ESTRO 36 Abstract Book

S974 ESTRO 36 2017 _______________________________________________________________________________________________

(contralateral mucosa, bladder, small bowel, sphincter, prostate) were outlined by the same radiation oncologist on two CT datasets; one with applicator for brachytherapy planning, and the second without applicator for planning for EBT modalities. For the EBT modalities, optimization was performed in such a way to force the exact same CTV coverage as was obtained for each patient treated with HDREBT. Results Comparison of dose distributions in axial, coronal and sagittal planes for one patient are given in Fig.1 (top) for the three modalities investigated. Bottom of the Fig.1 shows comparison between DVH curves for the same patient for CTV and three critical structures (bladder, prostate, and sphincter). Table 1 summarizes averaged (over 10 patients) dose distribution parameters for the three modalities investigated.

Papillon® mobile xray generator is delivering a 50kVp treatment beam that can be used for skin or rectum treatment. A new machine based on the same beam, Papillon+® is being launched to add the opportunity of delivering intra operative breast treatment. OSL principle is to detect light emitted when the luminescence material, which is exposed to radiation, is stimulated with visible light. Associated reader is Microstar ii. Nanodots were irradiated with Papillon® beam treatment to establish calibration curves and to evaluate attenuation. Attenuation was measured by a second nanodot situated under the first one wich is a pessimistic way of determination as both plastic disk infused with Aluminium oxide doped with Carbon Al2O3:C encased in a plastic case. Results Detectors were read after irradiation from 10 to 22.5Gy. No saturation was observed unlikely expected. Results highlight a linear calibration curve with a regression linear coefficient R²=0.9853. Concerning attenuation, results are ranging from 80 to 70% of reference measurements with this methodology. Discussion: While dose used is in treatment range (around 20 Gy), linear calibration can be used which is different from literature results. It may be linked to the evolution made by Landauer concerning the Microstar reader between (Price, Medical Physics 2013) and today. So, OSL can be used at a time to evaluate skin dose but also delivered dose at applicator surface. Attenuation methodology needs to be modified to be more relevant according to our clinical use. Gafchromic films may be used to evaluate surface attenuation. Conclusion OSL nanodots are usable with 50kVp Papillon® beam for breast intraoperative radiotherapy for example. OSL reading is fast and without delay. Attenuation surface of the detector is 0.9x0.9cmxcm that has to be clinically validated before replacing thermoluminescence dosimeters (TLD) classically used. Uncertainties are on the same level as published one concerning TLD (around 17%), they will determined with Papillon+® beam that permits to treat breast in an intraoperative mode. EP-1800 Optical Fibre Luminescence Sensor for Real- time LDR Brachytherapy Dosimetry P. Woulfe 1 , S. O'Keeffe 2 , F.J. Sullivan 3 1 Woulfe Peter, Department of Radiotherapy, Galway, Ireland 2 University of Limerick, Optical Fibre Sensors Research Centre, Limerick, Ireland 3 National University of Ireland Galway, Prostate Cancer Institute, Galway, Ireland Purpose or Objective This paper presents recent advancements in the development of an optical fibre radioluminescence sensor whereby the radiation sensitive scintillator, terbium- doped gadolinium oxysulphide (Gd 2 O 2 S:Tb), is embedded within the core of a 500µm PMMA (Polymethyl methacrylate) plastic optical fibre. The reduced size of the presented optical fibre sensor offers significant advantages for application in brachytherapy. The small dimensions of the sensor (less than 1mm including the outer protective jacket) allows it to be easily guided within existing brachytherapy equipment; for example, within the seed implantation needle for direct tumour dose analysis, in the urinary catheter to monitor urethral dose, or within the biopsy needle holder of the transrectal ultrasound probe to monitor rectal wall dose. Material and Methods The optical fibre sensor, shown in figure 1, is constructed by micromachining a cavity in the 500µm core of a PMMA (polymethyl methacrylate) plastic optical fibre. The

Conclusion From Fig.1 and Table 1 that both EBT modalities provide very conformal dose distribution to the target while providing generally better spearing of surrounding critical structures except for the contralateral rectal wall. The main advantage of brachytherapy is that there is no need for additional PTV margin as the source moves together with the rectum. However, our results suggest that even the addition of PTV margins to sophisticated EBT modalities can produce comparable (if not better) dose distributions to brachytherapy plans. Although, all the EBT modalities possess the image guided radiotherapy (IGRT) systems that allow repositioning of the patient (hence target) just before commencing the treatment fraction, it is difficult to ascertain the impact of daily intra-treatment rectal motility and gas interference on the CTV in this study. The superior dose within HRCTV is best observed with HDRBT and likely the most important factor for achieving complete tumor response in the context of organ preservation [Appelt et al, Int J Rad Oncol Biol Phys 2013; 85: 74-80]. EP-1799 Feasibility study of in vivo dosimetry with optically stimulated dosimeters for 50kVp Papillon® beam C. Dejean 1 , A. Mana 1 , M. Gauthier 1 , J. Feuillade 1 , C. Colnard 1 , J. Gérard 1 1 Centre Antoine Lacassagne, Academic Physics, Nice, France Purpose or Objective to evaluate optically stimulated luminescence dosimeters (OSL, nanodot Landauer ™) to be used for in vivo dosimetry with 50kVp beam. Material and Methods