Abstract Book

S886

ESTRO 37

Material and Methods VMAT and PBS-PT dose distributions were calculated for 10 WT patients (average 2, range 1-4 years), with prescription doses (PD) ranging between 10.8-14.4 Gy, and 10 NBL patients (average 4, range 1-7 years), with PD of 21.6 Gy. The treatment plans were robustly optimized on the clinical target volume (CTV). A uniform 5 mm patient set-up uncertainty was used for both delivery techniques. Moreover, for the PBS-PT plans a 3% proton range uncertainty was accounted for. VMAT plans were based on a 6MV full-arc while PBS-PT plans on 2-3 posterior fields to avoid uncertainties due to bowel filling and organ motion. To reduce the risk of asymmetric skeletal growth, a homogeneous dose was aimed for the vertebral bodies (VB) adjacent to the CTV (accepted gradient <5 Gy within one VB). As there is no international consensus in how to treat the VB, both PBS- PT and VMAT plans were created with and without accounting for the constraint to the VB (V 95-97% > D 80% ). The plan robustness was evaluated using multiple dose distributions associated with various error scenarios: set- up errors (with the magnitude of 5 mm in 26 directions per VMAT and PBS-PT plans) and range errors (±3% density scaling, resulting in 52 scenarios per PBS-PT plan). Plans were accepted if the V 95% of the CTV > 98% in the voxel-wise minimum evaluation dose. Mean dose (D mean ) and dose-volume statistics were computed to assess CTV coverage and organs at risk (OAR) and body sparing (p<0.05, Wilcoxon). Results For both techniques, the CTV coverage was fulfilled. Significant better sparing of the OARs and body was achieved with PBS-PT for both WT and NBL patients (Table 1). The maximum reduction of the D mean to the OAR was up to 37% for WT patients and 34% for NBL patients. The volume of the body receiving high dose levels (V >95% ) was reduced up to 3% and 1% while the volume of the body receiving low dose levels (V <2Gy ) was reduced up to 31% and 39%, for WT and NBL patients respectively. Moreover, significant differences were found between plans optimized accounting and not accounting for the VB for each delivery technique (Table 2). A reduction of the D mean to the OAR up to 8% and 5% and to the body up to 3% and 1% was denoted for VMAT and PBS-PT plans, respectively.

Conclusion When compared to VMAT, PBS-PT presents equal target coverage. In addition, a reduction of the dose to the OARs and body is achieved with PBS-PT. Thus, chances of reducing radiotherapy side effects might increase with PBS-PT over VMAT. Moreover, sparing of the OAR and body can be achieved while not accounting for the constraint to the VB in the planning. Thus, clinical guidelines concerning the VB should be established for these tumor sites. J.S. Ali 1 , L.Y. Mula-Hussain 1 , S. Othman 2 , K. Marif 2 , N. Othman 2 , S. Ali 2 , B.M. Muhsin 2 , S. Majid 2 , A.H. Gendari 2 , A. Kamal 2 1 Zhianawa Cancer Centre, Radiation Oncology, As sulaimanyah, Iraq 2 Zhianawa cancer Center, Radiation Oncology, Sulaymaniyah, Iraq Purpose or Objective The aim of the study is to evaluate the mode of the clinical presentations, staging distribution and the survival outcomes of WT patients in our institution. Material and Methods Retrospective study on 50 WT patients who had been managed at our oncology complex in Northern Iraq in ten years (from January 2007 to January 2017). Comparison with other relevant published literature was accomplished. Statistical Package for Social Science (SPSS) software (version 20.0) is used while the survival outcomes were analyzed by Kaplan-Meier method. Results 50 children (29 females and 21 males) were analysed. Median age at time of diagnosis was 2.7 years (ranged 0.7-10.1). The distributions of stages were as follows; stage I 40%, stage II 2%, stage III 44%, stage IV 6% and stage V 8%. Favorable histology was diagnosed in 96% and unfavorable histology in 4% of the patients. The National Wilms' Tumor Study strategy were used in the treatment of these cases. Neoadjuvant chemotherapy was given in 34% and all of them received adjuvant chemotherapy. 62% of patients received radiation postoperatively. The 4- year overall survival and Event-free survival were 80% and 60%, respectively. EP-1646 Wilms' Tumor in a war-torn nation: 10-year single institution experience from Iraq