Program Information
Evaluation of the Setup Uncertainties of Decubitus Position Using Surface Imaging
X Tang1*, Y Song1, C Obcemea1, J Lee1, Z Saleh1, C Shi2, M Chan2, J Jeong1, B Mueller1, (1) Memorial Sloan Kettering Cancer Center Westchester, West Harrison, NY. (2) Memorial Sloan Kettering Cancer Center, Basking Ridge, NJ.
Presentations
SU-I-GPD-J-102 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Decubitus position is often needed for breast electron boost. However, it is a challenging setup and might be associated with large day-to-day variations. We herein apply AlignRT surface imaging to evaluate the decubitus setup positions and assess its uncertainties.
Methods: 3 volunteers were included in the study. CDR vacuum lock mold was made for each volunteer at CT SIM. To be consistent, all volunteers were in left decubitus position with left arm raised and rested over the head. Volunteer and the mold were marked for repositioning. An AlignRT reference surface was acquired. Volunteer was then setup in the treatment room, aligned to the markers. Each volunteer was setup 6 times and for each setup the treatment surface was acquired. The the mean and standard deviation of the translational and rotational displacements were calculated for each volunteer. We also calculated the overall mean and standard deviation for all volunteers.
Results: The mean (±stdv) displacement (LONG, LAT, LONG, MAG (cm), Rtn°, Roll°, and Pitch°) for the three volunteers were are follow: Volunteer 1 (-0.89±0.33; 0.22±0.25; -0.83±1.12; 1.59±0.49; -3.88±1.46; 5.22±3.11; 2.13±0.61); Volunteer 2 (-0.02±0.17; 0.58±0.75; -0.21±0.59; 0.80±0.80; -0.20±1.71; 0.17±2.17; -0.55±1.50); Volunteer 3 (-0.22±0.18; 0.45±0.61; 0.90±1.33; 1.47±0.92; 1.28±2.35; 2.15±3.07; 0.27±0.67). The overall mean displacements were (-0.38±0.22; 0.42±0.54; -0.05±1.01; 1.29±0.74; -0.93±1.84; 2.51±2.78; 0.62±0.93).
Conclusion: The translational setup uncertainly seems clinically reasonable—with averages less than 0.5 cm. The rotation and pitch overall averages were smaller than 1° which was within acceptable setup uncertainties as well. However, the roll overall average was 2.51° which might affect treatment accuracy. Further simulation is needed to assess if there is meaningful dosimetric uncertainty associated with our observation.
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