Abstract Book

S930

ESTRO 37

Conclusion QA results for SRT plans based on gamma index evaluation did not depend on the spatial resolution of the measurement arrays. This may indicate that the standard 2D array phantoms such as Delta4+ designed for patient- specific QA of IMRT plans can be successfully used also for patient-specific QA of SRT plans. EP-1737 The ADAM-pelvis phantom: from DICOM data to a patient-like model W. Johnen 1,2 , N. Niebuhr 1,2,3 , A. Runz 1,2 , G. Echner 1,2 1 German Cancer Research Center dkfz, Medical Physics in Radiation Oncology, Heidelberg, Germany 2 National Center for Radiation Research in Oncology, Heidelberg Institute for Radiooncology, Heidelberg, Germany 3 Heidelberg University, Department of Physics and Astronomy, Heidelberg, Germany Purpose or Objective Anthropomorphic phantoms enable controlled simulation of organ motion for investigations in MR-guided radiotherapy. These phantoms should enable a systematic end-to-end testing including MRI and CT as well as dose measurements. This was realized with the realization of the ADAM-pelvis phantom (Anthropomorphic, Deformable And Multimodal). Material and Methods MRI and CT DICOM data of patients is used as template to build organ- and bone-models by using segmentations and transforming these to virtual models using the software Geomagic® Freeform® and Autodesk Inventor. Modifications e.g. compartments, production of casts for casting moulds, cavities, joining elements, application for localizers and pockets for dosimetric films or optically stimulated luminescence detectors (OSLD) are inserted for production of the models. Different 3D-printing methods are used for production of the casts and bone-models, whereas the organ-models are built with variable cast techniques using different types of silicone. The type of silicone which is used was optimized by means of its magnitude of elasticity, stability and imaging properties in MRI and CT. Peanut oil, differently loaded agarose gels, and Vaseline® were used as surrogates for the different types of tissues e.g. adipose, muscle and bone marrow. Results : The cast was realized using a cylindrical PMMA case to build a complete pelvic phantom that includes pelvic bones, bladder, prostate and rectum. To imitate interfractional volume variations of the bladder, it can be filled with varying volumes of water. Rectum dilatation is mimicked with a balloon which can be inserted and inflated with water or air. To localize bladder and prostate motion, markers made of silicone are included on their surface, which are visible in MRI. Small pockets are included on the surface of the bladder and rectum to position OSLDs and dosimetric films for dose measurements. In feasibility studies, the reproducibility of organ motion was proven with accuracy of 1mm. These studies were based on the verification of the end-to-end testing, feasibility of dose measurements with OSLDs and dosimetric films.

Conclusion With the ADAM-pelvis phantom, the methodological basis was realized to build phantoms that enable end-to-end testing in MR-guided radiotherapy. These can further be used to build even more complex functional models. The combination of 3D-printing methods, organs made of silicone and different mixtures of gels were proven to be suitable to build an anthropomorphic phantom. It was shown in various studies that patient-like motion induced uncertainties during radiotherapy are well mimicked by the phantom. Motion and dilatation can be identified by localizers. Using dosimeters, the applied dose to the bladder and rectum can be determined. In a next step the dose distribution in the prostate could be determined by using dosimetric gel. EP-1738 3D printed material uncertainty and its consequences for radiation oncology applications D. Craft 1 , S. Kry 1 , P. Balter 1 , M. Salehpour 1 , W. Woodward 2 , R. Howell 1 1 The University of Texas MD Anderson Cancer Center, Radiation Physics, Houston, USA 2 The University of Texas MD Anderson Cancer Center, Radiation Oncology, Houston, USA Purpose or Objective There has been growing interest recently in 3D printing technology in the field of radiation oncology. This is because 3D printing can simply and inexpensively fabricate patient-specific devices such as tissue compensators, boluses, and phantoms. However, most 3D printing materials have not been well characterized, including their radiologic tissue-equivalence. The purposes of this study were to (1) determine the variance in Hounsfield Units (HU) for printed objects, (2) determine if HU varies over time, and (3) calculate the clinical dose uncertainty caused by these material variations in a variety of common use cases. Material and Methods For a sample of 10 printed blocks each of PLA, NinjaFlex, ABS, and Cheetah, the average HU and physical density were tracked at initial printing and over the course of 5 weeks, a typical timeframe for a standard course of radiotherapy. After initial printing, half the blocks were stored in open boxes, the other half in sealed bags with desiccant. Variances in HU and density over time were evaluated for the four materials. Various clinical photon and electron beams were used to evaluate potential errors in clinical depth dose as a function of assumptions made during treatment planning. The clinical depth error was defined as the distance between the correctly calculated 90% isodose line and the 90% isodose line