3137 - Utility of Intrafraction Deep Inspiration Breath Hold CBCT in Detecting Tumor Motion during Lung and Abdominal SBRT
Presenter(s)
S. Srinivasan1, M. R. Dieringer2, R. Fuller2, J. C. Jean2, A. G. McKim2, M. R. Knight1, D. Pokhrel1, R. C. Zellars3, and O. Ishaq Jr1; 1Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, IN, 2Indiana University, Indianapolis, IN, 3Indiana University Department of Radiation Oncology, Indianapolis, IN
Purpose/Objective(s): To assess the utility of intrafraction deep inspiration breath hold (DIBH) CBCT to detect and correct for tumor motion in addition to initial DIBH CBCT in SBRT of lung and abdomen tumors.
Materials/Methods: In this IRB approved retrospective study, we reviewed 33 patients (23 lung and 10 abdominal) SBRT treatment with DIBH motion management technique. All patients DIBH parameters (threshold, duration, number of breath holds to complete treatment) were reviewed from CT simulation to treatment delivery. The SBRT treatments were planned on DIBH CT with 6MV FFF/10MV FFF VMAT technique in eclipse 15.6 planning system. Treatments were delivered on TrueBeam/Edge machines with 6 DoF couch and RPM for motion management. All patients received at least 1 intrafraction DIBH CBCT to assess tumor motion during treatment in addition to initial setup DIBH CBCT. None of these patients had fiducial markers for tumor tracking. Active DIBH monitoring was done using RPM, with 3mm threshold. Initial and intrafraction DIBH CBCT images were reviewed on offline review module in Aria to detect shift in couch positioning between initial and intrafraction DIBH CBCT to account for tumor motion.
Results: Out of 33 patients, 162 SBRT fractions were reviewed. 119 of these fractions (73.5%) included an intrafraction DIBH CBCT. Among the 119 fractions, 11.8% demonstrated translational shifts greater than 5 mm, and 18.5% demonstrated rotational shifts greater than 1 degree. In the lung SBRT cohorts 5 of 23 patients had at least one shift more than 5mm, 6 of 85 fractions had at least one shift more than 5 mm. In the abdominal SBRT cohorts 5 of 10 patients had at least one shift more than 5mm, 19% of the abdominal SBRT fractions had at least one shift more than 5mm. Number of breath holds per treatment fraction in lung and abdominal SBRT cohorts were 6.0±3.1 (range 2-16) and 5.9±3.6 (range 2-15) respectively.
Conclusion: Deep inspiration breath hold is widely used as a motion management technique to reduce GTV to PTV margin. In this study we observed that intrafraction DIBH CBCT can be an effective tool to detect and correct tumor motion during SBRT treatments. Patient selection plays an important role in reducing tumor motion during SBRT treatment with DIBH. In this study we observed that the patients that required more than 5 breath holds to complete a SBRT fraction had higher probability for intrafraction tumor motion due to prolonged treatment delivery time.