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A Cognitive Fusion-guided Prostate Biopsy Using Multiparametric Magnetic Resonance Imaging and Transrectal Ultrasound
Published on: March 21, 2025
Prostate rotation detected from implanted markers can affect dose coverage and cannot be simply dismissed
Qingyang Shang1, Lawrence J Sheplan Olsen, Kevin Stephans
1Department of Radiation Oncology, Cleveland Clinic, Cleveland, OH 44195, USA.
Journal of Applied Clinical Medical Physics
|May 9, 2013
Summary
Prostate rotations in radiation therapy can significantly impact treatment accuracy, leading to geometric and dosimetric errors. Compensating for these rotations with translational shifts improves accuracy and reduces dose coverage discrepancies.
Area of Science:
- Radiation Oncology
- Medical Physics
- Image-Guided Radiation Therapy (IGRT)
Background:
- Daily prostate displacements, including rotations, are detectable using implanted markers during radiation therapy.
- Observed rotation magnitudes often exceed the capabilities of standard treatment couches, posing a challenge for accurate patient positioning.
Purpose of the Study:
- To quantify the geometric and dosimetric effects of uncorrected prostate rotations (ROT_NC) versus rotations compensated by translational shifts (ROT_C).
- To evaluate the impact of these registration methods on prostate dose coverage under varying planning margins.
Main Methods:
- Retrospective analysis of 43 kilovoltage cone-beam CTs (KV-CBCT) from five patients with implanted markers.
- Manual contouring of prostate, bladder, and rectum; benchmark registration via manual alignment of planning CT and CBCT contours.
- Comparison of two marker registration methods: ROT_NC (six degrees of freedom, uncorrected rotations) and ROT_C (three degrees of freedom, rotations compensated into translational shifts).
- Evaluation using center of mass distance (CMD) and overlap index (OI); dosimetric analysis by comparing prostate clinical target volume (CTV) dose coverage.
Main Results:
- Prostate rotations were predominantly along the left-right axis, with systematic (4.6°) and random (4.1°) components.
- Significant differences in CMD (>5 mm) observed between ROT_NC and ROT_C when rotation angles exceeded 10° (85.7% of fractions).
- With larger margins (6 mm/4 mm posterior), ROT_C showed significantly less average difference in D99 (-3.6 ± 9.0%) compared to ROT_NC (-8.0 ± 12.3%) (p = 0.01).
- With smaller margins (4 mm/2 mm posterior), ROT_C still demonstrated improved D99 accuracy (-15.1 ± 15.2%) over ROT_NC (-22.0 ± 16.2%) (p < 0.05).
Conclusions:
- Prostate rotations are a significant factor in radiation therapy and should not be disregarded.
- The impact of rotational errors is dependent on the distance between the isocenter and the centroid of implanted markers, as well as the magnitude of rotation.
- Compensating for prostate rotations with translational shifts (ROT_C) can mitigate geometric and dosimetric inaccuracies, particularly under tighter planning margins.
