ESTRO 38 Abstract book

S460 ESTRO 38

groups no hematological toxicity differences were observed (4 G3 leuko-neutropenia,3DCRT:2/5,VMAT:2/6). G3 toxicity occurred in all HR pts.G4 (leuko-neutropenia, thrombocytopenia) was recorded in 4 VMAT pts, 3 of whom received ASCT before HART. More use of G-CSF and transfusions during and after RT was required for VMAT pts, and 1 ASCT-VMAT child stopped earlier HART due to hematological toxicity. Pts irradiated with VMAT and undergoing ASCT showed a more pronounced and persistent leukopenia during and after HART (Figure). Evaluation of mean absorbed doses by iliac bones showed a significant difference in pts treated with 3DCRT (0.9 Gy) or VMAT (5.8 Gy).

Conclusion No statistically significant differences in OS, DFS and LC were observed between the complete resection group and the boost group, considering that it is a small series with limited follow-up of some patients. These results are consistent with other published data considering the potential benefit in LC and OS of a radiation boost to residual tumour in incompletely resected ependymoma patients, although further investigation is necessary. PO-0872 Hematological toxicity of 3DCRT and VMAT craniospinal irradiatiation in pediatric medulloblastoma B. Diletto 1 , E. Pecori 1 , O. Alessandro 2 , S. Meroni 3 , T. Giandini 3 , C. Stucchi 3 , C. Cavatorta 3 , E. Schiavello 4 , V. Biassoni 4 , M. Massimino 4 , E. Pignoli 3 , L. Gandola 1 1 Fondazione IRCCS Istituto Nazionale dei Tumori, Radiation Oncology 1, Milan, Italy ; 2 Università degli Studi di Milano, Residency Program in Radiation Oncology, Milan, Italy ; 3 Fondazione IRCCS Istituto Nazionale dei Tumori, Medical Physics, Milan, Italy ; 4 Fondazione IRCCS Istituto Nazionale dei Tumori, Pediatric Oncology, Milan, Italy Purpose or Objective Craniospinal irradiation (CSI) is a milestone of the postoperative treatment of pediatric standard risk (SR) and high risk (HR) medulloblastoma (MB).Advantages of VMAT technique for CSI in term of target coverage and organ sparing have been documented, but it causes exposition of red bone marrow to low doses, worsening hematopoiesis. Aim of the study was the evaluation of hematological toxicity of pediatric SR and HR MB pts treated with 3DCRT or VMAT-CSI. Material and Methods RT and clinical details of SR and HR MB pts treated in our Institution were collected. Prescription doses to SR patients: 23.4 Gy/1.8 Gy daily to craniospinal axis, followed by a tumor bed boost up to a total dose of 54 Gy. All SR children then received a standard maintenance chemotherapy (CT). Prescription doses to HR patients: hyperfractionated accelerated RT (HART) with CSI doses of 39 Gy or 31.2 Gy/1.3 Gy bid, depending on age, followed by a boost to the tumor bed up to a total dose of 59.8 Gy when indicated. Before HART all HR pts received high-dose sequential CT. HR pts with persistent disease before HART, were consolidated with 2 courses of myeloablative CT and autologous stem cell transplant (ASCT) before irradiation, while the remaining received standard maintenance CT after HART. Hematological changes were recorded weekly during RT and scored according to RTOG system. Mean RT doses to iliac bones were collected to evaluate dose to red bone marrow. Results Data from 26 patients (SR: 11,HR: 15) were collected (median age 10 y,4-33): 10 pts received 3DCRT (SR: 5,HR: 5), 16 pts VMAT (SR:6,HR:10). 4 HR pts were consolidated with 2 ASCT before HART (3DCRT:1,VMAT:3). Within SR

Conclusion Low doses irradiation of red bone marrow during VMAT-CSI has the potential to interfere with hematopoiesis implying a more severe hematological toxicities in HR pts who received ASCT before HART. Hence, to reduce toxicity during VMAT-CSI, at least in this subgroup, iliac bones should be contoured as OAR and a planning effort is strongly recommended to lower mean dose to these structures. Nevertheless, hematological toxicity in our series was never life threatening and always reversible and we continue to recommend VMAT for CSI due to the documented advantages of this technique in sparing higher RT doses to other vital organs such as heart, lungs and liver. PO-0873 Associations between vessel volume and neurocognition In children treated with proton therapy A. Srivastava 1 , J. Contreras 1 , H. Heimos 1 , S. Perkins 1 1 Washington University School of Medicine, RADIATION ONCOLOGY, Saint Louis, USA Purpose or Objective Vasculopathy is a well-recognized late side effect of radiotherapy (RT) in the pediatric population, and RT- induced cerebrovascular injury is thought to induce neurocognitive impairment. In this study we sought to further characterize this relationship by evaluating the effects of proton beam RT (PBT) on volumetric changes in the cerebral vasculature and corresponding changes in neurocognitive function. Material and Methods In this prospective study, we evaluated 13 children, ages 4-21, with a primary CNS malignancy treated with PBT. Magnetic resonance imaging of the brain (bMRI) was obtained pre-treatment and at scheduled follow-up visits post-RT every 3-6 months, and substructures were auto- segmented on MPRage sequences using a well-validated auto-segmentation program. Patients completed neurocognitive testing using the National Institutes of Health Toolbox Cognitive Battery (NIH-TCB) at baseline and during follow-up visits within three months of their bMRIs. Using linear mixed effects models, we evaluated the effects of age, time since PBT, and RT dose on cerebral vessel volumes and TCB metrics. Results The median age at RT was 14 years (range 4-19), and median follow-up time was two years (range 0.5-2.9). The plurality of patients was treated for medulloblastoma