Program Information
Quantifying Tumor Positional Reproducibility Using CBCT for Patients Undergoing Breath-Hold SBRT with SDX
D Wieczorek*, V Mishra , A Gutierrez , Miami Cancer Institute, Miami, FL
Presentations
MO-RPM-GePD-J(B)-6 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Joint Imaging-Therapy ePoster Lounge - B
Purpose: The purpose of this study is to quantify the positional reproducibility of tumors undergoing breath-hold technique with the SDX spirometry system during SBRT treatments as measured with CBCT.
Methods: Two SBRT patients were simulated with the use of the SDX for breath-hold motion management. SBRT plans (5 fractions) were generated in Eclipse. SDX breath-hold CBCT were obtained prior to each treatment for inter-fractional position verification. For this study, each breath-hold CBCT was retrospectively registered to the breath-hold planning CT using bony anatomy landmarks. The planning CT GTV was then copied into each of the five CBCTs, GTV_CT. The GTV was also identified and drawn into each CBCT, GTV_CBCT. The difference in the center of mass between the GTV_CT and GTV_CBCT were then calculated. Of the two patients in the study, one had a right pleural mass and one had a right lower lobe lesion. Each patient had 5 CBCTs available for analysis.
Results: The results show that the right pleura lesion was found to have good breath-hold reproducibility, less than 1 mm variability in centroid displacement amongst the five fractions. On the other hand, the right lower lobe lesion was less reproducible with a mean centroid displacement of 1.0 cm (0.31 cm SD). GTV volume changes between the CT and CBCT range from 5% to 15% increase for the right pleural mass and right lower lobe lesion, respectively. Increased volume in CBCT can be explained since acquisition occurs over 60 seconds.
Conclusion: Inconsistent tumor positional reproducibility was noted when using the SDX breath-hold management technique for highly mobile island lesions. However, consistent reproducibility was noted for tethered lesions. It is critical to use IGRT techniques using tumor-based CBCT to Planning CT match in addition to breath-hold techniques prior to treatment.
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