ESTRO 38 Abstract book

S918 ESTRO 38

a Varian Clinac 2100CD using 10 MV dual arc VMAT with collimator angles 350°/10°. All treatment plans passed our internal pre-treatment QA protocol. Agfa HealthCare supplied the OSL-film and flying-spot CR- 15-X-engine based reader used for these experiments. The OSL-film was positioned within a 20 cm stack of water- equivalent RW3 at 10 cm depth and the measured signal was scanned and erased 5 min after each irradiation. A class-solution specific OSL-calibration consisted of a uniformity correction and a linear out-of-field dose correction. Dose measurements were compared to the calculations using 3%/3mm gamma evaluation (both global and local normalization) with a low dose exclusion threshold set to 30% of the prescribed dose. Results Plan properties and gamma agreement scores (γAS) are compiled in Table 1. The median γAS was 96.7% (range: 91.0% - 99.3%) and 93.0% (range: 87.0% - 96.6%) for global and local normalization respectively. The class solution specific calibration was able to model both the infield dose and the dose gradients (Figure 1c-d). The zones with a mixture of in-field and out-of-field spectra (arrow in Figure 1b) performed typically worse for all patients.

Purpose or Objective In this study, it is aimed to propose an alternative method to standard QA procedures by producing tissue-equivalent phantoms in the form of patient surface using 3D printing technology in micro MLC based brain and head&neck The outlines of the methodology of the study designed with the aims can be summarized as: (i) Transferring the CT images of selected Head&Neck patients to workstation, (ii) Transporting the CT images to 3D Slicer software and then preparing the model with the form of patient surface in computer environment, (iii) Transporting the parts of models to 3D printer and printing the crusts of the phantom, (iv) Filling the crusts with paraffin wax, (v) Taking the CT images of model and calculating the doses in the treatment planning system (TPS), (vi) Delivering the micro-MLC based IMRT treatment plans in Novalis unit by placing the EBT3 films between the phantom slices, (vii) performing the gama analysis of 2D dose distributions acquired from EBT3 film and TPS. In the gamma analyses of treatment plannings of six head&neck patients, the four sets of criteria were used: 3% dose difference (DD) & 3 mm Distance to Agreement (DTA), 3% DD & 5 mm DTA, 5% DD & 3 mm DTA, and 5% DD & 5 mm DTA. Results In the analysis with 3mm/3% criteria, it was observed that the dose distributions were agreed except for the dose reduction at the edge of the films induced from the deformation. When 5mm/5% criteria were chosen, the agreements between dose distributions of EBT3 film and TPS were found to be 95,7% in average (max. 96,4% and min. 93,4%). The threshold for success was accepted as 90%. Conclusion Consequently, our study showed that the head&neck phantoms produced with 3D printing technology can be used for patient specific QA. By means of new technologies that accelerate the production process, 3D phantom applications including surface contour of patients can be routinely used in radiotherapy facilities. EP-1706 Production of samples with specified CT indices by 3D printing I. Miloichikova 1,2 , Y. Cherepennikov 1 , A. Krasnykh 3 , S. Stuchebrov 3 1 Tomsk Polytechnic University, School of Nuclear Science & Engineering, Tomsk, Russian Federation ; 2 Cancer Research Institute of Tomsk National Research Medical Center of the Russian Academy of Sciences, Radiotherapy Department, Tomsk, Russian Federation ; 3 Tomsk Polytechnic University, Research School of High- Energy Physics, Tomsk, Russian Federation Purpose or Objective This work is aimed at developing a method to produce tissue-equivalent phantoms with predetermined density distribution for the purpose of experimental planning and verification of radiotherapy treatments. The phantoms can be customized to mimic individual anatomical features of each patient. It is advisable to manufacture such phantoms by fused deposition modeling using tomographic data. The phantoms will make it possible to adjust the radiotherapy treatment plans directly on the radiation therapy machine. This will eliminate systematic errors of calculation algorithms. This becomes especially important with high-density implants installed in the region of interest, which do not allow accurate dose calculation due to artifacts in tomographic images. Customized phantoms will eliminate the inaccuracies of traditional experimental verification of radiotherapy plans based on mass-produced phantoms and thereby reduce the adverse effects of radiation therapy. treatment techniques. Material and Methods

Conclusion This study reports a class solution specific OSL-calibration for the large modulated fields encountered in the PART trial. This calibration adds a unique combination of reusability, sub-mm resolution and large FOV to the 2D dosimetry in radiotherapy. EP-1705 Quality assurance of micro-MLC based IMRT plans using patient-specific phantom S. Sunel 1 , M. Yeginer 1 , F. Akyol 1 , F. BILTEKIN 1 , G. Ozyigit 1 1 Hacettepe University, Department of Radiation Oncology, Ankara, Turkey