ESTRO 36 Abstract Book

S400 ESTRO 36 2017 _______________________________________________________________________________________________

Figure 2. This will help in determining whether the effective energy of radiation beam is less than or greater than the E max .

infill. Air cavities and lower density regions like the lungs were left open and unfilled. The slices were printed on an inexpensive and commercially available 3D printer with the inferior aspect of the patient on the printing surface. The slices were individually and collectively imaged and examined for printing accuracy. The original patient CT scan and the assembled phantom CT scan were registered together to assess the overall accuracy of the phantom construction. Results The slices took an average of 24 hours and 19 minutes to print, and the total material cost of the phantom was $524. Figure 1 shows images of the phantom with the left- most slices removed to show the interior anatomy (a), and the entire phantom assembled (b). As can be seen, the phantom fits together well, and has a high level of detail. Figure 2 shows a comparison of slices in the axial, sagittal and coronal orientations from the original patient CT image (a), and slices from the phantom CT image (b) in the same location and orientation. While material heterogeneity has been lost due to using only one material in the phantom, the anatomical and structural details agree very well between the printed phantom and the source image. The only disagreement is in the lungs, where unsupported nodules were removed prior to printing the phantom. Analysis of individual slices revealed that measurable dimensions were accurate within 0.5 mm, and the average volumetric discrepancy between printed slices and their models was 1.37%. Figure 1:

Conclusion This work presents some possible TLD tandem systems consisting of three types TL materials which are better able to estimate effective energy of a radiation beam in the 30 to 100 keV range than the presently used two TL material tandem systems. This can potentially improve dosimetry in situations where information about the effective energy of radiation is crucial such as personal monitoring. Considering the high sensitivity TLD100H, the TL material increasingly being used in personal dosimetry, tandem combinations of TLD100H,TLD200 & TLD500 or TLD100H, TLD400 & TLD500 are recommended for x or gamma radiation energy discrimination in the 30 to 120 keV range. PO-0765 Preparation and Fabrication of a Full-scale Patient-specific 3D-Printed Radiotherapy Phantom D. Craft 1 , R. Howell 1 1 The University of Texas MD Anderson Cancer Center, Radiation Physics, Houston- TX, USA Purpose or Objective Phantoms are used in a wide variety of ways for radiotherapy research and quality assurance. Generally, however, these phantoms are limited in size and complexity to represent only small treatment areas or generalized patients. 3D printing technology can make the fabrication and design of patient-specific phantoms simple and inexpensive, but has also been limited by size and complexity due to the limited size of most 3D printers and the tendency of materials to warp while being printed. We aimed to overcome these limitations by developing an effective 3D printing workflow that could be used to design and fabricate large, full-scale, patient-specific phantoms with negligible material warping errors. To demonstrate the viability of our technique we produced a full-scale phantom of a post-mastectomy patient treated at our institution. Material and Methods The clinical CT data for a post-mastectomy patient at our institution was converted into a 3D model, and then trimmed to remove the patient’s head and arms to simplify printing. The model was next sliced into eleven 2.5-cm-thick sagittal slices, which fit better and have less warping relative to axial slices. Each slice was printed using polylactic acid to represent all body tissues at 100%

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