ESTRO 2020 Abstract book

S858 ESTRO 2020

and University of Bern, Bern, Switzerland ; 2 Varian Medical Systems Imaging Laboratory GmbH, CH-5405 Dättwil- Switzerland, Dättwil, Switzerland Purpose or Objective Arteriovenous malformation (AVM) is an abnormal connection between arteries and veins, bypassing the capillary system. In order to correctly locate an AVM, typically, a digital subtraction angiography (DSA) is carried out. To use the DSA for target definition in radiosurgery, an accurate image registration between CT and DSA is required. Carrying out a non-invasive, frameless procedure, i.e. having no invasive head frame in place that serves as a fixed coordinate system, registration of the 2D- DSA images with the CT is critical. A new software prototype called Brain Clinic is enabling this frameless procedure. The aim of this work was to evaluate Brain Clinic in terms of targeting accuracy and reliability based on phantom measurements as well as with the aid of patient data. In addition, the user's ability to recognize mismatches between CT and DSA was assessed. Material and Methods Targeting accuracy was determined with a simple cubic, as well as with a more realistic anthropomorphic head phantom. Clearly defined academic targets within the two phantoms were contoured on the CT. The center of mass (COM) coordinates of these reference structures were compared with the COM coordinates of the structures generated within Brain Clinic, based on the 2D-DSA images. A similar approach was used with patient data, where the clinically contoured target served as the reference structure. In order to check if the user is able to recognize registration errors on blended digitally reconstructed radiographs (DRR) and 2D-DSA projection images, a set of different registration errors (translations and rotations) was introduced to the correctly registered CT and 2D-DSA image data sets of three different patients. Each of six different users rated the whole set of registrations within Brain Clinic. Results The target accuracy of the Brain Clinic was found to be below 0.04 cm for the simple cubic phantom and below 0.05 cm for the anthropomorphic head phantom. The mean target accuracy for fifteen patient cases was found to be below 0.3 cm. Artificially introduced registration errors above 1° or 1 mm were detected by the six users and correctly rated as not The method of this study shows, that the prototype is a useful tool that has the potential to fill the gap towards a frameless procedure when treating AVMs with the aid of 2D-DSA images in radiosurgery. The target accuracy of the prototype is similar to other systems, which are already well established in clinical routine. PO-1502 A comparison of photon and proton radiotherapy treatment planning techniques in head and neck cancer D. Church 1 , C. Paterson 2 , S. Currie 1 , P. Houston 1 , R. Valentine 1 1 Beatson West of Scotland Cancer Centre, Radiotherapy Physics Department, Glasgow, United Kingdom ; 2 Beatson West of Scotland Cancer Centre, Radiation Oncology Department, Glasgow, United Kingdom Purpose or Objective Although proton therapy is becoming more widely available it remains a limited and high-cost resource, being used where only the most tangible benefits are anticipated. Although dosimetric advantages of proton therapy have been previously reported for head and neck cancer (HNC), it is unclear if those benefits persist when acceptable. Conclusion

Figure 2. Two cases with the best edvantage for ipsilateral lung and heart All VMAT and HYBRID plans passed through the verification successfully. Conclusion The Eclipse13.7 TPS does not provide the possibility to use the skin flash tool for VMAT plans calculation. So, for breast cancer localizations it’s only possible to calculate either 3D or IMRT plans. The first one is not quite flexible in terms of conformity, the second is difficultin terms of fraction delivery time. Long treatment time is uncomfortable for patient which may lead to shifts of his positioning and inaccuracy of dose delivery. VMAT thus can greatly reduce treatment time. Respiratory Gating system allows to calculate VMAT plans for breast cancer without skin flash tool. But VMAT plans cause much greater coverage of normal tissue with low doses in comparison with 3D. Besides, VMAT optimization is not as flexible as IMRT. HYBRID in conjunction with voluntary breath hold can gives us a flexible treatment planning technique that allows to find an optimum between minimization of dose for critical organs and the complexity of the plan performance and dose delivery. PO-1501 Frameless workflow for radiosurgery of arteriovenous malformations - A new software prototype D. Schmidhalter 1 , D. Henzen 1 , E. Herrmann 1 , W. Volken 1 , P. Mackeprang 1 , E. Ermis 1 , H. Hemmatazad 1 , J. Honegger 2 , B. Haas 2 , M.K. Fix 1 , P. Manser 1 1 Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital- Bern University Hospital-