SU‐E‐T‐586: Utrecht Applicator Reconstruction in MRI‐Based Cervix Gynaecological Brachytherapy

Purpose: GYN GEC‐ESTRO recommendations stated the convenience of performing a 3D magnetic resonance imaging (MRI)—based treatment planning for brachytherapy in cervical cancer. Several applicators have been developed for combining intracavitary/interstitial brachytherapy like the Utrecht applicators consisting of a tandem plus colpostats with plastic needles inserted for which no dummies have been developed. The objective of this work is to describe our experience in the MRI‐based reconstruction of the Utrecht applicators. Methods: At our department Utrecht applicators are used in cervical cancer HDR brachytherapy (4 fractions of 7 Gy), after 45–50 Gy of 3DCRT. For each application, MR scans with applicator in situ are made. Two different MRI modalities have been used to acquire the images that are imported in Oncentra MasterPlan (OMP) treatment planning system. a) Firstly, the sequence of images was acquired in a GEMS SIGMA EXCITE MRI Unit (strength 1.5T). See Perez‐Calatayud et al. (R&O 2009) for the details of the process for intracavitary catheters. b) Lately the acquisition is done in a Siemens TrioTim MRI unit (strength 3T), using a 3D sequence based on acquired coronal images (dedicated to the geometric reconstruction), in conjunction with transverse images (intended to the definition of the VOI). Regarding the reconstruction of the needles, the retraction is set on OMP with the measuring distance tools on the paracoronal/parasagital reconstructed planes that contain the needle. The black hole corresponding to the needle position in the transverse view is also used.Results: Several examples are presented to illustrate the described process, which allows the reconstruction of the Utrecht applicators without any dummy phantom. With the 3T technique the image quality has been improved and the reconstruction has been enhanced. Conclusions: A fast and efficient method for the Utrecht applicator reconstruction based on 3T MRI data acquisition has been established.