Variability of Four-Dimensional Computed Tomography Patient Models

Journal Article · Fri Feb 01 04:00:00 EST 2008 · International Journal of Radiation Oncology, Biology and Physics

DOI:https://doi.org/10.1016/j.ijrobp.2007.08.067· OSTI ID:21039771

Sonke, Jan-Jakob ^[1]; Lebesque, Joos; Herk, Marcel van ^[1]

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1. Department of Radiation Oncology, Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Amsterdam (Netherlands)

Purpose: To quantify the interfractional variability in lung tumor trajectory and mean position during the course of radiation therapy. Methods and Materials: Repeat four-dimensional (4D) cone-beam computed tomography (CBCT) scans (median, nine scans/patient) routinely acquired during the course of treatment were analyzed for 56 patients with lung cancer. Tumor motion was assessed by using local rigid registration of a region of interest in the 3D planning CT to each phase in the 4D CBCT. Displacements of the mean tumor position relative to the planned position (baseline variations) were obtained by using time-weighted averaging of the motion curve. Results: The tumor trajectory shape was found to be stable interfractionally, with mean variability not exceeding 1 mm (1 SD) in each direction for the inhale and exhale phases. Interfractional baseline variations, however, were large, with 1.6- (left-right), 3.9- (cranial-caudal), and 2.8-mm (anterior-posterior) systematic variations (1 SD) and 1.2- (left-right), 2.4- (cranial-caudal) and 2.2-mm (anterior-posterior) random variations. Eliminating baseline variations by using soft-tissue guidance decreases planning target volume margins by approximately 50% compared with bony anatomy-driven protocols for conventional fractionation schemes. Conclusions: Systematic and random baseline variations constitute a substantial portion of the geometric variability present in the treatment of patients with lung cancer and require generous safety margins when relying on accurate setup/immobilization or bony anatomy-driven correction strategies. The 4D-CBCT has the ability to accurately monitor tumor trajectory shape and baseline variations and drive image-guided correction strategies that allows safe margin reduction.

• OSTI ID: 21039771
• Journal Information: International Journal of Radiation Oncology, Biology and Physics, Journal Name: International Journal of Radiation Oncology, Biology and Physics Journal Issue: 2 Vol. 70; ISSN IOBPD3; ISSN 0360-3016
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
ANATOMY
CARCINOMAS
COMPUTERIZED TOMOGRAPHY
CORRECTIONS
FRACTIONATED IRRADIATION
IMAGES
LUNGS
PATIENTS
RADIOTHERAPY
SAFETY MARGINS