ESTRO 36 Abstract Book

S409 ESTRO 36 2017 _______________________________________________________________________________________________

Results The new components of the robotic phantom are presented in figure 1. Major technological advancements with respect to the evaluation model are: • Robot: A novel kinematic structure has been found, which reduces the number of joints and increases stiffness of the mechanics. A fatigue endurable mechanical construction has been created. Rapid exchange of the Target core and inclusion of tethered measurement devices are now possible via the hollow end effector.

environments, optionally containing radioactive tracers, are supported. A unique feature of the phantom is its combination of the described high flexibility with practical feasibility, efficiency and robustness. Next, real time robot control capabilities will be extended and clinical long term studies will be performed. PO-0780 Feasibility study of beam monitoring system using AFCRS for proton pencil beam J.M. Son 1 , M.Y. KIM 2 , M.G. Yoon 3 , D.H. Shin 1 1 National Cancer Center, Proton therapy Center, Goyang-si- Gyeonggi-do, Korea Republic of 2 Dongnam Inst. Of Radiological & Medical Sciences, Research Center, Busan, Korea Republic of 3 Korea University, Bio-convergence engineering, Seoul, Korea Republic of Purpose or Objective PBS, recently developed, scans a tumor with very precise beam of protons that’s accurate within millimeters, sparing the healthy surrounding tissues. But it is able to harmful rather than conventional radiotherapy if the beam is not accurately irradiated as planned. It is very important to measure beam width and spot center of the proton pencil beam for the accurate delivery of dose to the target volume with a good conformity. We have developed the beam monitoring system using Array of Fiber-Optic Cerenkov Radiation Sensor (AFCRS), and conducted feasibility study for proton pencil beam. Material and Methods We have developed a fine segmented detector array to monitor PBS. A prototype beam monitor system using AFCRS has been developed for real-time display of the pencil beam status during the PBS mode operation. The x- y monitoring system with 128 channel readout is mounted to the snout for the in-situ real time monitoring. Beam widths and spot centers of various energies are measured. Two dimensional Gaussian fit is used to analyze the beam width and the spot center. The ability of this system to evaluate Lynx system (Scintillator-based sensor with CCD camera) and EBT3 for PBS was compared. Results The measured Gaussian widths using AFCRS changes from 13 to 5 mm for the beam energies from 100 to 226 MeV. The beam widths of PBS using the AFCRS are well matched with the data acquired by a Lynx system and EBT 3 film. In addition, spot centers for 226 Mev PBS beams are also well matched with RTP system. Conclusion The dosimetric performance of the newly developed system based on AFCRS was comparable to that of the Lynx system and EBT3 film. Not only measuring the spot profile but also monitoring dose map by accumulating each spot measurement will be available. PO-0781 A characterisation of EBT3 Gafchromic film for relative and absolute dosimetry I. Billas 1 , H. Bouchard 2 , A. Subiel 1 , I. Silvestre 1 , S. Duane 1 1 National Physical Laboratory, Radiation Dosimetry, Middlesex, United Kingdom 2 Université de Montréal, Département de physique, Montréal, Canada Purpose or Objective The aim of this work is to investigate the variation in dose response of Gafchromic EBT-3 film within each film and across films from different boxes and lots. In this way the uncertainty of relative and absolute dosimetry using EBT- 3 film is quantified and its potential for use in small field and MRI-guided radiotherapy is better understood. Material and Methods Sheets of Gafchromic EBT-3 film were uniformly irradiated in a cobalt-60 beam in increments of 1 Gy up to a cumulative dose of 10 Gy. Films were scanned repeatedly before the first irradiation and after each step. Software for image processing and analysis was implemented in

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Modularization: Body and Target can now be assembled manually and rapidly while ensuring an absolute positioning accuracy of < 0.1 mm. Third party phantom structures can be incorporated and accounted for in a customizable collision control. Software: A control software release has been developed featuring extended functions, simplified usage and platform independence.

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Figure 2 shows the phantom in a clinical setup. A static and a respiratory gated CT were performed. Respiration surrogates were acquired using the C-Rad Sentinel System. Furthermore, a Cone Beam CT mounted at a linear accelerator was obtained.

Figure 1: Structure of the robotic phantom

Figure 2: Results of medical imaging Conclusion

First applications of the phantom under clinical conditions and purposes revealed feasible physical properties, functional range and applicability. The platform technology of the phantom has reached prototype maturity and can be flexibly adapted to a broad range of clinical scenarios. For example, both little and high complexity of human equivalent structure and motion, both film and ion chamber dosimetry, both air and fluidic