Gastrointestinal Cancer

PV 04 - Poster Viewing Q&A - Session 4

TU_13_2488 - Evaluation of Fiducial Tracking Availability According to Fiducial Distribution in Radiosurgery

Tuesday, September 17
2:45 PM - 4:00 PM
Location: ASTRO Innovation Hub

Evaluation of Fiducial Tracking Availability According to Fiducial Distribution in Radiosurgery
S. Ahn, S. Lee, J. Cho, and J. Kim; Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University Health System, seoul, Korea, Republic of (South)

Purpose/Objective(s): This study evaluates the fiducial tracking availability according to fiducial distribution and insertion locations in liver cancer patients whose radiosurgery was performed using a frameless robotic radiosurgery synchrony respiratory tracking system.

Materials/Methods: An analysis was performed to track three fiducials in 18 liver cancer patients who received robotic radiosurgery with three to five fiducials inserted in the liver. A total radiation dose of 45–60 Gy was prescribed to the planning target volume into three to five fractions. During radiosurgery, the fixed X-ray interval time was 60 seconds. The angles of the fiducials formed a triangle and the distance between fiducials, based on location coordinates, were analyzed. The number of X-ray images for fiducial tracking according to the angle and distance of fiducials, the radiation delivery time, and the fiducial tracking error rate were also analyzed. The fiducial tracking availability, according to the anatomic locations of inserted fiducials, was evaluated by dividing the liver into eight zones.

Results: For each of the 18 liver cancer patients, the angles of the fiducials were 60±33.1º, and the distance between fiducials was 42.4±26 mm. 1) The analysis of fiducial angles shows for six patients that one angle is 45 < x < 100º, the standard deviation of the other two angles is less than 15º, and the delivery time, number of X-ray images, and fiducial tracking error rate were reduced by 3.4%, 22.9%, and 41.0%, respectively, compared to all other patients. 2) The analysis of the distance between fiducials shows for seven patients that the distance between fiducials is 18 < x < 35 mm and the standard deviation is less than 10 mm, the delivery time, number of X-ray images, and fiducial tracking error rate were reduced by 3.9%, 27.4%, and 41.7%, respectively, compared to all other patients. 3) The analysis of the standard deviations of fiducial angle and distance shows for eight patients that the fiducial distribution forms an equilateral triangle, the delivery time, number of X-ray images, and fiducial tracking error rate were reduced by 8.4%, 27.6%, and 43.2%, respectively, compared to all other patients. 4) For ten patients for whom the fiducial insertion locations included S7 and S8, the fiducial tracking error rate was higher by 31.1% compared to the other eight patients.

Conclusion: The fiducial tracking error rate decreased as the angles formed by three fiducials were close to 60º, the distance between fiducials was near the minimum distance for fiducial tracking, and the standard deviations of the three angles and distances were reduced. Fiducial tracking availability can be improved by avoiding insertion at S7 and S8, locations that tend to move a lot as patients breathe.

Author Disclosure: S. Ahn: None.

Seung Kwon Ahn, SRI(supervisor of radiation handling)

Severance Hospital of the Yonsei University Health System

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