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A semi-automated 2D/3D marker-based registration algorithm modelling prostate shrinkage during radiotherapy for
Tom Budiharto1, Pieter Slagmolen, Jeroen Hermans
1Department of Radiotherapy, University Hospitals Leuven, Belgium. tom.budiharto@uz.kuleuven.ac.be
Summary
Incorporating prostate gland shrinkage into radiotherapy patient alignment using an isotropic scaling factor reduced registration errors. However, this did not significantly alter treatment table translations compared to manual methods.
Area of Science:
- Medical Physics
- Radiation Oncology
- Image-guided radiotherapy
Background:
- Current patient alignment tools rely on manual marker matching and rigid registration.
- Prostate gland shrinkage during radiotherapy can affect alignment accuracy.
- Tracking implanted gold markers can quantify prostate shrinkage effects.
Purpose of the Study:
- To quantify the effect of prostate gland shrinkage on patient alignment during radiotherapy.
- To evaluate the impact of an isotropic scaling factor in registration for modeling prostate shrinkage.
- To compare alignment accuracy with and without accounting for shrinkage.
Main Methods:
- Eight prostate cancer patients received transrectally implanted gold markers.
- Semi-automated 2D/3D marker-based registration was used, incorporating rigid transformation and isotropic scaling.
- Orthogonal electronic portal images (EPIs) were acquired after alignment to skin tattoos.
Main Results:
- Including an isotropic shrinkage model reduced registration errors.
- The mean scaling factor observed was 0.89+/-0.09, indicating shrinkage.
- Translation offsets showed minimal difference between manual matching and the semi-automated method with scaling.
Conclusions:
- Accounting for prostate shrinkage in the registration process improves accuracy during radiotherapy.
- The observed reduction in registration errors did not translate to clinically significant changes in table translations.
- Intermarker distance decrease correlated with prostate shrinkage, not random marker migration.
