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Initial experience with megavoltage (MV) CT guidance for daily prostate alignments
Katja M Langen1, Yashan Zhang, Rhonda D Andrews
1Department of Radiation Oncology, M. D. Anderson Cancer Center Orlando, Orlando, FL 32806, USA. Katja.langen@orhs.org
Summary
Fiducial markers improve megavoltage CT (MVCT) image registration accuracy for prostate cancer patients undergoing TomoTherapy. This method reduces alignment errors and inter-user variability compared to anatomy or contour-based techniques.
Area of Science:
- Radiotherapy
- Medical Imaging
- Radiation Oncology
Background:
- TomoTherapy Hi*ART units offer on-board megavoltage computed tomography (MVCT) for daily image acquisition.
- Accurate patient alignment using MVCT images registered with planning CT images is crucial for calculating couch shifts in prostate cancer treatment.
- Manual registration techniques, including fiducial markers, CT anatomy, and kVCT contours, are used for MVCT-to-CT image alignment.
Purpose of the Study:
- To evaluate three manual techniques for registering daily MVCT images with planning kilovoltage (kV) CT images for prostate cancer patient alignment.
- To compare the accuracy and inter-user variability of fiducial marker-based, anatomy-based, and contour-based registration methods.
Main Methods:
- One hundred and twelve alignments from 3 prostate cancer patients were analyzed.
- Radiation therapists and a physician performed retrospective registrations using anatomy and contour-based techniques.
- Reference alignments were established using the center-of-mass of three fiducial prostate markers.
Main Results:
- Marker-based registration showed the highest agreement with reference alignments and the least inter-user variability.
- Anatomy-based registration performed better than contour-based registration when fiducial markers were not used.
- Radiation therapists' alignments differed by > or = 3 mm from reference alignments in 24%, 33%, and 3% (AP, SI, Lat) for marker-based, versus 55%, 48%, and 21% for contour-based techniques.
Conclusions:
- Fiducial markers significantly enhance MVCT image guidance by reducing inter-user variability in image registration for prostate cancer radiotherapy.
- When fiducial markers are unavailable, anatomy-based registration is a more reliable alternative to contour-based registration for patient alignment.