# Risk Management for the Reliability of Robotic Assisted Treatment of Non-resectable Liver Tumors
## 2 Materials and Methods
### Identifying Risk Control Measures for the Treatment of Non-resectable HCC Tumors
**Therapeutic needle insertion:** The needle guiding module positions the needle on the defined trajectory (confirmed with possible minor corrections after tumor location with the I-US probe). The needle is then positioned on the desired trajectory above the patient's skin, but as close as possible to it. After the trajectory validation, the robot will remain in the current position and the needle will be inserted using the insertion module, monitoring in real time the resistive force to avoid needle deflection;
3. **Therapeutic needle insertion into the hepatic parenchyma:** The needle is inserted continuously up to the proximity of the hepatic parenchyma. When the needle touches it, the trajectory is once more validated and the needle insertion into the hepatic tissue is initiated. From this point on, the needle can be seen by means of the US probe that confirms reaching of the target point. * **Multiple needle insertion:** When the treatment requires the use of multiple needles, those are inserted by following Steps C.2 and C.3 until all the required therapeutic needles are inserted. The insertion order is established such that the I-US probe may be repositioned without affecting the already inserted needles. _Note:_ Since multiple needle insertions increase the risk of hepatoma, further research (in vivo) is intended to determine the maximum number of needles allowed. 4. **Delivery of the treatment:** After all needles are inserted, their position is confirmed by the medical personnel and the treatment is delivered. For brachytherapy treatment, the patient should be transferred to a controlled room specialized for brachytherapy treatment;
5. **Needle extraction and operating field check:** After completing the procedure, the needles are extracted either by the robot or manually (depending on the procedure). After extraction, the operating field is checked for eventual hemorrhages;
6. **Ultrasound probe extraction:** After validating the position of all needles, the US probe is retracted, followed by extracting the laparoscopic camera and suturing the incision points of the two trocars. The analysis of the possible hazards and their estimated occurrence, together with the procedure protocol, led to the definition of the main design constraints for the new robotic system which should be accounted for and implemented as risk control measures:  
1. The needle guiding module must operate with **high precision**, due to the fact that the robot must insert therapeutic needles within the tumors (a maximum error of 2 mm is accepted [3,4]);
2. The robot workspace should have no singularities (robot configurations where the mechanism is not well behaved, losing or gaining degrees of freedom). A singularity-free workspace may be achieved through mechanism design;
3. Since the medical procedure requires the manipulation of two medical tools (therapeutic needles and I-US) in a distinct manner, the robotic system must have two independent modules. The first module is designed to insert and manipulate the **US probe**, whereas the **second module** is designed to **insert the therapeutic needles**. The relative positioning of the two guiding modules is always known; therefore, while the clinician actively locates the tumor, the needle will also adjust its position such that the needle targets the tumor;
4. Because the procedure is to be minimally invasive, the **US probe guiding module** needs to work based on the **RCM concept:**
5.