Visualization of the 3D Dosimetry for a Leipzig Brachytherapy Applicator Using 3D Slicer

appropriate distance for the sources to be placed from the skin surface. The trajectories which the sources would take were then drawn, with uniform separation, on this surface. The mould was completed by extending the surface further and then subtracting the trajectories. The complete STL file was then sent to the printer for fabrication by the Stratasys Objet500 Connex1 printer, and printed using a Rubber-like material (TangoPlus). Results: Catheters produced by Elekta for connection to the Flexitron HDR treatment unit, were successfully inserted into the 3D printed mould without damage and minimal air gaps. The patient attended clinic and had the mould positioned. The mould fitted extremely well and was comfortable for the patient. The fit far exceeded the conformity of the conventional plastic shell mould which was also made for the patient, in particular between the patient’s fingers. A CT scan of the patient’s hand with the 3D mould attached was acquired. The CT image set was imported into the Oncentra Brachy TPS (treatment planning system) manufactured by Elekta and the catheters were reconstructed. A target volume was delineated by the Consultant Clinical Oncologist and a treatment plan created to deliver the prescribed dose to the target volume. However, due to the proximity of the surrounding healthy fingers, it was determined that they would receive an unacceptably high dose. As the patient was unable to separate his fingers more it meant, unfortunately it wasn’t possible to treat him using HDR brachytherapy. A dummy run of the planned treatment was performed proving in principle the procedure was viable. Conclusions: A 3D printed mould could be created that fitted the patient’s anatomy extremely well. Channels could be created within the 3D printed mould that allowed insertion of catheters manufactured by Elekta for the radioactive source to travel along safely and accurately. We have since used the patient CT image set to create alternative positions for the catheters within a mould in order to improve the overall treatment plan by reducing the dose to the other fingers and keeping the target dose aim. For future patients an additional CT scan of the patient will be performed prior to the mould manufacturer to calculate the optimal position of the catheters within the TPS. The desired mould will then be created in the 3-Matic design software and printed. A second CT scan will be performed to verify the fit of the mould. As an initial study this was very successful as the 3D printed mould was suitable for clinical use and a better fit and easier to plan than previous manually created patient moulds.