Bradley Pieters
Academic Medical Center in Amsterdam, The Netherlands
Head of the Brachytherapy department

MRI is imaging modality of preference for treatment planning in cervical brachytherapy. GEC-ESTRO recommendations were originally developed in the era that 0.5-1.5T MRI machines were widespread in use. Nowadays more 3.0T machines are installed and the question is what is the magnitude of image distorsions and its impact on the accuracy of 3D dose distribution calculation. Phantom studies with a synthetic applicator shows minimal shifts at the tip of the intrauterine tube of less than 0.1 mm. When investigated in patients the difference found in DVH parameters caused by image distorsion is about 5%.

Another uncertainty is the accuracy of addition of external beam to brachytherapy dose distribution. Particularly with modern techniques as IMRT/VMAT it is questionable how homogeneous the dose distribution in rectum and bladder is. A way to calculate summated dose distribution is by performing deformable image registration (DIR). When comparing between DIR or assuming homogeneous dose on OAR differences of less than 2 Gy EQD2 were found. EBRT dose distributions can be considered uniform in bladder and rectum.

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