A Comprehensive Assessment by Tumor Site of Patient Setup Using Daily MVCT Imaging From More Than 3,800 Helical Tomotherapy Treatments
Received 3 July 2008; received in revised form 6 November 2008; accepted 13 November 2008.
Purpose
To assess patient setup corrections based on daily megavoltage CT (MVCT) imaging for four anatomic treatment sites treated on tomotherapy.
Method and Materials
Translational and rotational setup corrections, based on registration of daily MVCT to planning CT images, were analyzed for 1,179 brain and head and neck (H&N), 1,414 lung, and 1,274 prostate treatment fractions. Frequencies of three-dimensional vector lengths, overall distributions of setup corrections, and patient-specific distributions of random and systematic setup errors were analyzed.
Results
Brain and H&N had lower magnitude positioning corrections and smaller variations in translational setup errors but were comparable in roll rotations. Three-dimensional vector translational shifts of larger magnitudes occurred more frequently for lung and prostate than for brain and H&N treatments, yet this was not observed for roll rotations. The global systematic error for prostate was 4.7 mm in the vertical direction, most likely due to couch sag caused by large couch extension distances. Variations in systematic errors and magnitudes of random translational errors ranged from 1.6 to 2.6 mm for brain and H&N and 3.2 to 7.2 mm for lung and prostate, whereas roll rotational errors ranged from 0.8° to 1.2° for brain and H&N and 0.5° to 1.0° for lung and prostate.
Conclusions
Differences in setup were observed between brain, H&N, lung, and prostate treatments. Patient setup can be improved if daily imaging is performed. This analysis can assess the utilization of daily image guidance and allows for further investigation into improved anatomic site-specific and patient-specific treatments.
∗Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, WI
†Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Madison, WI
Reprint requests to: Leah K. Schubert, M.S., University of Wisconsin School of Medicine and Public Health, Department of Medical Physics, Wisconsin Institutes for Medical Research, 1111 Highland Avenue, Room 1005, Madison, WI 53705. Tel: (608) 262-2170; Fax: (608) 262-2413
This work was funded by National Institutes of Health National Cancer Institute Grant PO1 CA088960.
Conflict of interest: The authors T. R. Mackie and E. T. Soisson have financial interests in TomoTherapy, Inc., and therefore may have a potential conflict of interest. No other authors report potential conflicts of interest.
ABSTRACT