The purpose of this study was compare embolization of the gastroduodenal artery (GDA) using standard pushable coils with the Interlock detachable coil (IDC), a novel fibered mechanically detachable long microcoil, in patients scheduled for selective internal radiotherapy (SIRT). Fifty patients (31 male and 19 female; median age 66.6 ± 8.1 years) were prospectively randomized for embolization using either standard coils or IDCs. Procedure time, radiation dose, number of embolization devices, complications, and durability of vessel occlusion at follow-up angiography were recorded. The procedures differed significantly in time (14:32 ± 5:56 min for standard coils vs. 2:13 ± 1:04 min for IDCs; p < 0.001); radiation dose for coil deployment (2479 ± 1237 cGycm² for standard coils vs. 275 ± 268 cGycm² for IDCs; p < 0.001); and vessel occlusion (17:18 ± 6:39 min for standard coils vs. 11:19 ± 7:54 min for IDCs; p = 0.002). A mean of 6.2 ± 1.8 coils (n = 27) were used in the standard coil group, and 1.3 ± 0.9 coils (p < 0.0001) were used in the IDC group (n = 23) because additional pushable coils were required to achieve GDA occlusion in 4 patients. In 2 patients, the IDC could not be deployed through a Soft-VU catheter. One standard coil dislodged in the hepatic artery and was retrieved. Vessel reperfusion was noted in only 1 patient in the standard coil group. Controlled embolization of the GDA with fibered IDCs was achieved more rapidly than with pushable coils. However, vessel occlusion may not be obtained using a single device only, and the use of sharply angled guiding catheters hampered coil pushability.