Semi-automated custom capsule dispensing and assembly machine and method

An apparatus is used to dispense radiopharmaceuticals from a sealed source vial into capsules. The apparatus is particularly well suited for volatile radiopharmaceuticals such as radioiodine. This apparatus shields the operator from the radiopharmaceutical and also allows use of highly concentrated stock solutions.

FIELD OF THE INVENTION

In the field of nuclear medicine, radiopharmaceuticals are commonly prescribed for both diagnostic and therapeutic purposes. Most radiopharmaceuticals are dispensed into unit dose syringes under sterile conditions. Some radiopharmaceuticals, such as radioiodine (I-131 or I-123) are also dispensed in capsules so that they can be easily taken orally by the patient. The present invention is an apparatus and method to safely and accurately dispense liquid radiopharmaceuticals from a sealed vial into a capsule.

DESCRIPTION OF RELATED ART

Radiopharmaceuticals are commonly packaged in glass source vials sealed with a rubber septum and metal band. Radioiodine is often sold in source vials having a concentration of about 1,000 mCi/mL. In order to reduce radiation exposure during transportation and dispensing, these glass source vials are typically placed in a lead container which is referred in the industry as a pig. Radiopharmacies located across the country often keep several pigs on hand each containing a different radiopharmaceutical. When a prescription is received at a radiopharmacy, an aliquot of the radiopharmaceutical will be dispensed from the sealed glass source vial in the pig to a unit dose syringe or one or more capsules for administration to a patient.

In the past, some radiopharmaceuticals have been dispensed from a sealed source vial into capsules by hand using a syringe. Typically the dose is dispensed by hand into a single capsule. An operator grasps the lead pig housing a glass source vial containing a radiopharmaceutical in one hand and grasps a syringe with a needle in the other hand. The pig may have an opening or port above the rubber septum of the source vial. The operator inserts the needle through the port in the pig, punctures the rubber septum with the needle and withdraws an aliquot of the radiopharmaceutical into the syringe. The proximity of the hands to the radiopharmaceutical, especially in high concentrations, results in a rapid radiation exposure to the extremities of the operator. After transfer to the syringe, the activity level of the radiopharmaceutical in the syringe is measured using a dose calibrator. Corrections may be made for radioactive decay. An aliquot of the radiopharmaceutical is transferred from the syringe to one or more capsule bottoms filled with an excipient. A capsule top is placed on each capsule bottom and the completed capsules are placed in a transportation pig(s) for delivery to a hospital. At the medical facility, the capsules containing the radiopharmaceutical are orally administered to the patient for therapeutic or diagnostic purposes.

This manual prior art dispensing process is time consuming and subjects the operator to high extremity exposure rates from the radiopharmaceutical. There is a need for a better method and apparatus to dispense radiopharmaceuticals to reduce extremity exposure to occupational workers.

As an alternative to dispensing radioiodine by hand, some manufactures prefill capsules that are delivered to a medical facility or a radiopharmacy. These prefilled capsules are kept on hand until a need arises. This often requires use of larger and often multiple capsules to dispense the prescribed dose. It is common to require 2 or 3 prefilled capsules to deliver a single dose. Some patients do not tolerate multiple capsules or the increased amount of excipient caused by several capsules. So there is a dilemma. Prefilled capsules reduce extremity exposure but often require several capsules to deliver a dose. Manual filing of a single capsule with a stork solution having a high concentration (1,000 mCi/mL) results in extremity exposure to the radiopharmacist. There is a need for a method and apparatus that will allow dispensing into a single capsule and reduce extremity exposure to the radiopharmacist.

One attempt to solve the aforementioned difficulties is disclosed in International Application Number PCT/US02/32812, now publication number WO03/034444 entitled “Radiopharmaceutical Capsule Dispensing System” assigned to Mallinckrodt Inc., the assignee of the present invention. Unfortunately, the apparatus disclosed in the aforementioned publication was difficult to operate and sometimes resulted in more wasted product than anticipated. There is still a need for an apparatus and method that can prevent the escape of vapors from a source vial of a volatile radiopharmaceutical and provide safety and accuracy during the dispensing process.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for accurate dispensing of radiopharmaceuticals, including but not limited to highly volatile compounds such as radioiodine, from a sealed source vial into capsules which reduces extremity exposure to occupational workers and facilitates use of stock solutions with high concentrations. This capsule dispensing system is contained in a portable housing weighing less than 400 pounds.

The present invention allows dispensing of stock solutions of radioiodine having a concentration of 1,000 mCi/mL or more into a single capsule per dose. If properly used, this invention may reduce extremity exposure to a radiopharmacist by about 90% or more as compared to conventional manual filling techniques with a stock solution of 1,000 mCi/mL.

When a prescription for a radiopharmaceutical is received, a pump transfers a calculated volume of the radiopharmaceutical in accordance with this prescription from the sealed source vial into the capsule bottom. (The calculation accounts for a radioactive decay correction.) The capsule top is placed on the capsule bottom and the completed capsule is placed in a transportation pig. The top is screwed on the transportation pig and the completed capsule is ready for shipment to a medical facility for oral administration to a patient.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1,2and25, the semi-automated custom capsule dispensing system is generally identified by the numeral30and will hereinafter be referred to as the “Dispensing System30”. The Dispensing System30includes an input device32. The input device can be any number of different devices including, but not limited to a key pad as shown, or a key board or touch screen not shown, or any number of other input devices well known to those skilled in the art. The input device may also include a display device33. The display device can be any number of different devices including, but not limited to a liquid crystal display as shown, or a monitor or plasma screen or any number of other display devices well known to those skilled in the art. Conductors run from the input device32through the housing34as better seen inFIG. 23. The conductors from the input device are connected to an actuator85that controls the pump84. Conductors run from the actuator through the housing34to a power source, not shown. Conventional 110 v, 60 Hz, power can be used to operate the Dispensing System30.

The Dispensing System30includes a housing34with a top wall36, bottom wall38, left side wall40, right side wall42, back wall44and front wall46, which in this case is a door. The door46is connected the left side wall40with hinges48and to the right side wall42with a latch47. A handle50is connected to the top wall36. The housing defines an outer surface52and an inner surface54. Shielding materials56, such as lead is located between the outer surface52and the inner surface54. The purpose of the shielding materials is to reduce the amount of radiation exposure to an operator from the radiopharmaceutical. Other shielding materials may also be suitable for this application.

The shielding materials define a chamber58inside the housing. Interior components of the Dispensing System30are located inside the chamber58of the housing. Exterior components of the Dispensing System30are located outside the housing. The exterior components include the toggle assembly, generally identified by the numeral64, the delivery needle assembly, generally identified by the numeral66and the assembly system, generally identified by the numeral68. The assembly system includes the slide subassembly132and the capsule stop subassembly150, better seen in subsequent figures. A shelf67is attached to the door46and is used to mount or partially secure the toggle assembly, the delivery needle assembly and the assembly system. A removable upper capsule insert70and a removable bottom capsule insert72are placed in the assembly system68. A capsule bottom74is placed in the removable capsule bottom insert and a capsule cap76is placed in the removable bottom capsule insert. (The capsule bottom, which contains a suitable excipient and the capsule cap, which does not contain excipient are better seen inFIGS. 14-16.) The purpose of the Dispensing System30is dispense a unit dose of a liquid radiopharmaceutical into the capsule bottom and to assemble the capsule bottom and capsule cap into a completed capsule78for administration to a patient, while reducing the radiation exposure to the operator. (The completed capsule is better seen inFIGS. 17 and 18.)

The interior components include an interior mounting plate79, a pick-up needle assembly80, a safe82, a pump84, which includes an actuator85and conductors86. A suitable pump is the model millGAT produced by Global FIA, Inc of Fox Island, Wash. although other pumps may also be suitable in this application. A suitable actuator85is the model CP-DSM produced by Valco Instruments Co., Inc. InFIG. 2, the door46is shown in the open position to better reveal the interior components and the chamber58. During operation of the Dispensing System30, the door46is open only when the radiopharmaceutical is being replenished as better seen in the next figure. During day to day operation of the Dispensing System, the door46is closed and the interior components are positioned inside the chamber58to reduce radiation exposure from the radiopharmaceutical to the operator.

FIG. 3is an elevation view of the interior components of the Dispensing System with the pick-up needle assembly80in the clear position and a source vial88of radiopharmaceutical90above the safe82. The source vial88is shown in a position above the safe82. The source vial is in this position when it is inserted or removed from the safe. The source vial has a rubber septum92and a metal band94, which contain the radiopharmaceutical in the source vial. Containment is important with volatile radiopharmaceuticals like radioiodine. The present Dispensing System keeps the radiopharmaceutical sealed in the source vial, thus preventing radioactive fumes from escaping. This feature distinguishes the present invention from some prior art systems that required elaborate filtering systems to contain radioactive fumes from volatile radiopharmaceuticals.

The pick-up needle assembly80includes a pick-up needle96, a pick-up needle arm98, a sleeve100, a pick-up needle assembly guide rod and a pick-up needle assembly handle104. The pick-up needle assembly and the pick-up needle move from an clear position shown inFIG. 3to an inserted position shown inFIG. 2. The sleeve rides up and down the pick-up needle guide rod from the upper position the lower position. As the sleeve rides up and down, the arm and the needle are carried from the clear to the inserted position. While moving from the clear position to the inserted position, the pick-up needle96penetrates the rubber septum92and makes contact with the radiopharmaceutical in the bottom of the source vial88. In one embodiment, not shown, the pick-up needle has inlet holes on the side, not the end, like a conventional needle. Uptake of the radiopharmaceutical through a conventional needle could be obstructed by contact with the bottom of the source vial.

The pick-up needle assembly and the pick-up needle also move from a clear position shown inFIG. 3to an inserted position shown inFIG. 2. These positions enable the source vial of radiopharmaceutical to be inserted into the safe and be replaced as needed. In order to insert a source vial into the safe, the pick-up assembly and pick-up needle are moved to the upper clear position as shown inFIG. 3. The lid of the safe, not shown, is removed. A fresh source vial of radiopharmaceutical is inserted in the safe and the safe top is replaced on the safe. The operator grasps the finger104and rotates the sleeve100, the pick-up needle arm98and the pick-up needle from the clear to the engage position and from the upper to the lower position. While moving from the clear to the inserted position, the pick-up needle penetrates the rubber septum and comes into contact with the radiopharmaceutical in the source vial. The pick-up needle assembly and the pick-up needle are shown in the lower engaged position inFIG. 2.

To replace the source vial, the process is reversed. The pick-up needle assembly and the pick-up needle are moved from the lower to the upper position, withdrawing the needle from the rubber septum in the source vial. The pick-up needle assembly and the pick-up needle are then moved from the inserted to the clear position as shown inFIG. 3. The lid of the safe if taken off the safe and the old source vial is removed. A fresh source vial is put in the safe and the process is repeated. In many radiopharmacies, source vial replacement only occurs once per week.

A first conduit106connects the pick-up needle96with the pump84. A second conduit108connects the pump with the delivery needle110better seen inFIGS. 11-13. The radiopharmaceutical90flows from the source vial88, through the first conduit106, to the pump84, through the second conduit108to the delivery needle110and into the capsule bottom74, also better seen inFIGS. 11-13.

FIG. 4is an elevation view of the Dispensing System30with the exterior components in the start position. The toggle assembly64includes a toggle frame112, a toggle arm114, a guide frame116, a spring stop117, a spring118, a connecting rod120, a pivot arm122and a pivot arm handle124. The spring118surrounds the rod120and is captured between the guide frame116and the spring stop117, mounted on the rod120. The removable bottom capsule insert72, is carried by the pivot arm122, the purpose of the toggle assembly is to move the bottom capsule insert and the pivot arm from a lower position shown inFIG. 4to the upper position shown inFIG. 6. This movement for the lower to the upper position and back is accomplished by actuation of the toggle arm114which is pivot mounted in the toggle frame112. Moving the toggle arm carries the connecting rod and the pivot arm from the lower to the upper position and back. The pivot arm handle124is grasped by the operator to move the pivot arm122from the start (6:00) position, to the dispense (9:00) position, and then to the assemble (3:00) position.

The pivot arm can be rotated by the pivot arm handle124from the start position shown inFIG. 4to the dispense position shown inFIG. 5to the assemble position shown inFIG. 7.FIGS. 4-10portray the operational sequence of the Dispensing System30for dispensing a dose126of radiopharmaceutical and assembly of a completed capsule78, best seen inFIG. 18. Each step of the sequence will be described below.

InFIG. 4, the pivot arm122(which is a component of the assembly system68) is in the start or 6:00 position with the pivot arm handle pointing towards the operator. Because different sizes of capsules can be used, the Dispensing System has a set128, not shown, of removable upper capsule inserts and a set130, not shown, of removable bottom capsule inserts in different sizes to accommodate the different sizes of capsule. After reviewing the prescription for a unit dose, the operator decides on the size and number of capsule(s) needed and selects an appropriate upper capsule inset and an complementary sized bottom capsule insert from the sets128and130. For purposes of this example a medium sized capsule has been selected for assembly. The bottom capsule insert is placed in the pivot arm and the upper capsule insert in placed in the assembly system. A capsule bottom74is placed in the removable bottom capsule insert which is carried by the pivot arm, and a capsule cap76is placed in the removable upper capsule insert in the assembly system. The toggle assembly is in the lower position. For illustrative purposes, the claw154is shown separated from the removable upper capsule insert70inFIGS. 4-6; however in actuality the claw154contacts the removable upper capsule insert70as better seen inFIGS. 14-16. The function to the claw and the upper capsule insert will be discussed in greater detail below.

FIG. 5is an elevation view of the Dispensing System30ofFIG. 4except the pivot arm in now the fill position (9:00) under the delivery needle assembly66. The toggle assembly in still in the lower position as shown in the preceding figure. The relative position of the capsule bottom and the delivery needle110are better seen inFIG. 11. The assembly system68includes a slide subassembly132and a capsule stop subassembly150.

The slide subassembly132includes a slide guide rod134, a slide handle136, a slide arm138, a slide assembly/ejection rod140, and a plurality of height assembly slide stops,141,142and143rotateably mounted on a carousel145. A set144, not shown, of different sized removable slide stops allows the operator to select the appropriate size for the capsule being assembled.

The operator should rotate the carousel145to the proper location depending upon the capsule size to be used. Capsules come in various sizes including: 000, 00, 0, 1, 2, 3, 4, and 5. For smaller capsules (like a number 5), the tallest height assembly slide stop,141will be used. For medium sized capsules, the medium height assembly slide stop142will be used. (A medium sized capsule (number 3) is being assembled in this example.) For larger sized capsules (000), the small height assembly slide stop143will be used. The height assembly slide stop pins,141,142and143prevent the slide subassembly132from being extended upward which could crush the capsule. The height assembly slide stops permit the user to repeatably and reliably assembly the capsule cap and the capsule bottom to the proper depth depending on the size of the capsule being used.

The capsule stop subassembly is also a part of the assembly system68. The capsule stop subassembly has three positions (tool change out, closed position and open position) better seen ifFIGS. 19-21. InFIGS. 4 and 21, the capsule stop subassembly is in the tool change out position so an appropriately sized removable upper capsule inset can be placed in the tooling. InFIG. 5andFIG. 19, the capsule stop subassembly is in the closed position to hold the capsule cap76and the removable upper capsule insert in the tooling during assembly of the capsule. InFIG. 10andFIG. 20, the capsule stop subassembly is the open position to allow the completed capsule78to be ejected from the Dispensing System30.

FIG. 6is an elevation view of the Dispensing System30ofFIG. 4with the pivot arm122in the fill position underneath the delivery needle assembly66. The toggle arm has been actuated moving the toggle assembly64from the lower position ofFIG. 5to the upper position as shown inFIG. 6. This moves the capsule bottom closer to the delivery needle110, as better seen inFIG. 12. The position of the assembly system68, the slide subassembly132and the capsule stop subassembly150have not changed fromFIG. 5toFIG. 6.

The operator inputs into the input device32, shown inFIG. 1, the volume of liquid radiopharmaceutical to be dispensed. The desired volume to be dispensed from the source vial88onto the capsule excipient146in the capsule bottom74is calculated based upon the quantity of activity requested by the physician's prescription order and the radioiodine source strength at the time the capsule is made. The operator actuates the input device32to dispense the dose and signals are sent from the input device32to the actuator85, shown inFIGS. 2 and 3. The pump84then pumps the dose of liquid radiopharmaceutical from the source vial88through the delivery needle into the excipient in the capsule bottom held in the removable bottom capsule insert which is carried by the pivot arm.

A droplet of liquid radiopharmaceutical will sometimes hang on the tip111of the delivery needle110after the pump has been actuated to dispense the dose of radiopharmaceutical. To ensure that the lingering droplet of liquid radiopharmaceutical falls in the capsule bottom a push pin148is positioned in the delivery needle assembly66to deflect the delivery needle110causing the lingering droplet to move into the capsule bottom, as shown in greater detail inFIGS. 11-13. After the pump has dispensed the dose, the push pin is pressed inward (one to several times) in order to deflect the needle so that it touches the capsule wall as shown inFIG. 13. This motion is needed in order to remove the last droplet from the delivery needle110. Thereafter, the toggle arm114of the toggle assembly64is moved to the lower position as previously shown inFIG. 4, lowering the pivot arm122. The operator then grasps the pivot arm finger and moves the pivot arm to the assemble (3:00) position as shown inFIG. 7.

FIG. 7is an elevation view of the Dispensing System30ofFIG. 4with the pivot arm122in the assemble or 3:00 position, and the toggle assembly64in the lower position. The capsule stop subassembly150is in the closed position. The capsule stop subassembly150, better seen in section inFIGS. 22-24, includes a capsule stop subassembly handle152, a claw154, a u-shaped recess156in the claw, a slide stop rod162, a position pin160, a position pin spring161, an upper bushing164, a lower bushing166, and a sleeve168. The capsule stop subassembly handle is rotatably mounted on the slide rod135. The capsule stop subassembly handle152and the claw154are integrally connected and move in tandem.

The capsule stop subassembly handle152and the claw can be moved by the operator to three different positions better seen inFIGS. 19-21. The first position, as shown inFIGS. 7 and 19is referred to as the closed position and is also shown inFIGS. 14-16. In the closed position, the claw154contacts the capsule cap and holds it in place during the assembly process. The second position of the capsule stop subassembly handle152and the integral claw is referred to as the open position and is the position shown inFIG. 10andFIGS. 17-18. In the open position, the u-shaped recess156in the claw154is clear of the capsule cap and the completed capsule may be ejected from the assembly system. The third position of the capsule stop subassembly handle152and the integral claw is referred to as the tool change out position, better seen inFIG. 21. In the tool change out position, the operator can remove and replace the removable upper capsule insert to accommodate capsule caps of different sizes. This is also the position where the operator inserts the capsule cap into the removable upper capsule insert. Before moving to the next step, the operator moves the toggle arm114to the upper position as shown in the next figure.

FIG. 8is an elevation view of the Dispensing System30ofFIG. 4with the pivot arm in the assemble (3:00) position, and the toggle assembly64in the upper position. The capsule stop subassembly handle152and the integral claw are in the closed position as shown inFIG. 19to hold the capsule cap in the removable upper capsule insert during the assembly process which will be described in the following figures.

FIG. 9is an elevation view of the Dispensing System30ofFIG. 8with the assembly slide136in the upper position. The assembly/eject rod is moved upward as the assembly slide136is moved upward to complete the assembly of the capsule cap and the capsule bottom as better seen in section view inFIG. 16. A removable height assembly stop142engages the slide stop rod162to prevent crushing of the capsule cap and the capsule bottom. The height of the removable height assembly stop is selected to complement the size of the capsule for a particular dose. Several other removable height assembly stops of different heights,141and143are positioned on a rotating carousel145, to facilitate reconfiguration of the Dispensing System30, when different sized capsules are required. The Dispensing System comes with a set144, not shown of removable height stops to facilitate production of capsules of different sizes. After the completed capsule78has been assembled, the slide assembly is returned to the lower position.

FIG. 10is an elevation view of the Dispensing System30ofFIG. 8. In order to eject the completed capsule78, the capsule stop subassembly handle152and the integral claw must be moved to the open position, better seen inFIG. 20. In the open position, the u-shaped recess of the claw is positioned above the completed capsule. Then, the slide assembly is moved to the upper position as shown inFIG. 10to eject the completed capsule78through the u-shaped recess of the claw. A section view of the ejection of the completed capsule is shown inFIG. 18.

FIGS. 11-13are section views of the delivery needle assembly66including the cowling assembly170which includes the upper portion of the cowling172and the lower portion174which sit on the shelf67. In order to reduce exposure to operator, certain parts of the Delivery System30can be formed of tungsten instead of lead. Tungsten has better shielding properties than lead. The following components can be fabricated from tungsten: the upper portion of the cowling172, the lower portion of the cowling174, the source vial safe,82and the source vial lid, the push pin148, the pivot arm122, the removable upper capsule insert70, the removable lower capsule insert72and the jig186.

FIG. 11shows the pivot arm122, the removable lower capsule insert72and the capsule bottom74below the delivery needle assembly66in the same position asFIG. 5. InFIG. 11andFIG. 5, the toggle assembly64is in the lower position.FIG. 12shows the toggle assembly64in the upper position as seen inFIG. 6. The radiopharmaceutical is dispensed into the capsule bottom74inFIG. 12.FIG. 13shows the toggle assembly64in the upper position as seen inFIG. 6. InFIG. 13, the push pin148is pushed inward to deflect the delivery needle110into contact with the capsule bottom, as shown. The contact with the capsule bottom causes the last droplet of radiopharmaceutical to move into the capsule bottom, thus completing the dispensing of the radiopharmaceutical.

FIGS. 14-18are section views of the assembly and ejection process of the capsule.FIG. 14is a section view of the components shown inFIG. 5. The capsule cap76is positioned above the capsule bottom74and the toggle assembly64is in the lower position.FIG. 15is a section view of the components shown inFIG. 6. The toggle assembly64has been shifted to the upper position.FIG. 16is a section view of the components shown inFIG. 9. The assembly/eject rod140has been raised to assemble the capsule cap and the capsule bottom.FIG. 16is a section view of the claw and adjustable hold down pin in the open position.FIG. 17is a section view of the components shown inFIG. 10. In this view, the completed capsule78is ejected from the Dispensing System30.

FIGS. 19-21are plan views of the capsule stop subassembly150including the claw154and the capsule stop subassembly handle152. InFIG. 19, the capsule stop subassembly is in the closed position holding the capsule cap in the removable upper capsule insert as better seen in section view inFIG. 14. InFIG. 20, the capsule stop subassembly is in the open position allowing the completed capsule to be ejected from the Dispensing System as better seen in section view inFIG. 18. InFIG. 21, the capsule stop subassembly is in the tool change out position allowing the removable upper capsule insert to be removed from the jig so another insert of a different size can be placed in the jig.

FIG. 22is a section view along the line22-22ofFIG. 19of the assembly system68. The assembly system includes the slide subassembly and the capsule stop subassembly150. The capsule stop subassembly is best seen in plan view inFIGS. 19-21. The slide subassembly is better seen inFIGS. 22-24as the subassembly moves through the various assembly steps. InFIG. 22, the slide arm138is in the lower position as shown inFIG. 7. The assembly/eject rod140, better seen inFIG. 15is likewise in the lower position. InFIG. 23, the slide arm is in the assemble position as better seen inFIG. 9. The assembly/ejection rod140, better seen inFIG. 16is also in the upper assemble position. InFIG. 24, the slide arm138is in the eject position as shown inFIG. 10. The assembly/eject rod140, better seen inFIG. 18is also in the eject position.

InFIG. 22, a screw158connects slide handle136to slide rod135which converts to slide arm138. An upper bushing164and a lower bushing166are pressed fit into a sleeve168. The sleeve is pressed to fit in a bore in the handle152.

A position pin spring160is held in place in the handle152by a spring retainer190. The spring retainer threadibly engages the capsule stop subassembly handle152. The spring161surrounds a portion of the position pin160. A spring stop192is mounted on the position pin160. The spring161is captured between the spring retainer190and the spring stop192. This arrangement gives the position pin160the ability to engage and disengage recesses in the shelf67as the capsule stop assembly handle152moves from the position ofFIG. 19, to the other positions shown inFIGS. 20 and 21.

FIG. 23is a section view along the line22-22ofFIG. 19. The slide handle136and the slide arm138are in the upper assemble position as shown inFIG. 9. The assembly/eject rod140is in the upper assemble position as best seen inFIG. 16.

FIG. 24is a section view along the line24-24ofFIG. 20. In this view, the slide handle136and the slide arm138are in the upper eject position as shown inFIG. 10. The assembly/eject rod140is likewise in the upper eject position as best seen inFIG. 18.

FIG. 25is a perspective of the pathway of the conductors86through the housing34. In order shield operators, a z-shaped pathway87is formed in the shielding materials56and the back wall36. The conductors86are placed in this z-shaped pathway.