## 1 Introduction  
Pancreatic ductal adenocarcinoma (PDA), also known as pancreatic cancer, is projected to become the second leading cause of cancer-related mortality by 2030 [1]. Despite modest advances in conventional systemic therapies, the 5-year overall survival (OS) for PDAC remains a dismal 11% [2], in part because of its advanced stage at presentation precluding curative-intent resection and a high propensity for recurrence [3]. Early-stage pancreatic cancer usually has no symptoms. When symptoms do occur, the tumor has usually spread to surrounding tissues or distant organs [4]. Most patients are inoperable at the time of diagnosis due to locally advanced disease or metastasis and experience severe abdominal pain as the disease progresses. Therefore, the treatment of patients with advanced pancreatic cancer is palliative, with the main goal of prolonging the life of patients and alleviating their pain. Many studies have shown that focused ultrasound has become a modality for the palliative treatment of pancreatic tumors. There is now a general consensus that a temperature above 55 \({}^{\circ}\)C maintained for more than 1 s induces nonreversible enzymatic denaturation and leads to coagulative necrosis and cell death [5, 6]. The absorption of acoustic energy by biological tissues can lead to a rapid increase in the temperature of the target area. High-intensity focused ultrasound (HIFU) aims to achieve this temperature threshold in the target area, induce coagulative necrosis, and ablate the tumor without affecting the surrounding healthy tissue. HIFU systems usually use 'high-intensity' mode with the intensity at the focus exceeding 1000 W/cm\({}^{2}\). Cavitation, boiling, and strong nonlinear acoustic emissions can be detected in this mode, which can complicate mathematical models of the focal domain and cannot accurately predict the temperature rise and the shape of coagulative necrosis [7]. In numerous studies, HIFU has been shown to be safe, effective, and practicable, but there are a few HIFU-related adverse effects [8; 9]. In a study published by [PERSON] et al., ultrasound with a frequency of 0.8 MHz, acoustic power of 200-400 W, and a duration of more than 50 s for a single target was used to achieve palliative treatment of pancreatic cancer. Transient subcutaneous edema of the proximal upper abdominal wall was observed in nine of fifteen patients. In one patient there was superficial skin burning in the region of the navel (degree IIa) [10]. [PERSON] et al. used focused ultrasound in the palliative treatment of pancreatic cancer with a center frequency of 0.8 MHz or 1.6 MHz and an acoustic power of 140 W-240 W; the duration of exposure depended on the monitoring of US. In forty-nine treatments, twenty-eight patients had minor complications, such as mild and severe abdominal pain with vomiting, and five patients had major complications, such as skin burn (II, III) and pancreaticoduodenal fistula [11]. During HIFU treatment, the patient's discomfort increased proportionally with increasing delivered energy [12], and pain levels seemed to be independent of the dose of anesthetic or sedation [13]. Some patients interrupted their treatment due to pain [12; 13; 14]. Even though most of the studies were performed with US-guided HIFU, standardization of energy, power, and technical parameters are lacking, and are still needed to obtain the best results at the minimum risk for the patient. Radiofrequency ablation (RFA) and irreversible electroporation (IRE) can provide palliative treatment for pancreatic cancer patients in a minimally invasive manner, but they are also limited by complications, and they should be adopted only by expert users in specialized centers of interactive pancreatology [15]. The application of moderate-intensity focused ultrasound (MIFU) in the treatment of advanced pancreatic cancer proposed in this paper is non-invasive and helps to avoid these complications. In addition to HIFU, MIFU also plays an important role in clinical treatment.