ESTRO 36 Abstract Book

S852 ESTRO 36 _______________________________________________________________________________________________

anteroposterior-posteroanterior (AP-PA) technique with volumetric-modulated arc therapy (VMAT) for TLI. Material and Methods Treatment plan for conventional AP-PA technique was performed with XiO treatment planning system (CMS, v. 5.00.01) and VMAT plan was performed with Elekta Monaco treatment planning system (v. 5.00.00), optimized using biological and physical based cost functions, on an Elekta Synergy linear accelerator equipped with a 160-leaf Agility MLC. Prescription dose was 8 Gy in 2Gy daily fractions. Patient was in supine position over a custom shaped vacuum bag device, along with an aquaplast mask for head position reproducibility. The arms were extended laterally. VMAT treatment consisted in 2 isocenters, with 4 cm overlap length and 2 partial arcs (290° - 70° and 135 - 210°) each. Linac treatment couch was included in the calculation. For both techniques, PTV coverage, conformation index (CI), conformation number (CN) and Heterogeneity index (HI) have been compared, as well as doses to organs at risk (OAR) and integral body dose. Results Table 1 shows the results obtained for the PTV and OARs. PTV coverage with both techniques was adequate (V95%= 91.5% and 95.3% for 3DRT and VMAT respectively), HI were similar, but conformation indices were better with VMAT technique. VMAT also improved the doses to the lungs, the heart and the spinal cord. Heart volume receiving 5 Gy or more (V 5Gy ) and receiving 8 Gy or more (V 8Gy ) was considerably lower in VMAT plan. Integral dose, calculated by the product of mean dose to the patient without the PTV and the irradiated volume was 11% lower in the VMAT plan and the mean skin dose 33% lower .

Conclusion Since the start of IORT service in Aug 2013, we have delivered 146 treatment fields to 130 patients with limited toxicity and excellent local control. In a busy service, IORT is not always a straightforward electron treatment, and staff experience and adequate data is important.’ EP-1580 Dosimetric comparison between 3D- conformal radiation therapy and VMAT in Total Lymphoid Irradiation C. Ferrer 1 , C. Huertas 1 , A. Escribano 1 , R. Plaza 1 , R. Morera 2 , A. Serrada 2 1 Hospital universitaria La Paz, Radiofísica y Radioprotección, Madrid, Spain 2 Hospital universitaria La Paz, Oncología Radioterápica, Madrid, Spain Purpose or Objective Total Lymphoid Irradiation (TLI) is used in the management of pediatric allogeneic hematopoietic stem cell transplantation (HSCT). This study compares the conventional 3D-conformal radiation therapy (3DCRT)

Conclusion Although both techniques achieve similar PTV coverage, VMAT plan shows higher level of conformation, with considerably lower mean skin dose and integral dose in spite of the low-dose spread. Doses to OAR are also lower with VMAT, specially the heart. VMAT technique can be very beneficial for pediatric patients undergoing TLI, with lower late organ toxicity. EP-1581 Dosimetric comparison of treatment plans for pancreatic cancer: 3DCRT, IMRT and VMAT P. Trecca 1 , M. Fiore 1 , B. Floreno 1 , R. D'Angelillo 1 , L. Trodella 1 , A. Mameli 1 , E. Infusino 1 , C. Greco 1 , L. Trodella 1 , S. Ramella 1 1 Campus Biomedico University, Department of Radiation Oncology, Roma, Italy