ESTRO 36 Abstract Book

S608 ESTRO 36 _______________________________________________________________________________________________

patient because the MRI showed no enhancement. Since FET-PET enables differentiation between vital tumor and therapeutic associated changes, we compared RecTV PET to GTV MRI and GTV PET . Median IV of GTV PET /RecTV PET (4.1 ml, range: 0-20.8 ml) was larger than GTV MRI /RecTV PET (2.8 ml, range: 0-18.1 ml). Accordingly, the median CI showed higher conformity with 0.19 (range: 0-0.63) and 0.07 (range: 0-0.48), respectively. We calculated median ratio of IV GTV PET /RecTV PET to GTV PET (44.8%, range: 0-100%) and the median ratio of IV GTV MRI /RecTV PET to GTV MRI (32.2%, range: 0-96.6%) to show that the proportion of GTV PET developing tumor recurrence tended to be higher than the proportion of GTV MRI . Conclusion The patterns of recurrence were similar in MRI and FET- PET concerning localization related to PTV. Only one patient showed out-field recurrence, all others developed in-field/field-border recurrence. Therefore, it is indicated that current margin concepts are a safe way to define PTV. However, the GTV PET displays remaining tumor more reliable, and it seems to offer a better prediction of the localization of later tumor growth than the GTV MRI . This leads to the assumption that dose escalation in the GTV PET area might be a worthy subject for future trials. EP-1111 Cyber knife for Idiopathic Trigeminal Neuralgia – Novel technique to reduce brainstem dose P.S. Sridhar 1 , N. Madhusudhan 1 , K. Roopesh 1 , H. Madhusudhan 2 , R. Satish 3 , G. Swaroop 3 , A. Jerrin 1 , A. Pichandi 1 , J. Vijaykumar 1 , M. Praveen kumar 1 , S. Shivkumar 4 , M. Arunakumari 1 , G. Monica 5 , B. Ramesh 1 , K. Gurunath 1 , B. Ajai kumar 1 1 Health Care Global Enterprises Ltd, Cyberknife- Radiation oncology, Bangalore, India 2 Sagar Hospital, Neurosurgery, Bangalore, India 3 Sakra hospital, Neurosurgery, Bangalore, India 4 Health Care Global Enterprises Ltd, Radiology, Bangalore, India 5 Health Care Global Enterprises Ltd, Aneasthesia, Bangalore, India Purpose or Objective Idiopathic trigeminal neuralgia is a functional disorder and most painful condition known to mankind. Diagnosis is always clinical, no radiological and functional scans will be helpful. Medical management and Microvascular decompression of aberrant vessel, Radiofrequency ablation, alcohol injection are used extensively with minimal response. Stereotactic radiosurgery is becoming popular with good results. Most commonly used is targeting the trigeminal nerve at its root entry zone. Dose schedule varies from 66-86Gy single fraction. Brainstem dose is still a concern which is not addressed Primary objective is to assess the safety and efficacy of treating Idiopathic Trigeminal Neuralgia by Stereotactic Robotic Radiosurgery in Meckels cave area to reduce brain stem dose. Material and Methods 12 patents of Idiopathic Trigeminal Neuralgia treated with Stereotactic Robotic Radiosurgery (Cyberknife) between Jan 2010 to Dec 2015.6 were female,6 male. Age range 34- 75,mean age 46 .6 were on right side,6 left side. Duration of symptoms before the treatment range from 2 to 25 years. All patients had one or other form of standard treatment with unsatisfactory response. All patent undergo MRI based Cyberknife planning. The affected side trigeminal nerve is identified ,The part of nerve in Meckels cave and 3 branches are marked ,brain stem and other critical structures are contoured . GTV ranged 260-824mm3,mean 500mm3, Dose prescription ranged from 70-80% mean 76% and peripheral dose ranged from 56Gy-70Gy,maximum dose 70Gy to 80Gy

mean 75.4Gy.Brain stem maximum dose ranged between 7.6Gy to 18.3Gy mean 12.7Gy. Results All 12 patients had complete response at 6 weeks,2 patent had recurrence of pain at 8 and 10 months ,10 patents has altered sensation on treated trigeminal area in the form of loss of sensation,hyperasthesia.None of them had brainstem symptoms. Conclusion Stereotactic Robotic Radiosurgery (Cyberknife) is 76Gy single fraction is safe and effective in Idiopathic Trigeminal Neuralgia .Treating trigeminal nerve in Meckels cave area and 3 branches will give good pain control with less dose to brainstem. EP-1112 Dosimetric evaluation in tri-cobalt60 viewray system for hypofractionated imrt in brain metastases M. Ferro 1 , E. Placidi 2 , S. Chiesa 1 , F. Cellini 1 , M. Massaccesi 1 , G.C. Mattiucci 1 , V. Frascino 1 , R. Canna 3 , C. Masciocchi 4 , L. Azario 5 , V. Valentini 6 , M. Balducci 6 1 Fondazione Policlinico A. Gemelli, Gemelli ART - Radiation Oncology, Rome, Italy 2 Fondazione Policlinico A. Gemelli, UOC Fisica Sanitaria - Gemelli ART - Radiation Oncology, Rome, Italy 3 Fondazione Policlinico A. Gemelli, TSRM - Gemelli ART - Radiation Oncology, Rome, Italy 4 Fondazione Policlinico A. Gemelli, KBO Labs - Gemelli ART - Radiation Oncology, Rome, Italy 5 Università Cattolica del Sacro Cuore, Institute of Physics- UOC Fisica Sanitaria- Gemelli ART - Radiation Oncology, Rome, Italy 6 Università Cattolica del Sacro Cuore, Gemelli ART - Radiation Oncology, Rome, Italy Purpose or Objective Meridian is a system equipped with 3 rotating 60Co sources for IMRT and magnetic resonance imaging (MRI) for real- time vision of target volume (TV). The aim of this in silico study was to evaluate the dosimetric impact of this technology when hypofractionated IMRT is used to treat Treatment plans were performed with a monoisocentric IMRT technique using different number of beams. Margin to PTV was 3 millimeters as normally used for LINAC plans. Total dose prescribed according to ICRU 83 was 25.5 Gy in 3 fractions. TV coverage, Paddick dose conformity (CI), homogeneity (HI), dose to organ at risk (OAR) and to normal brain were analyzed for all plans. Results Sixteen brain metastases were evaluated and 80 plans were analyzed. No significative statistical difference was observed in HI when beams number was increased (p > 0.5). The CI did not change between different beams arrangements. No significant statistical difference was observed when beam's number was correlated with TV or sparing normal tissues. Conclusion IMRT plans using the tri-60Co ViewRay System are feasible according to ICRU 83. The real-time vision of target volume by MR could allow to reduce the PTV margin saving the normal tissue. An ongoing study is comparing ViewRay plans with 3 millimeters to PTV with plans in which no margin is added and PTV is the equal to GTV. P-1113 Helical Tomotherapy and altered fractionation in the treatment of Glioblastoma C. Caruso 1 , R. Barbara 1 , S. Gomellini 1 , A.D. Andrulli 1 , A. Caccavari 2 , M. Moreschi 3 , U. De Paula 1 1 Complesso Ospedaliero San Giovanni Addolorata, Radioterapia, Roma, Italy brain metastases (BM). Material and Methods