ESTRO 2021 Abstract Book

S875

ESTRO 2021

Pérez De Larraya 5 , L.H. González Quarante 6 , P. Dominguez Echávarri 7 , J.I. Echeveste 8 , M. Cambeiro Vázquez 3 , R.R. Maria 9 , J. Aristu Mendioroz 3 , V.M. Suarez Vega 10

1 clinica Universidad De Navarra, Radiation Oncology. Proton Therapy Center., Madrid, Spain; 2 clinica Universidad De Navarra, Radiation Oncology.Proton Therapy Center., Madrid, Spain; 3 clinica Universidad De Navarra, Radiation Oncology.Proton Therapy Center., Madrid , Spain; 4 clinica Universidad De Navarra, Nuclear Medicine, Pamplona, Spain; 5 clinica Universidad De Navarra, Neurology , Pamplona, Spain; 6 clinica Universidad De Navarra, Neurosurgery, Pamplona, Spain; 7 clinica Universidad De Navarra, Neuroradiology , Pamplona, Spain; 8 clinica Universidad De Navarra, Pathology, Pamplona, Spain; 9 clinica Universidad De Navarra , Radiation Oncology, Pamplona, Spain; 10 clinica Universidad De Navarra , Neuroradiology, Madrid, Spain Purpose or Objective Proton beam therapy (PBT) is an attractive high-precision radiation technology that minimizes low and intermediate radiation doses to the brain tissue of selected patients for protontherapy. [11C]Methionine Positron Emission Tomography (METPET) may contribute to a more precisely delimitation of the target volume and therefore the association of PBT and METPET can lead to decrease the ratio of acute neurological adverse effects in patients treated with conventional radiation therapy Materials and Methods Between April 2020 and January 2021 a total of 10 patients diagnosed of primary CNS tumors, with a median age of 50 years (range 24-67) were treated with 360º gantry, synchrotron-based PBT (Hitachi), at the Clínica Universidad de Navarra in Madrid. CT, MR and METPET images were utilized to radiation planning. The GTV was generated using the METPET areas with tumor to normal brain ratio >1.8 and the CTV were designed from the GTV with a 5-15mm of margin. Results The median follow up was 3 months (1m-7m). Out of the 10 patients treated, 4 (40 %) were glioblastoma, 4 (40%) anaplastic astrocytoma, 1 (10 %) anaplastic meningioma and 1 (10%) oligodendroglioma. In patients diagnosed of malignant glioma 3/8 had IDH1 mutated and 2/8 BRAF V600 mutation. Five patients were previously irradiated with a median initial radiation dose of 60 Gy (60Gy-66Gy). Median CTV volume was 50 cm 3 (4.5-84.1), median of prescribed dose was 57 Gy RBE (40Gy RBE-64Gy RBE) and the median of dose per fraction was 2,56 Gy RBE (2,5 Gy RBE-4 Gy RBE). Patients with anaplastic astrocytoma received 64Gy/25 fractions and selected patients with recurrent glioblastoma were treated with reirradiation 40Gy/10 fractions. Median PBT incidence fields were 2 (range 2-3). Immediate tolerance has been excellent and no acute toxicity grade 2 or higher was recorded. Metabolic imaging changes compatible with radionecrosis were present in 1 out of 4 re-irradiation patients. Significant CTV changes (mean 48% CTV decrease and 37% CTV increase) were introduced in this particular cohort adapted in PET-guided information compared to Flair/T1 Gad observed changes. Conclusion The combination PBT/METPET in CNS tumors modifies GTV definition and PBT protects healthy brain tissue from unnecessary irradiation. Our preliminary results using hypofractionation in terms of acute tolerance are encouraging. PO-1051 Proton versus photon craniospinal irradiation in Pediatric patients with high-risk medulloblastoma A. Lassaletta 1 , E. Panizo 2 , F. Vazquez 3 , F.J. Serrano 4 , E. Carceller 3 , C. Gonzalez-San Segundo 5 , J. Aristu 4 , F. Calvo 4 1 Clínica Universidad de Navarra, Radiation Oncology, Madrid, Spain; 2 Clinica Universidad de Navarra, Pediatric Oncology, Madrid, Spain; 3 Hospital Universitario Niño Jesús, Pediatric Oncology, Madrid, Spain; 4 Clinica Universidad de Navarra, Radiation Oncology, Madrid, Spain; 5 Hospital Universitario Gregorio Marañon, Radiation Oncology, Madrid, Spain Purpose or Objective Bi-Institutional retrospective study to examine the acute toxicity of craniospinal irradiation (CSI) in Pediatric patients with high-risk medulloblastoma using proton or photon therapy. Materials and Methods Clinical and treatment characteristics were recorded for 8 pediatric patients with high-risk medulloblastoma (residual tumor >1.5 cm 2 and or metastatic disease) who all received CSI with concurrent chemotherapy (weekly vincristine + daily carboplatin) in two institutions (4 patients received protons and 4 photons). Platelets were transfused if < 30,000. GCSF was administered if less than 1,000 absolute neutrophil count. Results Median age of children receiving proton and photon CSI was 10.5 years for both groups. High-risk features included M3 in 5 patients, residual >1.5 cm 2 in 2, and M1 in one patient. Three patients in each group had a VP shunt. All patients received between 36 to 39.6Gy CSI and a boost to posterior fossa for a total dose of 55.8 Gy. All patients received exactly the same treatment protocol. Median days duration or radiotherapy were 46.5 days (range, 42 – 52) for proton and 48.5 days (range, 43-58) for photon. None of the patients in the proton group had any grade 3/4 non-hematological acute toxicity, while in the photon group, one patient experienced grade 3 nausea, vomiting, esophagitis, constipation, and anorexia, and another patient experienced grade 3 abdominal pain. Five and 6 red blood cell transfusions were received by proton and photon patients respectively. Proton patients did not need any platelet transfusions while photon patients received 2. A median of 9.5 doses (range, 5-14) and 16.5 doses (range, 3-20) of G-CSF were administered in the proton and photon groups. Three of the 4 patients in the photon group had to be admitted during radiotherapy while no patient in the proton group was admitted. Conclusion Pediatric patients with high-risk medulloblastoma who received proton CSI seemed to experience less acute