ESTRO 36 Abstract Book

S804 ESTRO 36 _______________________________________________________________________________________________

Results All planning goals have been achieved as per TG119 report shown in figure-1. At high dose point measurement mean dose differences averaged over different techniques (IMRT/VMAT) planned with different energies for all test cases was 0.002±0.020, and corresponding confidence limit (mean + 1.96σ i.e. σ stand for standard deviation) was 0.041. At low dose point measurement mean dose averaged over different techniques planned with different energies for all test cases was -0.004±0.021, and corresponding confidence limit was 0.045. For planar dose measurement gamma passing rate averaged over all test cases was 99.40%±0.40 for 3%/3mm criteria and 97.82%±0.13 for 2%/2mm criteria respectively. Present work overall confidence limit (100-mean + 1.96σ i.e. σ stand for standard deviation) for composite planar dose measurement was 1.38(i.e., 98.62% passing) for 3%/3mm and 2.45(i.e., 97.55% passing) for 2%/2mm criteria. Gamma analysis results for a representative measurement are shown in figure-2.

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 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.

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.