Electromagnetic tracking (ET) navigation software has been previously shown to reduce radiation dose, number of CT scans, and needle manipulations in biopsy patients. The purpose of our study is to evaluate the safety and efficacy of ET navigation software in patients undergoing microwave ablation of liver tumors. A single-center, retrospective review of all microwave ablations of liver tumors less than or equal to 3 cm in diameter from January 1, 2017 through June 30, 2109 was performed. Variables recorded include patient demographics, type of tumor, number of tumors ablated in a single session, number of CT scans (NCT), radiation dose (RD), tumor location, ± preablation iodized oil stain of target lesion (IOS), response rate (using mRECIST criteria), adverse events, procedure time (PT), and anesthesia time (AT). In total, 266 tumors were ablated in 196 patients, over 231 sessions; median age of patients is 66 years old, with 74.1% male. 90 tumors were ablated using ET and 156 were ablated without ET. The median RD for the ET patients was 656 mGycm, compared to 683 mGycm in the non-ET group (P = 0.05). Median NCT in the ET group was 5 and 6 in the non-ET group (P <0.01). ET patients with IOS tumors had lower RD and NCT compared to non-ET patients with IOS (P = 0.02, P <0.01 respectively) and non-ET patients without IOS in their tumors (P = 0.09, P = 0.01 respectively). For difficult to navigate dome lesions (tumors in segments 7 and 8 based Couinaud classification), ET patients had lower RD and NCT compared to non-ET patients (P = 0.1, P <0.01 respectively). PT between the ET and non-ET dome lesion groups was not significantly different in patients undergoing ablation of a single tumor (53 minutes versus 50 minutes, P = 0.27); similar findings were also noted for AT (2 hours and 7 minutes versus 2 hours and 3 minutes, P = 0.67). Complete response rate at 3 months was 98.2% in the ET group and 92.1% in the non-ET group (P = 0.04). ET can potentially reduce RD and NCT in microwave ablation patients, including in tumors with IOS or a dome lesion. PT and AT were comparable between the two groups. Additionally, ET may improve complete response rate at 3 months post procedure.Tabled 1nMedian RD (mGycm)Median NCTET906565Non-ET1566836P = 0.05P <0.01ET + stain356425ET (no stain)55656.56Non-ET + stain926577Non-ET (no stain)646976ET + stain/non-ET + stainP = 0.02P <0.01ET + stain/non-ET (no stain)P = 0.09P = 0.01ET + dome277396ET + non-dome60591.355Non-ET + dome588388Non-ET + non-dome98605.56ET + dome/non-ET + domeP = 0.1P <0.01 Open table in a new tab