Evaluation of set up error in Exactrac Dynamic (EXTD) system for treating thoracic, abdominal and pelvic cancer patients

Abstract

Background: ExacTrac Dynamic (EXTD) is a non-ionizing technology used for patient position verification and has been implemented as an alternative to radiation-based positioning systems. However, a limitation of EXTD is that it cannot directly assess internal organ motion. Objective: This study aims to evaluate the setup deviation in patient positioning using the ExacTrac Dynamic (EXTD) system for patients undergoing radiotherapy for thoracic, abdominal, and pelvic cancers. Methods: A total of 60 patients diagnosed with cancer in the thoracic, abdominal, or pelvic regions were positioned using the Surface-Guided Radiation Therapy (SGRT) function of the EXTD system. All patients received treatment with Volumetric Modulated Arc Therapy (VMAT) using the Varian TrueBeam linear accelerator at the Cancer Hospital’s Radiation Oncology Department. Cone-Beam Computed Tomography (CBCT) was used to verify setup deviations in six directions: vertical, longitudinal, lateral, pitch, roll, and yaw. CBCT images were compared against reference images from the treatment planning system. The mean difference between the EXTD setup and CBCT verification were analyzed to determine whether they remained within the limits set by the International Atomic Energy Agency (IAEA). Results: The mean difference recorded by SGRT using EXTD in the six directions were as follows: Vertical: -0.20 ± 1.87 mm (thoracic), -1.99 ± 1.99 mm (abdominal), -1.36 ± 2.47 mm (pelvic), Longitudinal: -1.76 ± 1.84 mm (thoracic), -1.50 ± 3.00 mm (abdominal), -0.93 ± 4.49 mm (pelvic), Lateral: -0.58 ± 1.40 mm (thoracic), -2.29 ± 2.58 mm (abdominal), -1.12 ± 2.14 mm (pelvic), Yaw: -0.63 ± 0.96° (thoracic), -0.47 ± 1.23° (abdominal), -0.28 ± 0.81° (pelvic), Pitch: -0.32 ± 0.70° (thoracic), 0.09 ± 1.27° (abdominal), -0.08 ± 0.93° (pelvic), Roll: 0.07 ± 0.80° (thoracic), 0.09 ± 0.58° (abdominal), 0.23 ± 0.93° (pelvic)All reported values were within the standard tolerances specified by the IAEA. Conclusion: The study found that patient setup errors using the ExacTrac Dynamic (EXTD) system were within acceptable limits based on international standards. EXTD can replace CBCT in some cases, especially for patients with tumors in the upper chest, upper abdomen, or pelvis, where internal organ motion is minimal. Using EXTD instead of CBCT in patients with low organ movement can reduce the number of repeated scans and the total imaging dose, while keeping treatment accuracy within IAEA standards.