The "Z" Box

Provision Center for Proton Therapy (Knoxville, Tennessee) uses Alpha Cradle (Smithers Medical Products Inc) because it provides an adaptive, reproducible, and solid immobilization device for proton therapy treatments of the thorax and abdominal areas. Unlike other devices that shrink and pull away from the patient, Alpha Cradle molds upward around the patient, allowing him or her to remain in a comfortable position. The device fills gaps and voids around the body to better immobilize the patient and allow for a more accurate treatment plan.

However, the Alpha Cradle can be difficult to work with as technologists navigate the positioning bag and the patient. Several hands are needed to assist in complex cases involving the thoracic and abdominal regions. In addition, many of these setups present a challenge for patients who are unable to hold both arms above their head.

A device was needed that would take the place of those extra hands. Some centers use Styrofoam boxes made individually for each patient that allow the Alpha Cradle to remain inside the box and grow around the patient, but they must be made new every time for every patient. The box’s strength often is insufficient when the patient climbs into it for computed tomography simulation.

The “Z” box expands on the Styrofoam box idea. Instead of having to make a new box every time, the “Z” box is stronger and can be used repeatedly. In addition, the “Z” box is fully adjustable to meet any arm position. The side “wings” of the board operate on a hinge and can be raised or lowered to the desired height to support the patient’s arms sufficiently. The adjustable extension under the hands and forearms can be locked in at the desired height (see Figure 1). These adjustments not only support the patient in a comfortable position but also create a deep mold for the Alpha Cradle. This deep mold provides an accurate casting around the patient’s arms. The reproducibility of the arm position is one of the most important factors in treatment alignment for proton therapy.


Figure 1. "Z" box made of medical-grade plastic demonstrating the adjustable wings under the arms.

An additional benefit is that a single therapist can create a quality bag. The Alpha Cradle bag is placed on top of the “Z” box, and the Alpha Cradle product is poured into the bag. A piece of Styrofoam insulation board can be used as a base for the mold as well as a makeshift pillow under the patient’s head. These pieces are placed inside of the plastic bag. As the Alpha Cradle spreads and expands, the material must rise upward around the patient rather than spilling over the edge because of the sturdy walls of the “Z” box. The adjustable wings under the arms create a bowl filled with the Alpha Cradle, which, similar to the sides, forces the foam to expand upward to form a cradle around the patient’s arms. Once hardened, the mold is removed from the “Z” box. The device is entirely self-supporting and has a special “Z” bar indexing system the same shape as the “Z” box so the contour of the bag fits within the bar and is held securely to the table (see Figure 2).


Figure 2. Completed mold made in "Z" Box representing the deep arm pockets and head support.

The “Z” box addresses this problem. Its abilities have been proven both in simulations through faster setups, as well as in the treatment room by setting up patients with few to no corrections on the table. The box can be used for immobilization of any thoracic or abdominal case, and can be rotated 180° and used to create a mold of the legs for pelvic simulations. It also offers a considerable advantage in mold creation for computed tomography simulation setups and treatment deliveries. Use of the “Z” box in the Provision Center for Proton Therapy’s clinical area continues to increase.

I built the first “Z” box out of wood in my garage. The current device is made of a medically acceptable plastic material that is lightweight, strong, durable, and enables easy and thorough cleaning. Although the “Z” box originally was designed for use in proton therapy and with Alpha Cradle products, it also can be used in conventional photon therapy with the same ease and results, as well as with other products available for immobilization. With some immobilization devices, several hands are needed to ensure the success of a patient mold.

Zachary Allen Dutton, R.T.(R)(T), 07.20.2016
Posted in proton, simulation, treatment, Z box