ESTRO 38 Abstract book

S683 ESTRO 38

for PFS analysis, KPS (p<0,001), surgery (p:0,005), MGMT (p:0,001) and PE/GTV ratio (p:0,005). At multivariate analysis of OS, the only significant parameters were MGMT (p:0,011), KPS (p:0,008) and PE/GTV (p:0,034). Conclusion Our results suggest that the PE/GTV ratio, together with the known clinical parameters, could play a role in the prognosis of glioblastoma patients. EP-1240 Hypofractionated radiotherapy for non resectable glioblastoma multiforme patients I. Nieto Regueira 1 , O. Virginia 1 , M. Victor 1 1 Hospital Meixoeiro VIGO, Radiation Oncology, Vigo, Spain Purpose or Objective Gliobalstoma multiforme is one of the worst prognosis tumor of the central nervous system. The first step in the treatment is complete surgical resection and it is a good medium and long term prognosis factor when performed. In fact, when complete surgical resection is not possible, disease free survival and global survival decline significantly. Radiotherapy is the other treatment that improves survival and local control. 1- year overall survival is observed in operated and irradiated patients and decreases to 3-4 months in non-resectable patients. Temozolomide, as concomitant treatment to radiotherapy, increases an average of 3 months the survival.Standard radiotherapy dose is 60 Gy in 2 Gy /fraction. In the past higher doses have not shown a benefit in trials. Brachytherapy or radiosurgery have not shown any benefict either. The aim of this prospective trial is to evaluate altered fractionation in these patients. Material and Methods Between 2014 january and 2017 december we treated 48 patients with non-resectable Glioblastoma multiforme with hypofractioned radiotherapy. 53% were males. The average age was 54 years-old.The media total dose administrated was 70 Gy (66-74 Gy) The media dose per fracction was 2,45 Gy ( 2,2-2,6)38 patients were treated with IMRT (79%). Brain stem, optic pathways, pathway and motor cortex were protected, with a prescribed maximum dose of 54 Gy to brain stem and optic pathway and 60 Gy to motor pathway and cortex respectively. Results 6 patients didn´t finish radiotherapy treatment due to neurological clinical worsening caused by dissease progression, observed on CT scam (12%). In the remaining patients an incresed acute side effects were not observed during the radiotherapy treatment. On the one-month follow-up MRI an incresed of edema and contrast enhancement were observed in 31 patients (64%). These radiological findings improved in successive MRI in 25 patients (52%) Media overall survival observed were 14 months. 9 patients underwent surgery after radiotherapy treatment. Radionecrosis was observed in 6 anatomopathological studies. The media overall survival in these patients were 18 months (14-23 momths). Conclusion Hypofractioned radiotherapy is a well-tolerated treatment for unresetable Gliobastomas patients. The contrast enhacement on the 1-month follow-up MRI was due to Pseudoprogression, and associated to a good prognosis. Radionecrosis after surgical resection is associated to a better prognosis too. Hypofractionated radiotherapy treatment improves overall survival in these patients.

EP-1241 Radiosurgery reirradiation of brainstem: clinical evaluation and its radiobiological correlation. V. Pinzi 1 , D.M. Elena 2 , M. Marchetti 1 , L. Fariselli 1 1 Fondazione IRCCS Istituto Neurologico C. Besta, Neurosurgery- Unit of Radiotherapy, Milan, Italy ; 2 Fondazione IRCCS Istituto Neurologico C. Besta, Health Department, Milan, Italy Purpose or Objective The main studies focused on radiosurgery-induced toxicity to the brainstem are only few. One of the largest studies by Trifiletti et al. analyzed 547 patients with 596 brainstem metastases treated with SRS. The authors found that brainstem tumor location or volume of tissue receiving 12 Gy were not correlated to a severe toxicity. On the other hand, Foote et al . analyzed 149 patients and concluded that doses ≥15Gy to the brainstem conferred a significant increase in risk for cranial nerve complications and that the dosimetric factors predictive of cranial nerve palsy included Dmax ≥17.5 Gy and prescribed dose ≥12.5 Gy. However, there are even less studies about radiosurgery re/irradiation of brainstem, unless for the impact of previous WBRT on the toxicity rate after SRS for brainstem metastases. The objective of the study was to analyse the radiation-related toxicity of the brainstem radiosurgery re-irradiation and its correlation with radiobiological parameters. Material and Methods We analyzed 12 patients who underwent re-irradiation for progression or relapse of tumors of the brainstem or close to it. The toxicity was recorded based on CTCAE scales. The clinical results were correlated with radiobiological parameters through the linear-quadratic model to express the re-irradiation tolerance in cumulative equivalent total doses when applied in 2Gy fractions (EQD2cumulative). We used α/β values of 2.1 and 3.3Gy. Results The histology was high-grade glioma in 4 patients, metastases in 5, meningioma in 2 and unknown in 1 patient. Three patients underwent 5 radiation treatments (1 3Dconformal RT, 4 SRS), 1 patient received 4 RT treatments (1 3DCRT and 3 SRS), 1 patient received 3 RT treatments (3 SRS), 6 patients received one 3DCRT and 1 SRS course, 1 patient received two SRS treatments. The cumulative EQD2 (3,3) ranged 26.5–116.2Gy (mean ± S.D: 73±26.9Gy). The cumulative EQD2 (2,1) ranged 30.5– 130Gy (mean ± S.D: 79.5±29.4Gy). The mean time interval between radiotherapy courses was 18.7 ± 20 months (range 0-72 months; median 12 months; n = 23). The mean PTV was119.9±369.5cc (range 0.1– 1455.6). The mean follow-up was 44 months (range 10-145 months). At the time of analysis 7 patients were alive. No radionecrosis was reported. Only 1 patient developed G1 ataxia and dysphagia and only 1 patient developed a G2 ataxia. Both patients showed a neurological improvement after 1 month of corticosteroid therapy. Conclusion The overall outcome in the twelve described patients seems to be encouraging. Modern irradiation systems make it reasonable to administer successive irradiation treatments. Involving only 12 patients, this analysis cannot be expected to provide ground for us to draw definitive conclusions. However, the retrospective EQD2 values reported in this study can be used as starting point for a study focused on dose-reference for safe re- treatments. EP-1242 Multisession radiosurgery re-irradiation for glioblastoma recurrence: a retrospective analysis. V. Pinzi 1 , A. Viola 2 , M. Marchetti 1 , P. Gaviani 3 , E. Anghileri 3 , L. Fariselli 1 1 Fondazione IRCCS Istituto Neurologico C. Besta, Neurosurgery- Unit of Radiotherapy, Milan, Italy ; 2 University of Milan, Radiation Oncology, Milan, Italy ;