ESTRO 36 Abstract Book

S972 ESTRO 36 2017 _______________________________________________________________________________________________

in the SagiPlan® TPS in order to perform the applicator reconstruction based on the markers and pre-defined template, based on the 3D applicator model, loaded in SagiPlan®. The presented technique could be expanded to any rigid applicator and other image modalities, under condition of the adequate selection of the markers. It is necessary to mention, that positioning of the accessory attachments on the applicator is very easy and does not affect integrity or other characteristics of the product.

For this study, 38 patients dose plans were calculated with the reference dosimetry using the TG43 and a manual optimization. A dosimétric comparaison for each plans was done with the dose calculation algorithm based on the TG186 and the optimisation algorithm HIPO. Finally, to study the conformity and consistency of the different algorithms, both COnformity INdex (COIN) and Homogeneity Index (HI) were calculated for the different cases. Results Considering the comparison between the TG43 and TG186 and the most relevant criteria, dosimetric data does not show a significant difference for gynecological, anal canal, prostate, H&N and skin plans. But results for prostate and H&N plans were relevant: a decrease of 13.75% for V50Gy with the TG186 is obtained. This difference is accentuated with the high dose. For the lead, an increase of 21.6% for D25% with the TG186 is obtained (Fig 1). Regarding the optimization algorithms HIPO/manual and considering the most relevant criteria, there is no significant difference on the target volumes on the D90%. For the two optimizations, the mean value respects the dosimetric constraints for the 5 cases of treatment (difference of 4.3% for the gynecological case, 4.4% for the anal canal case, 1.2% for the prostate case, 0.7% for ENT case, and 6.4% for skin case). Furthermore, the inverse optimization algorithm HIPO shows less fluctuation with respect to manual optimization and results are more homogeneous. The value obtained for the COIN and HI for HIPO were higher than those obtained for a manual optimization in the 5 cases especially for the prostate case (Table 1). Conclusion The difference between the TG43 and the TG186 is for most clinical cases not significant for target volumes and OARs except sources in the case of the prostate, as well as lead in cases of H&N. The use of HIPO optimization algorithm has shown a real advantage in the robustness of calculation. Moreover, HIPO enables a reduced dwell time by position, so a total treatment time shorter than the ones obtained with manual optimization. EP-1797 Dosimetric characterization of MOSFET detectors for Ir-192 and feasibility for in vivo dosimetry. R. Fabregat Borrás 1 , S. Ruiz-Arrebola 1 , M. Fernández Montes 1 , E. Rodríguez Serafín 1 , J.T. Anchuelo Latorre 2 , M.T. Pacheco Baldor 1 , J.A. Vázquez Rodríguez 1 , M.M. Fernández Macho 1 , D. Guirado 3 , P.J. Prada 2 1 Hospital Universitario Marqués de Valdecilla, Radiophysics, Santander, Spain 2 Hospital Universitario Marqués de Valdecilla, Radiation Oncology, Santander, Spain 3 Hospital Universitario San Cecilio, Radiophysics, Granada, Spain Purpose or Objective There is a recognized interest in developing in vivo dosimetry (IVD) as an effective method of independent treatment verification for HDR BT treatments [1]. The purpose of current study was to perform a dosimetric characterization of MOSFET TN-502RDM from Best Medical Canada in order to optimize their use in HDR BT treatments delivered with the Ir-192 source contained in Flexitron afterloader (Nucletron-Elekta).

Conclusion We designed several accessory attachments for the markers to be placed on Vienna applicator, which allow easy, fast and precise reconstruction. This technique can be expanded for other applicator types. Additionally it permits to resolve the practical issue of the marker availability for the reconstruction in MRI . EP-1796 Dosimetric comparison between TG43/TG186 algorithms and manual/inverse optimization in brachytherapy T. Brun 1 , E. Torfeh 1 1 Institut Universitaire du Cancer Toulouse - Oncopole, DIPM, Toulouse, France Purpose or Objective For brachytherapy planning treatment, different types of algorithms are used for calculate and optimize the dose distribution. In Toulouse, reference treatment plans are calculated with the software Oncentra Brachy which is based on the formalism TASK GROUP 43 (TG43) and manual optimization. The aim of this project is to compare two algorithms dose calculation: TG43, which does not take into account the heterogeneities vs. TG186, which takes into account the heterogeneities. This comparison was realized for gynecological, anal canal, prostate, H&N and skin treatments in order to strengthen clinical practices on the prescribed dose. Finally, in order to improve the dosimetric quality and harmonize clinical practices, a second study was done to evaluate the difference between a manual optimization and an automatic inverse optimization algorithm with Hybrid Inverse Planning Optimization (HIPO). Material and Methods