ESTRO 37 Abstract book

S885

ESTRO 37

Results A considerable variation in target segmentation was seen in both cases. For case 1 the variation was 374-960 cm 3 (average 669 cm 3 ) and for case 2; 65-126 cm 3 (average 109 cm 3 ).

selected metastatic site. Disease stage was classified according to the International Neuroblastoma Staging System (INSS). We evaluated the recurrence pattern (local, systemic), progression free survival and overall survival. Results A Total of 33 patients with high risk neuroblastoma were included in this study. The median age of patients was 4 years (range, 1-11 years). Twenty four patients (73%) were INSS stage 4 and eight patients were INSS stage 3. At the median follow up of 63 months, there were 6 cases of local recurrence and 10 cases of systemic recurrence. Among six local failure cases, four relapsed adjacent to the radiation field. Other two relapsed in the radiation field (para-aortic, retroperitoneal). Among these, one underwent R2 resection and tumor recurred at residual lesion. The main sites of distant metastasis were bone marrow, bone, lymph nodes. Median overall survival was 63 months and median progression free survival was 58 months. Conclusion Radiation therapy directed at the primary tumor site shows good local control. It appears to be adequate for local control for patients with high-risk neuroblastoma after chemotherapy and surgical resection. Because only 33 patients were analyzed in this study, additional study is needed. EP-1642 Evaluation of inter-observer variations in target delineation – A dose based approach Kristensen 1 , K. Nilsson 2 , T. Knöös 1 , P. Nilsson 1 1 Skane University Hosplital Lund- Lund University, Radiation Physics, Lund, Sweden 2 Clinical Oncology- Uppsala University Hospital, Department of Immunology- Genetics and Pathology- Experimental and Clinical Oncology- Clinical Oncology, Uppsala, Sweden Substantial inter-observer variations in target delineation have been presented previously. Target delineation for paediatric cases is particular difficult due to the small number of patients, the variation in paediatric targets, the number of study protocols, and the individual patient’s specific needs and demands. Uncertainties in target delineation might lead to under- or over-dosage. The aim of this work is to apply the concept of a consensus volume combined with good quality treatment plans to visualise and quantify inter-observer target delineation variations in dosimetric terms in addition to conventional geometrically based volume concordance indices. Material/methods Two paediatric cases were used to demonstrate the potential of adding dose metrics when evaluating target delineation diversity; a Hodgkin’s disease (case 1) and a rhabdo–myosarcoma of the parotid gland (case 2). The variability in target delineation (PTV delineations) between six centres was first quantified using the generalised conformity index, CI gen , generated for volume overlap. Secondly, the STAPLE algorithm, as implemented in CERR, was used for both cases to derive a consensus volume. STAPLE is a probabilistic estimate of the true volume generated from all observers. Finally, dose distributions created by each centre for the original target volumes were then applied to this consensus volume. Purpose or Objective Background/urpose

Figure 1. Case 1 (left) and case 2 (right) with all centres’ delineations and the consensus volume in yellow. CI gen were 0.53 and 0.70, respectively. Each dose distribution were applied to both its own target as well as to the consensus volume. The DVHs in absolute volume displayed for the delineated target volume as well as for the consensus volume adds information on both “compliant” target volumes as well as outliers which are hidden with just the use of concordance indices.

Figure 2. Examples of individual DVHs for target volumes (dashed lines, centres 3 to 4) for case 1 compared to the consensus volume (solid yellow line). To the left a substantial under-dosage of the consensus volume is present, and to the right an over-dosage of the consensus volume is present. Conclusion DVHs in absolute volume adds information that is more understandable and interpretable compared to various indices for evaluating uniformity in target delineation. The DVHs displayed for the consensus volume adds information on both “compliant” target volumes as well as outliers which are hidden with only the use of concordance indices. This approach should be reported together with descriptive statistics, concordance indices and statistical measures of agreement to get a complete evaluation of delineation studies. S. Di Biase 1 , M. Trignani 1 , C. Di Carlo 1 , I.P. Voicu 2 , L. Gentile 2 , A. Augurio 1 , M. Caulo 2 , A. Vinciguerra 1 , D. Genovesi 1 1 "SS. Annunziata" Hospital- "G. D'annunzio" University, Radiotherapy, Chieti, Italy 2 "SS. Annunziata" Hospital- "G. D'annunzio" University, Radiology, Chieti, Italy Purpose or Objective Brain maturation and myelination is a dynamic process starting in fetal life and evolving during the first years of life. Magnetic resonance based atlases for hippocampus contouring in radiotherapy of brain tumors in adults are available, while similar tools are not currently available for pediatric population. The aim of our study was to verify if reference atlases for hippocampal contouring could be used in paediatric brains and to evaluate the feasibility of hippocampal delineation in childhood. EP-1643 Applicability of reference atlases to hippocampal contouring in paediatric radiotherapy