Abstract Book

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ESTRO 37

hippocampal volumes were smaller for manual vs auto- segmentation (left 1.99cm 3 vs 2.26cm 3 ; right 2.15cm 3 vs 2.42cm 3 ). The mean PTV D98%, D95%, D90% and D2% were higher for IMRT vs VMAT plans (24.6Gy vs. 23.9Gy, 27Gy vs. 26.2Gy, 28.4Gy vs. 27.8Gy and 31.5Gy vs. 31.3Gy). There was no clinically significant difference between IMRT and VMAT in doses delivered to OARs. The hippocampal mean dose and D2% was only slightly higher for IMRT vs VMAT (left 10.2Gy vs. 9.5Gy and 12.6Gy vs. 12.2Gy; right 10Gy vs. 9.1Gy and 12.6Gy vs. 12.1Gy). The average monitor units (MU) for IMRT was higher compared to VMAT (2204 vs. 644), while the optimization time was higher for VMAT (628 vs. 1220 seconds). Conclusion Auto-segmentation is a useful tool to generate hippocampal volumes and potentially reduce contouring time, however manual editing is still required. Both IMRT and VMAT produced clinically acceptable plans, although VMAT had lower MUs, which would result in lower normal tissue scatter dose, and reduced treatment delivery time, critical in resource limited environments. The results of this study will be used in implementing HAWBRT for BC patients with BM in a prospective study setting. EP-1941 Liver sparing by using the deep inspiration breath hold technique for right breast radiotherapy C. Tamburella 1 , G. Faessler 1 , G. Guibert 1 , L. Hirschi 1 , L. Pion 1 , P. Weber 1 , P. Tsoutsou 1 1 Hôpital Neuchatelois, radiotherapie, la chaux de fonds, Switzerland Purpose or Objective The deep inspiration breath hold technique (DIBH) is widely used for left breast radiotherapy (RT) to reduce the dose to the heart by moving it away from the irradiated breast. Applying this technique for RT of the right breast might reduce the irradiated liver tissue. Combining DIBH with volumetric arc therapy (VMAT) provides a precise delivered dose to the breast. In this study, we show the advantages of using VMAT-DIBH compared to free breathing (FB) VMAT for RT of the right breast. Material and Methods Seventeen patients with cancer of the right breast, eligible for a VMAT-DIBH treatment, had two CT scans : one in FB and one in DIBH. Thirteen of them had a local (L) RT and 4 of them a locoregional (LR) one. Organ delineation was performed on both scans, and two treatment plans (FB and DIBH) were optimized with the planning system Pinnacle 14 (Philips). For the same planning target volume (PTV) coverage, both plans were compared by looking at the dose at the organs at risk (OAR) : liver, lungs, heart, and contralateral breast. Results For the same PTV coverage, there is a liver dose reduction in DIBH due to the liver displacement out of the irradiation field. Applying the DIBH technique, the V10Gy becomes negligible (<0.1%) and the V5Gy was 1.1±1.0% and 0.3±0.5% for L and LR RT respectively, when the mean dose was also very low 0.9 ±0.4Gy for L-RT and 0.6±0.4Gy for LR-RT. The doses at the heart, lungs, and the contralateral breast were equivalent in DIBH or FB for L-RT (Figure 1). For LR-RT, DIBH induced a slight decrease of the mean dose at the heart and contralateral breast, and an important dose reduction for the ipsilateral lung (20%) (Figure 2). All patients received successfully their treatment in DIBH, with no major A good PTV coverage and a very low dose at the liver, while preserving the other OARs was achieved with DIBH. This technique should be applied more frequently for right-sided breast RT on an individual-patient basis especially when protecting the live is particularly difficulties. Conclusion

Conclusion If the tumor volume is more than 0.5 cm3, Cyberknife with InCise multi-leaf collimator can achieve plan quality with sharper peripheral dose fall-off as well as better conformity than Cyberknife with fixed collimator for brain stereotactic radiosurgery. EP-1940 Hippocampal avoidance whole brain radiotherapy: a comparison of contouring and planning techniques G. Kothari 1 , P. Rich 2 , K. Amin 3 , G. Ross 4 1 Royal Marsden Hospital Trust & Institute of Cancer Research, Breast unit, London, United Kingdom 2 The Royal Marsden NHS Foundation Trust, Department of Diagnostic Radiology, London, United Kingdom 3 The Royal Marsden NHS Foundation Trust, Joint Department of Physics, London, United Kingdom 4 The Royal Marsden NHS Foundation Trust, Breast unit, London, United Kingdom Purpose or Objective Hippocampal avoidance whole brain radiotherapy (HAWBRT) has been shown to reduce the adverse neurocognitive effects of WBRT. This is relevant in patients with breast cancer (BC) for whom improvement in systemic therapy has seen a rise in the incidence of brain metastases (BM), as well as survival, such that late neurocognitive effects of WBRT are becoming increasingly relevant. This planning study compares manual with auto- segmentation contouring of the hippocampus, and intensity modulated radiotherapy (IMRT) with volumetric modulated arc therapy (VMAT) in the delivery of HAWBRT in patients with BC and BM. Material and Methods 10 patients with BC and BM who had available diagnostic MRI and planning CT images from prior RT were chosen. Manual contouring of hippocampal volumes was performed by a radiation oncologist and neuroradiologist, with reference to the Radiation Therapy Oncology Group (RTOG) hippocampal contouring atlas. Auto-segmentation of the hippocampus was performed using Brainlab Elements (Brainlab, Feldkirchen, Germany) auto- segmentation software. Manual and auto-segmentation of hippocampal contours were compared using the Dice Similarity Coefficient (DSC). A DSC value of > 0.8 was pre- determined to be a clinically acceptable value from available literature. IMRT and VMAT plans were generated using Eclipse treatment planning system TM (Varian Medical Systems Inc.). Plans were prescribed to a median of 30Gy in 10 fractions, using the HIPPO trial protocol (ClinicalTrials.gov ID: NCT02147028) to guide planning target volume (PTV) coverage and organ at risk (OAR) constraints. OARs included the lens, eyes, optic nerves, optic chiasm, parotids, and cochlea. Results The average DSC for manual compared to auto- segmentation contouring of the left and right hippocampus was 0.66 and 0.67 respectively. The mean