ESTRO 36 Abstract Book

S849 ESTRO 36 _______________________________________________________________________________________________

objectives were to cover at least 95% of the planning target volume with the 100% isodose. The generated plans were evaluated in terms of dose distribution of PTV(D95,D98,D max ), doses of total lungs (V20,V10,V5), heart(V30,V20 and mean dose).

(Varian Medical System) with 5mm leaf width (Millennium MLC). Plan were optimized using Auto-Planning (AP) (Philips Radiation Oncology Systems) and using one single AP template. Plan results were compared to published dose volume histogram (DVH) parameters for HS WBRT. Dose to 2% (D2%) and 98% (D98%) of the target volume and homogeneity index (HI) were evaluated. The hippocampus dose was evaluated based on the minimal dose (D100%) and the maximal dose (Dmax). In addition to DVH parameters evaluation, the effective planning time defined as the working time required between the volumes definition and the end of the plan optimization was evaluated. Results Target and hippocampus DVH parameters are shown in Table 1. The D2% to the brain was reduced on average by > 3Gy [MG1] (34 Gy vs. RTOG 37.5Gy) and the maximum hippocampus dose was reduced by > 1Gy. All the other parameters were similar to published data. The effective planning was kept below 10’ for each patient. Conclusion Automated TP for HS WBRT with VMAT achieved significantly decreased maximal brain dose and maximal hippocampus dose while fulfilling all other RTOG 0933 constraints. With this approach, hot spots > 115% could be significantly reduced in contrast to a maximal allowance of 130% in the RTOG protocol. EP-1576 Tomotherapy WBRT with SIB planning for patients with brain metastases D. Synchuk 1 , S. Odarchenko 1 , N. Seryogina 1 , O. Zinvaliuk 1 , M. Gumeniuk 1 , K. Gumeniuk 1 1 Ukrainian center of Tomotherapy, RT department, Kirovograd, Ukraine Purpose or Objective Whole brain radiation therapy (WBRT) is usually the primary treatment option for patients with multiple brain metastases extending median survival time and improving the quality of life. The aim of this study is to develop at our institution the technique for tomotherapy planning of WBRT with simultaneous integrated boost (SIB) for metastases. Material and Methods The target/OAR volume delineation was performed using MIM software. The PTV1 for SIB included GTV for metastases which was defined as the contrast-enhancing lesions on T1-weighted MRI plus 3 mm uniform margin. The PTV2 for WBRT included the whole brain plus 3 mm margin excluding PTV1. The aim of planning was to deliver the 40/30 Gy dose in 10 fractions to SIB/WBRT respectively. Prescription was made to the median dose, also D 99% should be ≥ 95% D presc and D 1% ≤ 107% D presc . Results The development of the standartised planning procedure began after treatment of 8 patients and gaining some experience. For planning purposes an automated workflow to produce additional contours was created: 2 consecutive 5 mm rings around the PTV1 to form the dose falloff; PRV structures as 3 mm outer ring contours for optic nerves, chiasm and brainstem; the structures that overlapped PTV were subdivided into “PTV OAR” and “PTV OAR PRV”, the subvolumes created for overlapping regions, and “OAR Plan” and “OAR PRV Plan” for non-overlapping; a special logical volume PTV2_nR was created by extracting

Results The mean dose values for target volume and critic organs were displayed in Table-2. The average treatment time and monitor unit were 6.85min, 5868MU respectively.

Conclusion Bilateral breast treatment is complex and difficult due to the field junction problem with the standard techniques. However, based on the results of this study, HT plans have shown high homogeneity and coverage indexes of target volumes while reducing the lung and heart doses. We expect the increase of low dose region due to helical irradiation. However, by using complete blocking, we provide that the values remained at the tolerance limits. EP-1575 Automated VMAT planning for whole brain irradiation with hippocampus sparing J. Krayenbuehl 1 , M. Di Martino 1 , M. Guckenberger 1 , N. Andratschke 1 1 University Hospital Zürich, Department of Radiation Oncology, Zurich, Switzerland Purpose or Objective Whole-brain radiation therapy (WBRT) has been the standard treatment for patient with multiple brain metastases for decades. However, with broader application of stereotactic radiotherapy the use of WBRT has decreased in the past years to avoid possible adverse neurocognitive effects. With the advent of neuroprotective strategies such as hippocampus sparing (HS) the interest in WBRT has been revived. The gold standard constraints for HS WBRT were published by the RTOG 0933 in 2011. In this project, we an automated treatment planning (aTP) approach aiming especially at reduced hot spots in the normal brain. Material and Methods Fourteen consecutive patients treated with HS WBRT were enrolled in this study. The planning target volume (PTV) was defined as the whole-brain excluding the hippocampal avoidance regions defined as the hippocampal expanded by 5mm in three-dimensions. 10 x 3 Gy was prescribed to 92% of the target volume. All patients were planned with VMAT technique using four arcs and two couch kicks (300° and 60°). The plans were optimized for a Trilogy linac