Assessment of Respiratory Tumor Movement using 4D Computed Tomography for Stereotactic Radiosurgery in Lung Tumor

ABSTRACT

PURPOSE: To assess the respiratory tumor movement using 4D-CT (4-dimensional computed tomography) for minimizing setup and target volume uncertainty of body-frame based stereotactic radiosurgery (SRS) in lung tumor. MATERIALS AND METHODS: Fifty-seven stereotactic radiation therapies with respiratory gating system in 44 patients (two targets in seven patients and three in three patients) were executed in Asan Medical Center from May 2005 to June 2006. We used respiratory gating system consisted of RPM (Real-time Positioning Management system, Varian, USA) and 4D-CT (GE healthcare, USA), if tumor movement was exceeding 5 mm by respiration on fluoroscopy. Accurate tumor movement on reconstructed 4D-CT image was determined for respiratory gated therapy. Respiratory gated therapy was done if tumor movement was exceeding 5 mm, and non-gated therapy was done if it was below 5 mm. RESULTS: Forty-five tumors were treated with supine position, and the other twelve were with prone position. Median tumor movement (3-dimensional) by respiration was 8.78+/-5.30 mm, and it was mostly affected by superior-inferior movement (8.53+/-5.23 mm). Tumor movements were different by tumor location, whether upper (5.38+/-2.85 mm) or lower (10.12+/-5.08 mm) lobe (p=0.015). Tumor movement was exceeding 5 mm in 27 (47.3%) tumors, and below 5 mm in 30 tumors in 4D-CT evaluation. Tumor movements on adopted respiratory gated phase were wholly below 5 mm, and its median value was 3.70+/-1.13 mm. CONCLUSION: Assessment of respiratory tumor movement using 4D-CT and gating system was helpful for minimizing target volume uncertainty. As a result, image-guided radiation therapy could improve the treatment accuracy of high precision stereotactic radiosurgery