**3. Results**

#### *3.1. Prototype Design*

During the design of the Lung Tumor Movement Simulator (LTMS) (Figure 3), several mechanical designs were studied and proposed; in the end, a design composed of two sliders was chosen.

**Figure 3.** 3D model of the Lung Tumor Movement Simulator. Main design of the prototype *A* and eight tips model that were designed to give versatility to the model. Tips *D*–*H* were designed with the purpose of holding a nanoDot™radiation dosimeter. Tips *B*, *C* and *I* were designed to hold a test tube with contrast fluids for other purposes.

This design is formed by two stepper motors, which move the mechanical elements (Figure 2) to achieve the desired movement. There is an upper motor, which controls the upwards and downwards motion of the Tip that simulates the tumor position. Then, there is a lower motor which controls the of pushing forward and backward the Tip, which represents the targeted tumor. The entire prototype is composed of 15 different parts. Their dimensions and weights are shown in Table 1.

The biggest challenge during the design was how to achieve the synchronization of the two stepper motors in order to obtain an accurate path. This problem was overcome with the addition of two optical endstops. These endstops were placed underneath each stepper motor and a protuberance on each axis is what triggers the optic mechanism.

#### *3.2. Movement and Path Simulation*

To validate the prototype mechanism, it was necessary to evaluate the mobility of the whole system as shown in Figure 4. By using the feature of Movement Simulation from Unigraphics NX 11 (Siemens, Berlin, Germany), the Tip trajectory was simulated taking into account gravity, friction and speed limits.

During the virtual simulation, it was observed that the Tumor Movement Area, which is shown in Figure 4, was the expected area for the tumor movement cycle. Furthermore, the simulation was done with the same speed for the two stepper motors and one specific mechanical configuration; however, if the speed or the length of the mechanical transmission were modified, the height and width of the desired area would be modified.

**Figure 4.** Virtual simulation of the desired area to cover with the LTMS in order to validate the viability of the system design.
