ESTRO 36 Abstract Book

S407 ESTRO 36 2017 _______________________________________________________________________________________________

PO-0776 Thermoluminescence Characteristics of Fabricated Ge Doped Optical Fibre for Radiotherapy Dosimetry M.S. Ahmad Fadzil 1 , N. Tamchek 2 , N.M. Ung 3 , A. Ariffin 4 , N. Abdullah 5 , D.A. Bradley 6 , N. Mohd Noor 1 1 Universiti Putra Malaysia, Department of Imaging- Faculty of Medicine and Health Sciences, Serdang, Malaysia 2 Universiti Putra Malaysia, Department of Physics- Faculty of Science, Serdang, Malaysia 3 University of Malaya, Clinical Oncology Unit- Faculty of Medicine, Kuala Lumpur, Malaysia 4 University of Malaya, Department of Physics- Faculty of Science, Kuala Lumpur, Malaysia 5 Malaysia Nuclear Agency, Medical Physics Group, Kajang, Malaysia 6 University of Surrey, Department of Physics, Guildford, United Kingdom Purpose or Objective The dosimetry characteristics of the fabricated Germanium doped cylindrical fibre (CF) and flat fibres (FF) were evaluated including linearity, repeatability, energy dependence, dose rate dependence, angular dependence and fading. The TL kinetic parameters of Ge-doped CF and FF have been investigated using the computerized glow curve deconvolution analysis. Material and Methods A screening process was carried out for the optical fibres with 6 MV photon beam. Optical fibres with sensitivity out of ±5% mean sensitivity value were discarded in order to ensure the selected dosimeters have constant response. The dosimetry characteristics tests were performed using 6 MV and 10 MV photon beams. The dosimeters were irradiated with doses ranging from 1 Gy to 3 Gy with several dose rates (100 MU/min up to 500 MU/min). Fabricated perspex phantoms were used to study the angular dependency of the optical fibres. Fading rate was studied for 55 days post irradiation. The glow curves were analyzed with a curve fitting computer program known as WinGCF. The glow curves were deconvoluted into five individual peaks in order to figure out the kinetic parameters such as the maximum peak temperature ( T max ), peak integral ( PI ), activation energy ( E a ) and frequency factor. Results The screening result revealed that the coefficient of variation was observed to be less than ±10% for CF and FF. Both CF and FF were found to be linear with r 2 more than 0.99 over the entire dose range explored for both 6 MV and 10 MV photon beams. These fibres provide consistent reading within ±5% over five repeated measurements. The signal lost was higher in FF (57%) compare to CF (38%) after 55 days of irradiation. Both fibres also offer dose rate- and angular independence. The glow curve for both CF and FF consist of 5 individual glow peaks. The peak height increased with increasing irradiation dose. The T max of the glow peaks (P1 to P5) is consistent over the dose range used . Peak 1 has the lowest E a which lies between 0.544 to 0.636 eV and 0.632 to 0.720 eV for CF and FF respectively, indicating the shallow electron traps. The results also revealed that the PI for both of the fibres will increase as the dose increase. The Ge-doped CF and FF demonstrated a constant glow curves shape with increasing dose. As the dose increases, area under the glow curve increases, suggesting an increasing number of electrons released from its traps. Conclusion CF demonstrated greater TL signal compared to FF. In order to employ these optical fibres in absorbed dose measurement, correction factors for energy dependence and fading should be applied. The Ge-doped CF and FF demonstrated the second-order kinetic model to the high temperature half of the curve is slightly broader than the low temperature half which suggest the possibility of

strong electron retrapping. The evaluation on Ge doped optical fibres showed a highly favourable TL characteristics exhibited by CF and FF indicate a great potential in radiotherapy postal dose audit. PO-0777 Importance of dosimetry formalism for cells irradiation on a SARRP and consequences for RBE M. Dos Santos 1 , V. Paget 2 , M. Ben Kacem 2 , F. Trompier 3 , M. Benadjaoud 1 , A. François 2 , O. Guipaud 2 , M. Benderitter 1 , F. Milliat 2 1 Institute for Radiobiological Protection and Nuclear Safety IRSN, Department of Radiobiology and Epidemiology SRBE, Fontenay-aux-Roses- Paris, France 2 Institute for Radiobiological Protection and Nuclear Safety IRSN, Department of Radiobiology and Epidemiology SRBE- Research on Radiobiology and Radiopathology Laboratory L3R, Fontenay-aux-Roses- Paris, France 3 Institute for Radiobiological Protection and Nuclear Safety IRSN, Department of external dosimetry SDE- Ionizing Radiation Dosimetry Laboratory LDRI, Fontenay- aux-Roses- Paris, France Purpose or Objective Since last three decades, the importance of the dosimetry in radiobiology studies and the standardization of the dosimetry protocols have been highlighted. Nevertheless, most of time, it is very difficult to reproduce experiments described on literature due to a lack of details in the description of dosimetry protocols. As the main objective of radiobiology is to establish links between doses and the radiations-induced biological effects, well-defined dosimetry protocols appear to be a crucial point within the determination of experimental protocols. In this context, detailed dosimetry protocols for cells irradiation have been implemented on the Small Animal Radiation Research Platform (SARRP). To support the importance of all parameters described on dosimetry protocols, manual protocol changes were performed by modifying the cell growth medium volume and/or the additional filtration for an irradiation at 80 kV. Impacts of modifications of the physical dose induced by these errors/protocols changes were studied on RBE (Relative Biological Effectiveness) using the survival clonogenic assay. Material and Methods In first, all parameters of the configuration setup (HT, HVL …) have to be defined. Then, measurements of absolute dosimetry with ionization chamber calibrated in air Kerma free in air condition, converted then in water kerma free in air, and relative dosimetry with EBT3 radiochromic films were performed to determine dose rate and evaluate the attenuation due to the cell growth medium in each containers used for cells irr adiation. In order to evaluate the influence of the modific ation of parameters like cell medium volume (1 or 9 mL I nstead of 3 mL as the reference condition) and/or the additional filtration, 6 plate wells containing EBT3 films with water were used to determine the impact on the physical dose at 80 kV. Then, experiments with rigorously the same irradiation conditions were performed by replacing EBT3 films by HUVECs. The biological response of HUVECs was assessed by using clonogenic assay. Results Characterization of the beam quality index in the range of 30 to 220 kV for copper and aluminum filtrations and the homogeneity of the field size have been measured. Then, impact of the cell culture volume and filtration have been evaluated thanks to measurements with EBT3 films and show a variation between 1 to 8% with the copper filtration and 8 to 40% with aluminum filtration compared to each reference condition. HUVECs cells irradiated in the same conditions showed significant differences in cell survival fraction, perfectly corroborating the dosimetric changes observed on physical dose.