Introduction: Immobilization Devices for Radiation Therapy: Local Production

Radiation therapy is a common component of cancer treatment that employs high energy radiation to target and destroy cancer tissue. Patient positioning and stability are paramount to a safe and efficacious procedure. Thus, the treatment of breast and thoracic cancers is typically accompanied by a specialized breast board that serves to immobilize the patient during the process. However, commercial immobilization devices are prohibitively expensive and/or suffer from availability constraints for medical sites in the developing world [1].

The aim of this project is to improve upon a radiation therapy immobilization device capable of maintaining patients in a fixed position and lifting the torso at a set of desired angles. The materials must be reusable, cost effective, minimally attenuative of the beam used in radiation therapy, and readily available in the developing world. This device will be specifically designed for an external radiation therapy clinic in Mwanza, Tanzania, but the methods developed here may be applicable to other regions. For this semester, the specific goals are: 1) to add a method of hand immobilization using sets of removable handles above the patient’s head level, 2) to add sites for wing block attachment to serve as patient armrests, 3) to recess/reduce the protrusion of the hinges connecting the baseboard to the chest board for patient comfort, all the while ensuring local producibility of the device.

Hand immobilization will be achieved using a twisted nylon rope that can be positioned using knots to anchor the rope in various sets of holes above the patient’s head level, corresponding to the appropriate dimensions of the patient. An important specification to consider will be the stability of the handles, which we intend to test by applying force on top of the handles parallel to the plane of the board to simulate patient attachment. We predict that the handle will be able to withstand the normal pulling/grip strength of a patient. To accompany the hand restraints, the areas on the board flanking the patient's arm will be modified to allow for the attachment of wing blocks to serve as armrests. The next goal is to reduce the protrusion of hinges from the region connecting the base board to the chest board, which we intend to accomplish using a fabric hinge, and measuring the outcome by the reduction in protrusion length in mm. Based on the physical dimensions of the existing design, we predict that a reduction of 5mm or more is feasible. Finally, we will ensure the local producibility of the design by contacting individuals, businesses, or organizations in the region.

Step 1: Materials & Tools

Materials:

1 Pine 2x12x12

1 Pine 4x4x8

1 Pine 1x4x12

1 Circular Pine Fence Post

1 1in diameter x 18in long dowel rod

~10oz of wood glue

Phillips screws with washers

Latex Paint/Primer

Heavy Nylon Webbing (~1 yard)

Epoxy

Twisted Nylon Rope (10 ft)

Tools:

Chop saw

Band saw

Jig saw

Milling Machine

Jig Saw

Drill

Screw Driver

Lighter

Paint Brush

Table saw

Step 2: Cuts

Refer to the CAD drawings for measurements and relative locations of cuts.

2x12x12

Using the table saw (or a hand saw), cut the 2x12x12 into the following pieces:

Two 42" length pieces

Two 21.5" length pieces

Using the jig saw, cut a rounded hole out of the edge of each 21.5" piece as shown in Figure 2. The hole should be 3.5" wide at the base, 3" tall, and begin 2" from the bottom of the board. These will be used to form the main body of the board, divided into the upper and lower sections. Alternatively, the cut could be made with a handsaw but will require more time and effort.

4x4x6

Using the chop saw, cut the 4x4x6 into the following pieces:

  • Two pieces that are 9.74" tall on the back end and 10.87" tall on the front end. Use the chop saw at an angle of 15 degrees for the first cut and then 0 degrees for the second cut so that the length and angle are exactly the same for both blocks.
  • Two pieces that are 6.58" tall on the back end and 7.29" tall on the front end. Use the chop saw at angle of 10 degrees for the first cut and then 0 degrees for the second cut so that the length and angle are exactly the same for both blocks. Two pieces that are 3.31" tall on the back end and 3.66" tall on the front end. Use the chop saw at angle of 5 degrees for the first cut and then 0 degrees for the second cut so that the length and angle are exactly the same for both blocks. These pieces will form the angled blocks that hold the breast board up at an angle.
  • Three rectangular pieces that are 10” tall.
    • Use a bandsaw to cut one of these pieces along its diagonals on its smaller faces to form two triangular prisms. Drill the holes as described in Step 2 first before cutting for an easier time.
  • Alternatively, this can be done with a handsaw but is very unlikely to be the desired straight, smooth cut

1x4x10

Using the table saw (or a handsaw), cut the 1x4x10 into the following pieces:

  • Three 22" length pieces (or whatever twice the width of the 2x12x12 board is - it may not be exact) These pieces will be used as the supports across the back of the main boards.

Dowel Rod

Using the chop saw, cut the dowel rod into the following pieces:

  • Twenty-two 2" length pieces. These will be used as the pegs that attach the angle blocks and butt stop to the board.

Pine Fence Post

Using the chop saw, cut the pine fence post into the following pieces:

  • One piece 22" in length (or whatever twice the width of the 2x12x12 board is - it may not be exact) Then, using the band saw the pine fence post in half lengthwise. This should result in two pieces 22" in length with a semicircular cross section.

Step 3: Notching & Drilling

Refer to the final CAD drawings for locations and dimensions of notches and holes.

Notching

The notches will be used as a space to hold the 1x4 planks that go across the back of the 2x12 boards as supports.

Using the mill, make notches that span the entire width of the board, about 3.5" tall (or whatever the exact width of the 1x4 is), and about 3/4" deep (or whatever the exact thickness of the 1x4 is) by covering the entire area with at about 1/10" of depth at a time. Alternatively, you can raise the blade on a table saw the correct thickness and go 1/8 in of length at a time down the width. Make notches at the following locations:

  • 10" from one end of both 42" 2x12s boards. Make sure the notches line up across both boards when placed side by side so that the 1x4 support will fit when the boards are glued together.
  • 7 1/2" from the other end of both 42" 2x12 boards. Make sure the notches line up across both boards when placed side by side so that the 1x4 support will fit when the boards are glued together.
  • 9" from one end of both 21.5" 2x12 boards. Make sure the notches line up across both boards when placed side by side so that the 1x4 support will fit when the boards are glued together.
  • If a mill machine is unavailable, the notch can be created using a chisel.

Drilling Holes

  • Drill holes that are 1" deep and 1" in diameter with centers in the locations shown in the images above on the 2x12 boards. For the bottom board, extend the holes horizontally ¼ “ to allow easier fitting of the buttstop. For the top board, extend the hole closest to the semi-circular cut by ¼” as well as shown in the drawings above.
  • The 4 holes for the rope on the front of the board should drilled all the way through the boards.
  • Drill holes that are 1" deep and 1" in diameter into the exact center of each of the angled 4x4 blocks.
  • Drill two holes that are 1" deep and 1" in diameter with centers 11" (or however far apart the holes in the center of the 2x12 boards are) in the flat side of the semicircular pine fence post. These holes should be exactly lined up with those in the board so that once the pegs are glued into the butt stop, they will fit in the holes on the board.
  • Drill two 1” of holes on one of the larger faces of all three of the 10” blocks, where their centers are separated by 8” as shown in the images above. Repeat this on the opposite side of each block. One of blocks can then be cut along the diagonals as described in Step 1.
  • Extend one of the holes about ¼ “ away from the other hole, only on one side of the other two blocks. If a drill press is unavailable, a hand drill may be used.
  • If a drill press is unavailable, a hand drill may be used.

Step 4: Gluing

Refer to the final CAD drawings for placement of pieces during gluing.

Top Boards:

  • Apply wood glue liberally to the inside edge of one of the top boards. This should be the edge of the board that does not have the semicircular section cut out.
  • Lay the board on a flat surface and push the corresponding edge of the other top board against the glue. Both semicircular cutouts should be on the outside edges of the glued together board.
  • Apply clamps so that the glued portion of the boards are held firmly together, without clamping so hard that the boards buckle and are no longer flat on the ground or other surface they are laying on.
  • Leave boards clamped for at least 8 hours, and allow the glue at least 24 hours total to dry before moving the boards.

Bottom Boards:

  • Apply wood glue liberally to the inside edge of one of the bottom boards. The inside edge of each board can be determined by looking at the back of the boards and lining up the holes drilled for the index, making sure that they are the correct width apart.
  • Lay the board on a flat surface and push the corresponding edge of the other bottom board against the glue.
  • Apply clamps so that the glued portion of the boards are held firmly together, without clamping so hard that the boards buckle and are no longer flat on the ground or other surface they are laying on.
  • Leave boards clamped for at least 8 hours, and allow the glue at least 24 hours total to dry before moving the boards.

Butt Stop:

  • Apply wood glue liberally to one end of each peg and place one in each hole drilled in the butt stop.
  • Clamp each peg into place. Leave pegs clamped for at least 8 hours, and allow the glue at least 24 hours total to dry before moving the butt stop.

Angle Blocks:

  • Apply wood glue liberally to one end of each peg and place each in its corresponding hole cut in the top of the blocks.
  • Clamp each peg into place. Leave pegs clamped for at least 8 hours, and allow the glue at least 24 hours total to dry before moving the butt stop.

Wing Blocks:

  • Apply wood glue liberally to one end of each peg and place one in each hole drilled in the wing blocks (the unextended holes for the rectangular pieces).
  • Clamp each peg into place. Leave pegs clamped for at least 8 hours, and allow the glue at least 24 hours total to dry before moving the butt stop.

Step 5: Epoxy

Refer to final CAD drawings for measurements and placement of holes.

  • Fill each hole drilled in the back of the bottom board in with epoxy and let the epoxy cure for 24 hours.
  • A 0.5" hole will need to be drilled into each well of epoxy. Mark the center of each hole so that the centers are square with the top of the board and exactly 9" apart.
  • Drill 0.5" holes in the epoxy, centered at the points marked in Step 2. begin by drilling a very small hole and gradually increase the size of the drill bit until reaching 0.5".Note: it is important that the holes be drilled as straight up and down as possible. Use a drill press if available. If not, a hand drill can be used.

Step 6: Paint and Assembly

Refer to image for placement of pieces during assembly.

  • Paint all components of the board: the top half, bottom half, butt stop, and angle blocks.Note: be careful not to paint dowels or holes so that they still fit together, or drill slightly larger holes to account for paint thickness.
  • Once paint has dried, write the corresponding angle (in degrees) on the back of each set of angle blocks.
  • Using a pair of pliers, cut a strip of the nylon hinge equivalent to the length of the edge of the boards that should be attached. Burn the edges of the hinge to prevent fraying.
  • Place the hinge along the edges and hand drill 6 screws about half an inch away from the top face of both the top board and the bottom board. The loose ends of the nylon strip should face the bottom end of the boards and can be restrained by drilling screws on the corners half an inch from the bottom of the boards.
  • Alternatively, this can be done with a screwdriver, but will require significant effort.
  • Burn around the holes created in the nylon hinge before screwing down completely to prevent fraying.
  • The orientation of the nylon hinge should be such that the board closes with the top faces of the top and bottom board coming together.
  • Mark the rope with a marker every six inches from one of its ends. When the knots are tied, these marks should lie flush with the board as seen from the top after the rope has been threaded.

Comments

author
DIY Hacks and How Tos (author)2017-04-25

Nice design. I remember radiation therapy being a real pain. It's good that you can find better ways to make it easier.