ESTRO 36 Abstract Book

S794 ESTRO 36 2017 _______________________________________________________________________________________________

in delivering of additional dose of 2,52mGy (4 fr. in protocol A) or 2,92mGy (4 fr. in protocol B) for elective brain irradiation in ALL, 3,55 mGy (5 fr. protocol F) for left sided nephroblastoma 3,4 mGy (5 fr. protocol D) or 3,8mGy (5 fr. protocol C) for right sided nephroblastoma, 17,6 mGy (8 fr. protocol E) for RMS in pelvis and 3,45 mGy (5 fr. protocol G) for LGL.

Conclusion The additional doses of kV CBCT depends on the type of presets used in procedure and number of fractions with IGRT during all treatment. The modified presets enable reducing exposure to irradiation so that IGRT – associated doses seems to be clinically acceptable. However the children’s anthropomorphic phantom is needed to further evaluate exposure of normal healthy tissue to irradiation during colleting the date for IGRT. EP-1500 Application of RayStretch in clinical cases: Heterogeneity corrections in LDR prostate brachytherapy J. Vijande 1 , F. Ballester 1 , J. Perez-calatayud 2 , F. Hueso- González 3 , F. Siebert 4 1 Universitat de Valencia Dep. de Fisica Atomica- Molecular Y Nuclear, Atomic Molecular and Nuclear Physics, Burjassot, Spain 2 University and Polytechnic Hospital La Fe, Physics Section- Radiotherapy Department, Valencia, Spain 3 Target Systemelektronik GmbH, Wuppertal, Germany 4 UK S-H- Campus Kiel- Klinik für Strahlentherapie, Radioonkologie, kiel, Germany Purpose or Objective Tissue heterogeneities and calcifications have significant impact on the dosimetry of low energy brachytherapy (BT). RayStretch is an analytical algorithm developed in our institution to incorporate heterogeneity corrections in LDR prostate brachytherapy. The aim of this work is to study its application in clinical cases by comparing its predictions with the results obtained with TG-43 and Monte Carlo (MC) simulations. Material and Methods A clinical implant (71 I-125 seeds, 15 needles) from a real patient was considered. On this patient, different volumes with calcifications were considered. Its properties were evaluated in three ways by i) the Treatment planning system (TPS) (TG-43), ii) a MC study using the Penelope2009 code, and iii) RayStretch . To analyse the performance of RayStretch , calcifications located in the prostate lobules covering 11% of the total prostate volume and larger calcifications located in the lobules and underneath the urethra for a total occupied volume of 30% were considered. Three mass densities (1.05, 1.20, and 1.35 g/cm 3 ) were explored for the calcifications. Therefore, 6 different scenarios ranging from small low density calcifications to large high density ones have been discussed. Results DVH and D90 results given by RayStretch agree within 1% with the full MC simulations. Although no effort has been done to improve RayStretch numerical performance, its present implementation is able to evaluate a clinical

Conclusion Planning and delivery of IMRT/VMAT has been validated using TG119 report. Local institutional confidence limits were established which can be used as baseline for future patient specific quality assurance. EP-1499 Additional dose of Image Guided Radiation Therapy in Pediatric Patients J. Topczewska-Bruns 1 , T. Filipowski 1 , D. Hempel 1 , B. Pancewicz-Janczuk 2 , R. Chrenowicz 2 , D. Kazberuk 1 , A. Szmigiel-Trzcinska 1 , E. Rozkowska 1 1 Comprehensive Cancer Center, Department of Radiotherapy, Bialystok, Poland 2 Comprehensive Cancer Center, Department of Physics, Bialystok, Poland Purpose or Objective Kilovoltage cone beam computed tomography (kV CBCT) imaging improves the accuracy of radiation therapy. However, an extra radiation dose is delivered to cancer patients. Instead of default scanning protocol used for adults we prepared individual presets for children undergoing radiotherapy in our Department. The aim of the study was to evaluate additional dose delivered to the pediatric patients being treated according to local protocol for IGRT. Material and Methods 10 children, aged 2-6 years with different type of neoplasms were treated in supine position on linear accelerator (Elekta Synergy) equipped with kV CBCT (XVI v.4.2.) The pretreatment position was evaluated according to our protocol on day 1,2,3 and once in a week thereafter. The individual presets for pediatric patients were prepared for different types of neoplasms and localization of the irradiated area For dose calculation delivered by use of kv CBCT the phantom PMMA 20x20x12 and 16x16x16 with CT chamber TM30009 (PTW) with Unidos (PTW) was used. Results The modification of IGRT protocols for children includes changes in the acquisition parameters such as frequency, beam energy, voltage, rotational degree, gantry speed, size of field of view, filter with good quality of images (examples of images from the date obtained by collecting of kV CBCT will be presented on the poster) . The following presets were prepared (Tab.1).The additional dose deliverd to the pediatric patients depends on the number of fractions when the CBCT was performed. Our local protocol for usage of kV CBCT results