ESTRO 36 Abstract Book

S971 ESTRO 36 2017 _______________________________________________________________________________________________

3 Hospital Clinica Benidorm/Hospital La Fe, Radiotherapy, Benidorm/Valencia, Spain

Purpose or Objective ABS and GEC-ESTRO recommend magnetic resonance imaging (MRI) in T2-sequence as preferable modality in image-guided brachytherapy for gynecological malignancies. On the other hand, widespread availability of the applicator libraries in the brachytherapy treatment planning systems (TPS) allows global approach to the issue of the applicator modeling. The aim of this work is to present a method to incorporate complete applicator geometries in SagiPlan, (not only single channels), based on the technical data available from manufacturer and then develop a marking system which allows recognizing a defined applicator (Vienna-type applicator of Eckert & Ziegler BEBIG) in the MR image series with utmost possible precision for the library reconstruction. Material and Methods The investigated applicator model is Vienna-type applicator, consisting of tandem with a ring for possible interstitial component from Eckert&Ziegler BEBIG (Berlin, Germany) together with a model available in the library of the SagiPlan® TPS from Eckert&Ziegler BEBIG. 3D model of the applicator was reconstructed independently, using open-source modeling software FreeCAD (www.freecad.org). The presented reconstruction technique is based on the placement of three vitamin A capsules, clearly visualized in T2 MRI, embedded in the material layer giving enough contrast for the capsule recognition. The position of the marking capsules with respect to the applicator geometry is known precisely, due to placement of the attachments in 3D model reconstructed in FreeCAD and verified against technical specifications of the applicator. The accessory attachments to the applicator are produced on the 3D printer from polylactide polymer material (PLA) and carry the marking capsules inside.

On figures: a) Assembly for rapid strand radioactivity measurement. 1- short transport container; 2- tweezers to hold strand; 3- cylindrical tube (barrel); 4- sterile coating; 5- plastic container; 6- rapid strand seeds; 7- well-chamber. b) Measured values of Rapid strand seeds radioactivity. c) Strand cutting procedure devices. 8- Transport container with cut-outs for 'safely and clean outside cutting” of required strand; 9- spacing jig; 10- seat for container to prevent its rotation on the table; 11- cut-out for finger in container to prevent rotating of spacing jig inside the container. d) Removing of cut-up strands from container. 12- container; 13- metal shielding cover; 14- lead glass; 15- seat for container. Results Summarizing the measurement of every single seed activity might be found the intra-op calibration factors for rapid strand (containing 4/5/6 seeds) inserted into well- chamber. They are: total activity 2,20 mCi strand of 4 seeds produce 121,4 pC/10s corrected for pressure and temperature reading of electrometer, overall activity 3,28 mCi strand of 6 seeds gives 181,6 pC/10s corrected for pressure and temperature reading of electrometer. Conclusion Described quality control procedure provide confidence that total seeds radioactivity of implanted into patient in LDR brachytherapy procedure correspond to intended value. Sterile conditions for rapid strands are guaranteed and therefore procedure can be accepted for intra-op using. The exposure dose received by personal during this procedure is negligibly small. EP-1795 A novel MRI markers system in applicator reconstruction for brachytherapy A. Otal 1 , J. Richart 1 , C. Domingo 1 , S. Rodriguez 1 , P. Rodriguez-Meijide 2 , I. Fotina 2 , M. Santos 1 , J. Perez- Calatayud 3 1 Hospital Clinica Benidorm, Radiotherapy, Benidorm, Spain 2 Eckert & Ziegler BEBIG GmbH, Marketing, Berlin, Germany

Results In order to validate the accuracy of the reconstruction with use of the model described above, we acquired T2 MRI sequence of the Vienna applicator in water with accessory attachments in place. The images were entered