ESTRO 36 Abstract Book

S447 ESTRO 36 2017 _______________________________________________________________________________________________

anterior descending artery (LAD), and the thyroid, were compared to those of non-coplanar 3D-CRT and coplanar VMAT. A p value < 0.05, derived using the paired Student’s t-test, was considered to reflect a significant difference. Results Figure 1-B shows the averaged dose-volume histograms for all 24 patients in terms of their PTVs and OARs. The Table summarizes the mean dose volume indices for the targets and OARs, and the MU for each technique. Significant difference was not observed in doses to the PTV. When DWA was employed, the average V 20Gy , V 10Gy , and V 5Gy to the ipsilateral lung; the average V 10Gy and V 5Gy to the heart; the D 2% for the planning organ at risk volume of the LAD (PRV_LAD); and the V 50% of, and the mean dose to the ipsilateral breast, were significantly lower than those of non-coplanar 3D-CRT and coplanar VMAT. The average D 2% to the contralateral breast and the V 5Gy to the contralateral lung did not differ significantly among the techniques. Furthermore, the mean prescribed MU for DWA was 486.22 MU, which was only 9.8% higher than that for non-coplanar 3D-CRT (442.67 MU) (p < 0.05).

Conclusion The use of DWA for APBI improved the dose distribution compared to that of non-coplanar 3D-CRT and coplanar VMAT; this may reduce the risk of toxicity without prolonging treatment time. PO-0838 Treatment planning for the MR-linac: plan quality compared with current clinical practice A.J.A.J. Van de Schoot 1 , C. Carbaat 1 , B. Van Triest 1 , T.M. Janssen 1 , J.J. Sonke 1 1 The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Clinical introduction of the MR-linac (MRL) involves treatment planning using Monaco (Elekta AB, Stockholm,