ESTRO 36 Abstract Book

S850 ESTRO 36 _______________________________________________________________________________________________

previously made rings from PTV2 for more clear DVH and statistical analysis. Being completely involved into the target volume such OARs as optic chiasm and brain stem including their PRVs were added to “Target Constraints” tab along with other PTVs for better dose control in this areas. For the most conformal treatment plan deliverable in a reasonable time, all plans were generated using a 2.5 cm field width, pitch 0.295 and the final modulation factor of 2.1. The template was made within the treatment planning system (TPS). All previously treated patients were replaned and target coverage was analyzed for PTV1 and PTV2_nR in terms of homogeneity index (HI) and conformation number (CN),

metastases were selected. Radiotherapy was prescribed according to simultaneous integrated boost technique with all targets irradiated simultaneously over 10 daily fractions. Doses of 30 Gy and 50Gy were prescribed to PTV whole-brain and PTV mets , respectively. Bilateral hippocampi were delineated according to RTOG 0933 trial suggestions, on T1w MRI co-registered planning CT. Clinical standard plans (s-IMRT) were compared with plans aiming to spare hippocampus irradiation. Two plans were re-optimized for hippocampal sparing using two Elekta MLCs: MLCi2 with 10mm leaf width (hs10-IMRT) and Agility with 5 mm leaf widths (hs5-IMRT). All plans were evaluated using target coverage metrics, homogeneity index (HI) and conformity index (CI). Normal tissue complication probabilities (NTCP) for neurocognitive function impairment (NCF) were calculated using a predictive model developed by Gondi et al. Results Plans aiming to hippocampus sparing demonstrated comparable planning target volumes coverage and no differences in sparing of other organs at risk (brainstem, optic chiasm, eyes, lens). Significant reductions in hippocampal doses relative to standard plans were achieved in all patients. Mean dose to bilateral hippocampi was reduced from 36.5 Gy (range: 34.7-37.7 Gy) to 17.4 Gy (range: 11.2-24.7 Gy) and 16.4 Gy (range: 11.0-24.1) for hs10-IMRT and hs5-IMRT plans, respectively. D40% was reduced from 36.9 Gy (range: 35.3-37.7 Gy) to 18.2 Gy (range: 11.8-25.2 Gy) and 17.2 Gy (range: 11.5- 25.0 Gy) for hs10-IMRT and hs5-IMRT plans, respectively. Mean NTCP values for NCF impairment as predicted by Gondi model decreased from 98.0% (range: 97.7-98.5%) to 62.1% (range: 34.8-83.9%) and to 58.2% (range: 33.4- 83.5%) for hs10-IMRT and hs5-IMRT plans, respectively. Dose reductions depended mainly on metastases location and distance from hippocampus. Conclusion IMRT plans aiming at sparing bilateral hippocampi can be successfully optimized with SIB-IMRT despite the high- dose irradiation of multiple brain metastases, providing a significant reduction in NTCP for radiation induced NCF decline. EP-1578 Frameless intracranial radiosurgery with Helical Tomotherapy: preliminary results. M. Iacco 1 , C. Zucchetti 1 , M. Lupattelli 2 , C. Aristei 2 , C. Fulcheri 1 , R. Tarducci 1 1 Santa Maria della Misericordia Hospital, Medical Physics Department, Perugia, Italy 2 Santa Maria della Misericordia Hospital, Radiation Oncology Department, Perugia, Italy Purpose or Objective To report the preliminary results of radiosurgery treatments with Helical Tomotherapy (HT) by means of an non-invasive frame. Material and Methods Between April and October 2016, 6 patients underwent radiosurgery with HT for treatment of 10 brain lesions with a median dose prescription of 20 Gy (range 15-22 Gy). The planning target volume (PTV) was created expanding 2mm in all directions the gross tumor volume (GTV). The median PTV was 1.5cc (range 0.6-7.7cc). Treatment plans were performed with the following parameters: field width of 1.05cm, pitch in the range 0.108-0.150, and modulation factor (MF) in the range 1.5-3.5, leading to a final MF of 1.6 on average (range 1.1-2.2). All plans were prescribed according to ICRU83 at the median of PTV, trying to limiting cold (D 98% >95%) and hot spots (D 2% <107%). In addition, 12Gy-volumes (V 12Gy ) of the healthy brain, associated with symptomatic radiation risk of necrosis, was reduced below 10cc. Treatment plans were analyzed recording D 98% , D mean and D 2% of the PTV. Moreover the

where TV 95%

- tumor volume covered with 95% isodose, TV

– tumor volume, V 95% - volume of 95% isodose. The results are shown in the table below.

Conclusion The development and implementation of standard technique for WBRT with SIB allowed us to much faster treatment planning performance using automated workflows for additional structures creation and TPS template for lower machine time used. The treatment time was decreased from 8.09±2.98 min to 6.85±0.95 min (p=0.05). New plans showed good homogeneity (HI 0.071±0.047 for PTV1 and 0.072±0.015 for PTV2_nR) and conformity (CN 0.794±0.169 for PTV1 and 0.82±0.077 for PTV2_nR) (p=0.05) with good OAR sparing. EP-1577 Hippocampus-sparing whole-brain IMRT and simultaneous integrated boost to multiple brain metastases S. Cilla 1 , F. Deodato 2 , M. Ferro 2 , G. Macchia 2 , A. Ianiro 1 , V. Picardi 2 , M. Boccardi 2 , M. Ferro 2 , S. Cammelli 3 , A. Arcelli 3 , E. Farina 3 , L. Giaccherini 3 , G.P. Frezza 4 , V. Valentini 5 , A.G. Morganti 3 1 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy 2 Fondazione di Ricerca e Cura "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, Radiation Oncology Unit, Campobasso, Italy 3 Università di Bologna, Radiation Oncology Center- Department of Experimental- Diagnostic and Specialty Medicine - DIMES, Bologna, Italy 4 Ospedale Bellaria, Radiation Oncology Department, Bologna, Italy 5 Policlinico Universitario "A. Gemelli"- Università Cattolica del Sacro Cuore, Radiation Oncology Department, Roma, Italy Purpose or Objective High dose irradiation to hippocampus is critical in determining neurocognitive function (NCF) outcomes. We evaluated the feasibility of intensity-modulated whole- brain radiotherapy (IMRT) and simultaneous integrated boost (SIB) to multiple brain metastases (BMs) to generate hippocampus-sparing plans. Material and Methods 5 patients with a total of 16 BMs who previously underwent whole brain radiotherapy with boost to multiple