ESTRO 36 Abstract Book

S520 ESTRO 36 2017 _______________________________________________________________________________________________

Material and Methods The kinetic M 1

funduscopic images MRI can be used to better assess the delivered doses to the target and the organs-at-risk (OAR). The main goal of this feasibility study is to demonstrate that fundus mapping and post implantation MR imaging can be incorporated into the treatment planning workflow of 106 Ru plaque brachytherapy. Material and Methods Patients were scanned in a 0.35 T MR scanner (Magnetom C! Siemens, Germany) after 106 Ru eye plaque implantation. To achieve a good normal tissue contrast for tumor delineation and organ-at-risk (OAR) segmentation a fast low angle shot (FLASH) T1 weighted sequence was utilized (TR = 15 ms, flip-angles = 25°). A second FLASH MRI scan with lower repetition times (TR = 11.2 ms) and flip-angles (20°) was applied in order to display the plaque as a well- defined void with minimal distortion artifacts at the cost of lower signal to noise ratio and less soft tissue contrast. Based on the MRI the resizable 3D eye model of a newly developed treatment planning software (described in detail in [1]) was adapted to the individual patient anatomy in terms of size and plaque position. Furthermore, the funduscopy image was projected onto the retina of the digital 3D eye model. Results The presented method using two MR sequences yielded 3D image sets that allowed segmenting both the anatomical structures and the 106-Ru plaque. The funduscopy image on the other hand is the optimal modality for tumor segmentation. By combination the 3D eye model can be adapted to match the individual patient and thus allow for individual treatment planning and dose calculation (based on MR anatomy) where the post-implantation imaging accounts for the actual position of the plaque with respect to the target and critical structures. This way irradiation times can be calculated which guarantee full tumor coverage. Moreover, the workflow can be applied for treatment plan optimization strategies where plaques are shifted in order to reduce doses to OARs. Conclusion In this feasibility study it was shown that MRI in combination with funduscopy can be used to optimize brachytherapy with 106 Ru plaques. The additional spatial information on plaque position relative to critical structures, tumor geometry as well as position can be used for more precise dose calculations and therefore improved treatment planning. References: [1] G. Heilemann et al. Treatment plan optimization and robustness of 106 Ru eye plaque brachytherapy using a novel software tool. Radiotherapy and Oncology. (in revision) PO-0948 Role of HDR Intraluminal Brachytherapy in carcinoma Esophagus: An institutional experience. P.B. Kainthaje 1 , P. Gaur 1 , A. Malavat 1 , R. Paliwal 1 , V. Sehra 1 1 Dr. Sampurnanand Medical College, Department of Radiotherapy, Jodhpur, India Purpose or Objective To study the profile of patients of Carcinoma Esophagus treated with Intraluminal Brachytherapy (ILBT), the outcome of the treatment in terms of response assessment, toxicity and survival. Material and Methods The study period was between January 2014 and June 2015, with 25 patients of carcinoma esophagus middle third, treated with ILBT either as part of definitive Radiotherapy or as part of palliative Radiotherapy. The patients with unifocal disease ≤10cm in length and with no recorded intra-abdominal or distant metastases received definitive Radiotherapy with 44Gy/22Fr through EBRT with Poster: Brachytherapy: Miscellaneous

model, is based on the spherical harmonic expansion of the distribution function, solution of the linear Boltzmann equation. The first two angular moments equations, combined with the Continuous Slowing Down Approximation, are closed using the Boltzmann's principle of entropy maximization. The algorithm computes at the same time all primary and secondary particles created by the interactions of the beam with the medium. Thanks to the implementation of the interaction cross sections for electrons and photons in the energy range from 1keV up to 100 MeV, the algorithm can simulate different treatment techniques such as the external radiotherapy, brachytherapy or intra-operative radiation therapy. As a first validation step, a large number of heterogeneity shapes has been defined for various complex numerical phantoms both for electron and photon monoenergetic sources. Dose profiles at different positions have been measured in water phantoms including inhomogeneity of bone ( ρ = 1.85 g/cm 3 ), lung ( ρ = 0.3 g/cm 3 ) and air ( ρ = 10 -3 g/cm 3 ). Secondly, taking as reference the Carleton Laboratory for Radiotherapy Physics Database, different radioactive seeds have been implemented in the code. Moreover, several simulations based on CT scan of prostate cancer have been performed. The M 1 model is validated with a comparison with a standard, accurate but time consuming, statistical simulation tools as PENELOPE. Results The M1 code is capable of calculating 3D dose distribution with 1mm 3 voxels without statistical uncertainties in few seconds instead of several minutes as PENELOPE. Thanks to its capability to take into account the presence of inhomogeneities and strong density gradients, the dose distributions significantly differ from those calculated with the TG-43 approximations. More in detail: inter-seed attenuation is treated, the real chemical composition of the different tissues can be taken into account and the effects of patient dimensions are considered. Conclusion In the comparison with the MC results the excellent accuracy of the M 1 model is demonstrated. In general, M 1 , as the MC codes, overcomes the approximations that are formalised in TG-43 in order to decrease the complexity of the calculations. Thanks to its reduced computational time and its accuracy M 1 is a promising candidate to become a real-time decision support tool for brachytherapists. PO-0947 Image-guided brachytherapy with 106Ru eye plaques for uveal melanomas using post implantation MRI G. Heilemann 1 , N. Nesvacil 2 , M. Blaickner 3 , L. Fetty 1 , R. Dunavoelgyi 4 , D. Georg 2 1 Medical University of Vienna/ AKH Vienna, Department for Radiotherapy, Vienna, Austria 2 Medical University of Vienna/ AKH Vienna, Department for Radiotherapy/ Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria 3 Austrian Institute of Technology GmbH, Health and Environment Department Biomedical Systems, Vienna, Austria 4 Medical University of Vienna/ AKH Vienna, Department for Ophthalmology and Optometry, Vienna, Austria Purpose or Objective In radiation oncology magnetic-resonance imaging (MRI) is an important modality for tissue characterization, target delineation and allows image-guidance due to its high soft tissue contrast as a tool for better cancer treatment. In 106 Ru-brachytherapy of uveal melanomas MRI is mainly used for pre-treatment planning scans to assess tumor size and location. However, post-implantation MR scans yield additional information on the plaque position in relation to the target volume and critical structures. Together with