ESTRO 38 Abstract book

S1207 ESTRO 38

plan was recalculated on the phantom CT images with SEMAR algorithm. Dose calculation results were compared between CT numbers in metal regions replaced with that for the density of Titanium alloy and 2) no correction. An ion chamber was placed at the phantom center for dose comparison to TPS calculation. A film was placed inside a water phantom with a metal object and beams were delivered. Gamma analysis was performed between the film measurements and the TPS dose calculation. Results The dose difference of the measured those and the calculation using SEMAR without no correction are shown in Table.1. The avoidance VMAT did not show the metal effects in all the plans. The density correction improves the dose calculation. Differences in dose distributions with and without the metal was mainly observed in low dose regions due to back scattering from the metal object. Conclusion We observed a significant impact of a metal object on dose distributions in VMAT when a single full arc beam was delivered. However VMAT beams with the avoidance angles id not suffer from the metal effect. The CT with metal artifact reduction improves the dose calculation in IMRT. EP-2188 The risk of CIEDs damage by photon beams, define by neutron activation products of CIED materials W. Szyszka 1 , E. Konstanty 2 , K. Brudecki 3 1 Greater Poland Cancer Center, Departement of Radiotherapy II, Poznań, Poland ; 2 Greater Poland Cancer Center, Departement of Medical Physics, Poznań, Poland; 3 Kraków, Poland Purpose or Objective Epithermal or thermal neutron derived from photon beam radiation with energy above 10 MV could react with nuclei of the CIEDs materials. Threshold energies do not apply to (n; γ) reactions. The study performance based on the risk of the pacemaker or cardioverter-defibrillator damage in a linear accelerator environment analyzing isotopes of elements of devices subjected to irradiation will depend only on the photon beam energy used during RT and the ensuing neutron contamination. The study is focused on understanding the mechanism causing devices malfunctions. Material and Methods The study was performed based on the analysis of high- resolution gamma spectroscopy. Isotopes spectra allow establishing the occurrence of the reaction, and simultaneously determine the portion of emitted energy by detecting the type of the isotope and neutron contamination of the photon beam in linear medical accelerator environment. The study conducted for (i) 6 MV, (ii) 10MV, (iii) 15MV, (iv) 20 MV photon energy for 4 CIED distances relative to the radiation beam - 1) directly in the radiation beam, 2) 10 cm 3) 40 cm and 4) 100 cm from the edge of the radiation field. Each CIED received a dose of 2 Gy. The spectra of device material isotopes were detected using High Purity Germanium detector (HPGe). Results For the samples of CIEDs, which has irradiated with high- energy photon beam ( <15 MV) the different spectra of isotopes were observed. ccurrence in samples spectra of long-lived isotopes on the energy of 350-360 keV confirmed neutron activation reaction.

Conclusion The CIEDs function in patients irradiated with above 10 MV photons should be avoided or if necessary closely monitored, especially in patients subject the increasing number of neutrons in high energies beams, the probability of malfunction increase with the energy of the beam, causing irreversible life-treating failures of the device. The appearance of long-lived isotopes explains the occurrence of CIEDs damages even after a long time from radiotherapy. Understanding the exact mechanism and all the factors of arising malfunctions of CIED is extremely important in consideration of the ever-increasing percentage of patients with CIEDs undergoing radiotherapy. EP-2189 Compare OARs dose in postoperative high-risk prostate cancer patients using IMRT and VMAC technique Y. Chen 1 , L. Chou 1 , T. Wang 2 , Y. Liu 1 1 Taipei Veterans General Hospital, Department of Oncology, Taipei City, Taiwan; 2 China Medical University Hospital, Division of Radiation Oncology, Taichung City, Taiwan Purpose or Objective For prostate cancer patients post radical prostectomy with high risk features, post-operative radiotherapy improves biochemical progression-free survival at the cost of increased urinary and intestinal toxicities. Comparing to 3D conformal radiotherapy, step-and-shoot intensity- modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT) both provide highly conformal dose distribution with good sparing of normal tissues in definitive setting. However, no comparison is done for the two techniques in post-operative radiotherapy setting. Material and Methods Seventy-five consecutive post-operative prostate cancer patients were selected retrospectively for this dosimetric comparison study. nineteen patient received IMRT and 60 patient received VMAT radiotherapy using the Eclipse™ treatment planning system (Varian Medical Systems). Planning target coverage, monitor units (MU), dose to bladder and rectum were compared across techniques. Results Overall, dose to the prostate bed, expressed as mean ±standard deviation, was 74.7± 1.1 (Gy). PTV coverage and total MU were 97.65±1.47 %and 1090.5±279.5 MUs for VMAT and 97.05±1.49 % and 913.3±441.1 MU for IMRT technique. For rectum, mean dose, V40, V45, V50, V55, V60, V65 were 46.2/46.75 Gy (p = 0.78), 35.4/35.6 %(p = 0.93), 27.2/26.9 (p = 0.92), 20.3/19.9 (p = 0.83), 14.2/13.4 (p = 0.68), 8.0/5.6 (p = 0.15), 1.4/1.7 (p = 0.77) % in VMAT and IMRT technique. For bladder, mean dose, V40, V45, V50, V55, V60, V65 were 63.1 /49.2 Gy (p = 0.04), 54.9/40.5 (p = 0.01), 45.9/32.6 (p = 0.02), 38.5/26.0 (p = 0.02), 32.0/20.5 (p = 0.02), 25.7/14.1 (p = 0.01), 7.4/4.2 (p = 0.17) % in VMAT and IMRT technique.