# Risk Management for the Reliability of Robotic Assisted Treatment of Non-resectable Liver Tumors
## 1 Introduction  
One of the most lethal forms of cancer in the world is hepatocellular carcinoma (HCC), which represents the most common primary malignant liver tumor. HCC represents more than 5% of all cancer localizations on a world scale, being the fifth most common malignant localization in males and the ninth in females [1]. The number of HCC deaths per year is almost equal to the incidence with 0.93/1 lethality index. The best curative options, involving the complete removal of the malignant cells from the body, are surgical resection of the tumor and liver transplant [2]. However, only 20% of patients with HCC can be subjected to one of these procedures due to various reasons related to the disease (localization, size, vascularization, number of tumors, spread) or patient (general state, other associated diseases, i.e., cirrhosis) [1]. When resection and liver transplant are not viable options, there are multiple locoregional treatments (curative or palliative ones) which have been investigated in medical centers all over the world, including TACE (trans-arterial chemoembolization), HDR (high-dosage radiation) brachytherapy, RFA (radiofrequency ablation), and delivery of chemotherapeutic drugs injected directly inside the tumor [3]. According to a team ofcondition), allowing them to become liver transplant candidates. With all the recent advancements in nuclear medicine and medicinal chemistry, these targeted approaches have a high potential to increase the patient survivability and quality of life, but they are hindered by a common constraint: the placement accuracy of the therapy delivery tool is critical, with a maximum acceptable positioning error of 2 mm which in most cases cannot be achieved manually [4]. According to [5] the combined positioning error, assuming 1\({}^{\circ}\) angular positioning error and 1 mm Cartesian positioning error from the zero compensation position (values that may be exceeded when the needle is inserted manually, leading to worse outcomes), of a needle inserted in the patient body (with zero needle deflection) is approximately 2.5 mm for 50 mm depth and approximately 5 mm at 200 mm depth. An efficient solution that can overcome the human limitations in such techniques is represented by the use of robotic systems which, based on careful preplanning of the procedure, enable tumor targeting with increased accuracy [6]. The most promising results have been achieved in the treatment of tumors located in the prostate [7], lung [8], or breast [9], but all studies reflected that the procedure difficulty increases as the tumors are located deeper in the body (as the access path is longer and needle orientation errors, especially, multiply) and is more complicated for organs with complex vascular structure. In fact, the therapeutic feasibility of HDR brachytherapy for HCC treatment is not yet proven, mostly due to the lack of accurate technical solutions capable of delivering the therapeutic agent in a reliable manner which facilitates patient safety and decreases the overall risk of the medical procedure. When considering the development of a technical solution designed to facilitate targeted treatment of HCC, besides accuracy, other characteristics should be considered which are strongly related to the patient safety. The technical solution (e.g., a robotic system) must comply with various technical and medical requirements (e.g., the robot must be able to properly manipulate the medical instruments with minimum risk of causing harm; some critical components must be sterilized and, therefore, modularity is required, etc.). The accuracy and patient safety, considering the robotic assisted medical procedure, should also be enhanced by using a real-time imaging technique. Since the proposed procedure is minimally invasive, a pneumoperitoneum is created beforehand, and most likely, the liver position will change (relative to the position defined preoperatively based on the volumetric data).