AbstractID: 6760 Title: Evaluation of a Patient Setup and Monitoring System for 3D Conformal and IntensityModulated Radiotherapy
Three-dimensional conformal radiotherapy requires accurate localization of target with respect to
the geometry of the treatment beams. While modern imaging technologies allow us to visualize
and segment the target and normal structures with increasing ease and accuracy, transferring
these structures into the treatment room coordinates requires accurate setup and minimal patient
movement thereafter. We tested a commercial camera system (ExacTrac, BrainLAB Inc,
Redwood City, CA) using reflective markers placed on the patient body for patient setup and
monitoring patient movement. A phantom study was performed where 4-7 markers were used
with marker shifts ranging from 0-5 mm. The phantom was CT-scanned with both 1.5mm and
3.0mm slice thickness. For small (2mm) marker shifts, the system consistently repositioned the
target within 1mm with the 1.5-mm data. When 7 markers were used with 3 markers shifted
5mm in random directions, the system was able to reposition the target within 2mm. The
performance with the 3.0-mm data was slightly worse which became negligible when 7 markers
were used. The system was used to monitor a cranial IMRT treatment. The patient was
immobilized with an Aquaplast mask and localized using the conventional 3-point technique.
Four markers were placed on the patient’s anterior head and data were recorded every 10
seconds during the treatment. Inter-fractional setup variations as large as 2.8mm were seen and
patient movement was typically 1.5-2 mm during the 12-minute treatment time. Our study
indicates that the system can be used for patient setup and monitoring with sub-millimeter
accuracy.