ESTRO 36 Abstract Book

S404 ESTRO 36 _______________________________________________________________________________________________

Material and Methods Five different TL materials TLD100, TLD100H, TLD200, TLD400 and TLD500, were investigated. Each type of TL dosimeter was irradiated to the eight different qualities of x-radiation. Mean of the response of the 5 dosimeters for a certain x-radiation with effective energy Eeff was taken as the energy dependent TL response of that type of TL dosimeter. For each type of TL detector, energy dependence curves were determined by fitting the experimental results with a polynomial function. Tandem curve pairs for six different combinations were generated; ;1.TLD100H, TLD200, TLD400, 2.TLD100H, TLD200, TLD500, 3.TLD100H, TLD400, TLD500, 4.TLD100H, TLD200, TLD400,5.TLD100, TLD200, TLD500 and 6.TLD100, TLD400, TLD500.TL response ratios at different energies was calculated and compared with two TL material tandem systems. Results All Tandem curves exhibited maximum TL response ratio, E max , at approximately 45 keV, with reduction in TL response ratios at energies above and below this energy level. All tandem combinations, except the combinations (1) and (4) showed that at energies in the 30 to 80 keV range, where the TL response ratio of tandem pair (i) is same, TL response ratio tandem pair (ii) differs by 20-30%, Figure 2. This will help in determining whether the effective energy of radiation beam is less than or greater than the E max .

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% 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