 1, there is shown a schematic of a female patient (shown in phantom) undergoing localized radiotherapy from a radiation source such as a collimator 5. A first embodiment of a radiation shield 100 of the invention is illustrated in use with an optional support stand assembly 200. As shown in phantom, tangential radiotherapy beams 72 originating from a collimator 5 are shown targeting the treatment region of the patient. The shield device 100 is shown shielding the patient""s contralateral chest region from the scattered radiation of the radiotherapy beams 72 and collimator 5. However, the shield 100 may be sized and shaped to shield other patient areas such as the thyroid, testes, ovaries and the brain. As shown in FIG. 2, the shield 100 of a first embodiment of the invention comprises a rectangular plate preferably shaped to conform to a patient""s anatomy and which is dimensioned to have a sufficient length L and width W to shield the adjacent region of the treatment area of the patient undergoing radiotherapy. For example, where the shield 100 is utilized to shield the contralateral breast of a female patient, the width W of the shield 100 is generally in the range of about 15 to about 30 centimeters, with a preferred range of about 20 to about 25 centimeters. Further, the length L of the shield 100 is generally in the range of about 15 to about 40 centimeters, with a preferred range of about 30 to about 35 centimeters. However, other dimensions of the shield may be utilized in order to tailor the shield to other anatomical sites such as the male testicular region. The shield 100 is primarily comprised of a radiation absorbing material or any non-radioactive material having a high atomic number such as, but not limited to, lead, gold, tungsten, depleted uranium, or cerabend. Preferably, the shield material is lead. The shield 100 has an optional exterior surface layer 104 which is comprised of any suitable material such as rubber, polymeric, acrylic or other soft compressible material. Preferably, the exterior surface layer is comprised of polystyrene or other suitable material capable of absorbing low energy photons electrons. Preferably, the exterior surface layer has a minimum thickness in the range of about 0.10 to about 10 centimeters, and is vacuum molded or glued to the exterior surface of the radiation absorbing material 102. The shield 100 further comprises a front or leading edge section 106, a mid section 108, and a rear section 110. The leading edge section 106 is preferably shaped such that the inner surface 112 of the shield 100 is capable of being placed in close proximity to the patient""s skin, and preferably shaped to conform to the curvature of the anatomy of the site which is being shielded. For example as shown in FIG. 3, the curvature of the inner surface 112 of the shield 100 has been designed to match the breast curvature 132 of 95% of the female population as shown in FIG. 4. The estimated curvature 132 of the female population was determined experimentally by averaging the measurements of the breast curvature of a random selection of fifty female patients. It is further desired that the leading edge section 106 have smooth rounded edges in order to facilitate placement of the shield 100 in close proximity to the patient""s skin. The upper surface 114 of the leading edge section 106 is additionally shaped such that the exterior edge 116 of the leading edge section 106 may be placed in close proximity to the medial tangential field 72 (i.e., tangential radiation treatment beam) without interfering with the path of the radiation beam. This positioning of the shield 100 is especially desirable since the region of the patient nearest to the beam receives the highest scattered radiation exposure. As shown in FIG. 3, this may be accomplished by shaping or angling the upper surface 114 of the leading edge section 106 such that the surface 114 is approximately parallel or tangent to the radiotherapy beam 72. Thus, the treatment or gantry angle of the radiotherapy treatment field has been taken into consideration in the design of the leading edge 106 of the shield 100. It is important that the leading edge section 106 of the shield 100 have a sufficient thickness of the radiation absorbing material 102 in order to protect the patient, yet be thin enough to be positioned as close as possible to the treatment area without interfering with the treatment beam. The preferred thickness of the leading edge 106 of the shield 100 was determined by experimentally measuring the average clearance distances of 50 patients undergoing radiotherapy treatment for breast cancer. The clearance distance is defined as the perpendicular distance between the medial tangential treatment field and the patient""s skin as measured along the contra-lateral surface of each patient. Thus, it is preferred that the leading edge be tapered such that the thickness of the radiation absorbing material tapers from the mid-section 110 to the distal end or edge 116 of the leading edge section 108 such that the thickness of the shield does not exceed the corresponding clearance distances. Thus as further shown in FIG. 4, curve 134 illustrates the height (i.e., the summation of the clearance and breast curvature data) of the leading edge of the shield 100 in relationship to the breast curvature 132 of the patient. The allowable thickness of the shield 100 is the difference between these two curves. The leading edge section 106 preferably has a thickness in the range of about 2.0 to about 4.0 centimeters. It is more preferable that the leading edge thickness be in the range of about 2.0 to about 3.0 centimeters. This tapered edge design 114 allows the shield 100 to be placed as close as possible to the medial treatment field without interfering with the treatment beam 72. For example as shown in FIG. 6, the leading edge of the shield may be designed to vary in thickness from 0.0 cm at the medial field border of the patient to approximately 3.0 cm at a distance of 4.0 cm from the medial field border based on the clearance measurements. This leading edge design results in a scattered radiation reduction of at least 90% at 1.0 cm from the medial field border. After 4.0 cm from the medial field border, there are no constraints on the thickness and the shield was designed as a constant thickness of 2.0 cm extending out to 30 cm, which would reduce the externally scattered radiation by at least 95%. As shown in FIGS. 5a and 5b, the shield 100 may additionally comprise other cross-sectional shapes such as, but not limited to, a wing or symmetrically curved plate. For a wing cross-sectional shape as shown in FIG. 5a, the thickness of the shield tapers from the leading edge 116 to the trailing edge 128. At the leading edge section 106, the minimum radiation absorbing material thickness is in the range of about 2.0 to about 4.0 centimeters. Preferably, the leading edge radiation absorbing material thickness is in the range of about 2.0 to about 3.0 centimeters. This shaping feature of the invention significantly reduces the weight of the shield 100 since the radiation absorbing material is placed only where needed, so that the highest energy components of the scattered radiation are effectively attenuated by the thickest part of the shield. As shown in FIG. 5b, the shield may also comprise a curved plate preferably having a curved shape to conform to the anatomy of the patient""s area to be protected. The curved plate further preferably has smooth rounded edges. All of the above described embodiments of the shield may further comprise a cutout section or cavity 160 located in the mid-section 108 of the shield 100 on the interior surface 112 which lies adjacent the patient""s skin in order to facilitate placement of the shield in closer proximity to the tangential beam 72. This cavity 160 may further be lined with a layer of soft compressible material 162 such as foam or a gel pack which can conform to the patient""s shape or contour as well as provide an increased level of comfort to the patient. The embodiments of the shield 100 may be further provided with a plurality of dosimeters or radiation sensing devices 140 mounted on the exterior surface 114 of the shield 100 preferably on the leading edge section 106, as well as along the interior surface 112 of the shield. The dosimeters may preferably be of a thermoluminescent-type such as Model Number TLD-100 manufactured by Bicron, Inc. The dosimeters 140 mounted on the interior surface 112 are utilized to estimate the amount of radiation dose which is transmitted through the shield 100 near the patient""s skin. These internally mounted dosimeters 140 may preferably be connected in a systematic manner with the collimator 5 such that the machine could be automatically switched off if the patient""s radiation dose exceeds a predetermined level. Alternatively, the interior mounted dosimeters 140 may be connected to an enunciator panel and readout display panel to give warnings to medical personnel if the patient is receiving a radiation dose above or below predetermined levels. The internally mounted dosimeters could also be used to track the patient""s cumulative dose over the treatment period. Further, the exterior mounted dosimeters 140 may also be connected to a display panel to alert medical personnel when the measured radiation level exceeds a predetermined level in order to indicate that the shield 100 is improperly located within the radiation treatment field. Thus both the externally and internally mounted dosimeters 140 may facilitate placement of the shield 100 on the patient and allow for positional adjustments should the patient be receiving too much scattered radiation dose to the contralateral area or if the shield is misplaced within the treatment area. The shield device 100 may further optionally comprise a support stand assembly 200. The support stand assembly 200 is supported by a conventional base 210 having three or more legs 220, with one of the legs 220 further comprising a counterweight 230, which has a weight sufficient to counterbalance the cantilevered shield 100. It is preferred that each of the support stand legs 220 have wheels 235 mounted thereon for easy mobility of the entire assembly 10. The base 220 or wheels 235 may further contain locking or braking means to maintain the desired positioning of the assembly 200. Extending up from the base 220 is a support column 230 from which a cantilevered support arm 240 extends therefrom. The shield 100 is mounted upon the distal end of the support arm 240. A first end 242 of the support arm 240 is rotatably mounted upon the support column 230 for yaw adjustment of the arm 240 and the shield 100 thereon. The first end 242 of the support arm 240 is also disposed between a sliding sleeve 244 connected to a conventional pulley and counterweight system (not shown) which may be located within the interior of the hollow column 230. By rotating crank 246, the sliding sleeve 244 may be raised or lowered in order to adjust the vertical height of the support arm 240. Locking means 248 such as a retaining ring are provided in order to act as a safety stop to ensure the support arm 240 is secured in its desired vertical position should the pulley system fail. The support arm 240 further comprises a first linkage 250, a second linkage 252, and a third linkage 254. Although three linkages are shown and described, one or more linkages may be utilized. A ball and socket type joint 256 or other rotary joint connects the first linkage 250 and the second linkage 252 such that pitch, yaw and roll adjustments of the shield 100 are provided. The support arm 240 further comprises a pitch adjusting joint 258 connecting the second and third linkage 252,254, for adjusting the pitch or angle of the shield 100 with respect to the second linkage 252. Thus placement of the shield may be facilitated by the pitch, yaw and roll adjustments as well as the vertical height adjustment. The optional stand assembly 200 is not limited to the above description, as any counterweighted stand capable of pitch and vertical adjustments of a cantilevered arm may be utilized. It is preferred that the stand have wheels as well as yaw and roll adjustment capability of the shield 100. As shown in FIG. 2, the shield 100 may be mounted within a support structure 280 comprising a lower support plate 282 having sides 284 shaped to form a channel or frame for receiving the shield 100 therein. The support structure is preferably made of a strong material such as steel. The shield 100 and support frame 280 further comprise aligned holes (not shown) for receiving a steel rod 290 therein. The shield 100 and support frame 280 are rotatably mounted between the forked distal ends 255 of the third linkage 254 of the support arm 240 to further facilitate placement upon the patient. The threaded shanks of locking knobs 259 are inserted into aligned holes of the forked distal ends 255 and the shield 100 for locking the shield 100 into its desired rotary position. Preferably, the shield 100 is rotatably mounted about, or very close to, its center of gravity. Although the invention has been disclosed and described with respect to certain preferred embodiments, certain variations and modifications may occur to those skilled in the art upon reading this specification. For example other cross-sectional shapes of the shield could be utilized. Any such variations and modifications are within the purview of the invention notwithstanding the defining limitations of the accompanying claims and equivalents thereof.