ESTRO 37 Abstract book

S1056

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 espe- cially when protecting the live is particularly relevant. difficulties. Conclusion

EP-1942 Impact of different FFF photon beam energy on VMAT prostate cancers treatment C. Saravanan 1 , P. Mohandass 1 , N.K. Bhalla 1 , A. Puri 1 1 FORTIS HOSPITAL, Radiation Oncology, Mohali - Punjab, India Purpose or Objective To evaluate impact of different flattening filter free (FFF) photon beam energy on volumetric arc therapy (VMAT) for prostate cancer. Material and Methods For this study, three prostate patients with no nodal involvement treated with 79.20Gy/44fractions were chosen from clinical data base. All the plans were generated using VMAT technique in Monaco™ V5.1 treatment planning system(TPS) for Elekta Versa HD™ linear accelerator with 0.5cm leaf width at isocenter. The VMAT plan was generated using 6MV-FFF photon along with partial and full arc. By keeping all other planning parameter constant, only by varying energy, plans were re-planned for 10MV-FFF and 6MV&10MV-FFF photon energy. For plan comparison, Conformity (CI), Homogeneity index (HI), dose coverage to planning target volume (PTV), Mean dose, max dose and dose volume received by organ at risk (OAR) for bladder, rectum, left femur, right femur and small bowel were analyzed. In addition, integral dose to normal tissue (liter-Gray), total monitor unit (MU) and delivery time (mins) were analyzed. Results The CI for PTV was 1.0876±0.0399, 1.0776±0.0530 and 1.1315±0.0081 for 6MV-FFF, 10MV-FFF and 6MV&10MV- FFF respectively. Similarly, HI was 0.0989±0.0270, 0.1015±0.0281 and 0.0944±0.0231. The mean dose and dose received by 95% volume to PTV was slightly increased for 6MV&10MV-FFF as compared to 6MV-FFF and 10MV-FFF. In addition, mean dose and dose volume received by bladder, rectum, left femur, and right femur showed lesser dose in 6MV&10MV-FFF as compared to 6MV-FFF and 10MV-FFF. Similarly, max dose to small bowel was less for 6MV&10MV-FFF as compared to 6MV- FFF and 10MV-FFF. However, no significant difference was observed in integral dose, MU and treatment delivery time. Conclusion The plan quality was slightly better in combination of 6MV&10MV-FFF as compared to 6MV-FFF and 10MV-FFF. But no significant difference was observed use of