Benefit of 3D image-guided stereotactic localization in the hypofractionated treatment of lung cancer

Lu Wang, Ph.D., Steve Feigenberg, M.D., Kamen Pasklev, M.S., Lili Chen, Ph.D., C-M Ma, Ph.D.

Fox Chase Cancer Center, Philadelphia, PA 19111

Purposes: To investigated the benefit of image-guided stereotactic localization in the hypofractionated treatment for medically inoperable non-small cell lung cancer.

Materials & Methods: A stereotactic body localizer (SBL) system was used for patient immobilization, image registration among multi-phase CT simulation, and image-guided stereotactic localization. The simulation scans consist of 3 sets of CT images taken at free breathing, breath-holding at maximum inhalation and exhalation, respectively. Target delineation was performed on all 3 sets of images and the combination of the targets forms a composite gross-target volume (GTV), which accounts for target motion due to respiration. Treatment planning was performed on the planning-target volume (PTV) using 3 mm margin. Prior to each treatment, a localization CT scan using a CT-on-rails was obtained to check the setup uncertainty. Couch shifts were made based on the changes of the stereotactic coordinates of three pre-selected bony landmarks. In this retrospective treatment dose verification, we performed image fusion between the simulation CT scan and each pre-treatment CT scan to obtain the same target and critical structure information. The same treatment plans were re-loaded onto each pre-treatment CT scan with their respective stereotactic coordinate system. The changes in dose distributions were assessed by dose-volume histograms of the PTV and the critical structures before and after isocenter corrections which were prompted by image guided stereotactic localization. We compared D₉₅, D₉₉, and V₉₅ for the PTV and GTV, and V₂₀ and V₃₀ for the ipsilateral lung.

Results: Our retrospective study for 10 patients with 40 dose reconstructions showed that the average D₉₅, D₉₉, and V₉₅ of the PTVs are 92.1%, 88.1%, and 95.8% of the planned values before isocenter corrections. With the corrections, these values are all improved to 100% of the planned values.

Conclusions: 3D image guidance is crucial for stereotactic radiotherapy of lung tumors.