Interfraction prostate rotation determined from in-room computerized tomography images.

Area of Science:

• Radiation Oncology
• Medical Imaging
• Prostate Cancer Treatment

Background:

• Fiducial markers (FMs) are standard for correcting prostate interfraction translation.
• Accurate assessment of prostate rotation is crucial for effective radiotherapy.

Purpose of the Study:

• To quantify prostate rotation using fiducial marker coordinates versus anatomical contours.
• To evaluate an adaptive technique for reducing systematic rotation errors.

Main Methods:

• Daily CT scans (n=346) from 10 prostate cancer patients with FMs were analyzed.
• Prostate rotation was determined using FM coordinates and CT contours of the prostate and rectum.
• An adaptive method using 6 CT scans was tested to reduce sagittal plane rotation errors.

Main Results:

• Fiducial markers showed systematic rotation errors of 7.6° (sagittal), 7.7° (transverse), and 5.0° (coronal).
• Contour-based analysis revealed 10.1° systematic and 7.7° random sagittal plane errors, correlating poorly with FM data (r=-0.017).
• Adaptive technique reduced systematic sagittal rotation error by 43% to 5.6°.

Conclusions:

• Prostate rotation is a significant source of error in radiotherapy.
• Anatomical contours provide a more accurate measure of prostate rotation than fiducial markers.
• CT image guidance utilizing anatomical borders is essential for precise prostate cancer treatment.