ESTRO 2023 - Abstract Book

S1952

Digital Posters

ESTRO 2023

PO-2168 3D - print technology of individually adapted vaginal and rectal applicators for brachytherapy

M. Walke 1 , J. Walke 1 , B. Röllich 1 , D. Medenwald 2 , D. Vordermark 2

1 Clinic for Radiotherapy, University Hospital Magdeburg, Magdeburg, Germany; 2 Clinic for Radiotherapy, University Hospital Magdeburg/Halle, Magdeburg/Halle, Germany Purpose or Objective Brachy-therapeutic applications of vaginal and rectal applicators have been standard in brachytherapy for years. The dose distribution, which is not always radially symmetrical, cannot be produced with standard vaginal cylinders. Rectal applicators can currently only produce non-symmetrical distributions to a limited extent, due to their firmly developed geometry. The generally limited adaptability of vaginal or rectal applicators therefore clearly restricts the applicability of these applicators in questions of deliberately induced and often necessary asymmetric dose distribution. The aim was to develop 3D printable applicators of specially defined dimensions for vaginal or rectal applications with great variability and freedom with regard to the localizable source holding points. These individualized models of these applicators can be easily converted into stable, manageable and safely applicable applicators by means of modern 3D - printing methods Materials and Methods We modelled the new applicators using CAD programs. RESIN applicators were printed according to material test series. In addition to a central access hole for the standard steel applicator (Elekta company), further 6F cylinder passages distributed equally in a circle were provided in the model. In a variation, additional centrally symmetrically distributed surface notches for clampable 6F plastic catheters were optionally provided on the cylinder. In addition to stability and pressure quality tests, extensive risk management analyses were carried out. Slippage of the catheters or the steel applicator can be prevented by means of screws and retaining sockets. The use of the printable cylinders in the corresponding organ is carried out exclusively with the use of thin biocompatible rubber covers. Only individually and personally assignable printings are used. Results Extensive application cylinder variations in and length and variations of internal catheter arrangements were printed as resin prints. Safety aspects were implemented in the form of procedural instructions, such as the necessary CT planning, print quality testing, cylinder stability testing and surface quality. The calculations for the respective irradiation planning are CT-supported and based on the TG-43 algorithm, since the resin printing material does not have high radiation attenuations. Conclusion Applicable application cylinders with individually adjustable parameters (length, diameter, number and location of usable catheter passages) could be printed and produced. The individual patient-related production of applicators is possible and approved. The use of individually designed applicators with freely definable source positions in large areas enables the planning and adaptation of a locally scalable dose distribution. S. Ouellet 1 , Y. Lemaréchal 2 , F. Berumen 1 , É. Vigneault 2 , A. Martin 2 , W. Foster 2 , M. Lavallée 2 , R. Thomson 3 , P. Després 4 , L. Beaulieu 4 1 Université Laval, Département de physique, de génie physique et d'optique, Québec, Canada; 2 CHU de Québec - Université Laval, Département de radio-oncologie et Axe Oncologie du CRCHU de Québec, Québec, Canada; 3 Carleton University, Carleton Laboratory for Radiotherapy Physics, Department of Physics, Ottawa, Canada; 4 Université Laval, Département de physique, de génie physique et d’optique, Québec, Canada Purpose or Objective MC simulations are the golden standard when it comes to dosimetry. Although they are not close to being used in treatment plan optimization, they provide realistic references for patient specific dosimetry. Such references are key components to quantify the accuracy of clinically used TPS and to study the relationship of dose-tissue responses. A MC dose recalculation applied to all delivered treatments would provide the statistically significant sample needed for these studies. The goal of this work is to build a fully automated systematic MC dose recalculation pipeline applied to permanent implant prostate brachytherapy. Materials and Methods Starting from the entire DICOM RT set, the pipeline reproduces the treatment context within the MC simulation. The sources’ model, positions and strength are extracted from the RTPLAN while the geometry of the patient is built based on the clinical contours stored in the RTSTRUCT and on prostate calcifications segmentation, when present. The dose scoring can use both CT or clinically used dose grid resolutions. To benchmark the pipeline for permanent implant brachytherapy using the Nucletron SelectSeed, TG43-like MC simulations (infinite homogeneous water medium) are validated against standard TG43 calculations for a single seed and a full treatment plan with both TOPAS and egs_brachy MC codes. For full MC patient specific dose distributions, the validation is made by comparing the simulation results of both MC codes. Finally, the MC dose recalculation is applied to a real use case, caracterising the weaknesses of the TG43 calculations. To do so, a dosimetric comparison is made between the full MC and the clinical dose distributions for 1500 patients. Results When comparing the TG43-like simulations to the TG43 calculations for 10e9 photons, the % ∆ Dlocal values for egs_brachy are within ±2.5% and ±7.5% for the single seed and the full plan, while TOPAS’s values are within ±2% and ±3%. Being a voxel-per-voxel analysis, it shows an excellent agreement between the generated MC simulations and the TG43 calculations. When comparing the full MC patient specific dose distributions using TOPAS and egs_brachy, figure 1 show a good agreement PO-2169 Systematic MC dose recalculation pipeline: a use case in permanent implant prostate brachytherapy