ESTRO 36 Abstract Book

S451 ESTRO 36 2017 _______________________________________________________________________________________________

fractions were produced using four techniques: 3D- conformal radiotherapy (CRT) wide-tangents (WT), volumetric-modulated arc therapy (VMAT) using a 'bow-tie' approach, Tomotherapy (FB only) and proton beam therapy (PBT). PBT planning incorporated a novel approach to robustness optimisation to improve comparability of proton and photon plans. The Wilcoxon- ranked sum (5% significance level) and Friedman tests (2.5% significance level to account for multiple comparisons) were used to compare dose metrics achieved by the different planning solutions. Results

beam-on time.

Results The mean equivalent doses in 2-Gy fractions to 40% (EQD40%) of the volumes of the bilateral hippocampus were for 9.90/5.31 Gy for coVMAT/VMDWAT, respectively. The EQD40% for VMWAT were < 7.3 Gy, which is the threshold predicting cognitive impairment, as defined by Gondi et al., and were significantly lower than those for coVMAT. The mean equivalent doses in 2-Gy fractions to 2, 10, 20, 30, 50, 80, 98 % (EQD2-98%) of the volumes of the bilateral hippocampus was also significantly lower than those of coVMAT. VMDWAT also significantly reduced the EQD40% and EQD2-98% of the left hippocampus. While the normal brain volume receiving 5 Gy (V5) was significantly larger in VMDWAT, as compared to coVMAT, the normal brain volume receiving 10, 15, 20, 25, 30, 35, 40, 45, and 50 Gy (V10–50) was significantly smaller in VMDWAT. The conformity and homogeneity indices were significantly better in VMDWAT. The mean treatment time of VMDWAT was significantly longer than that of to VMDWAT (67.1/70.1 seconds in coVMAT/VMDWAT, respectively).

Conclusion For most patients heart and lung doses can be minimised using a simple breath hold and wide tangent 3DCRT technique. Arc therapies were more successful in delivering higher dose to a greater proportion of the IMC, especially when combined with breath hold. Proton therapy offers excellent coverage with low OAR dose but is unlikely to be necessary in the majority of patients in whom acceptable plans can be produced using simple photon techniques. PO-0843 volumetric-modulated Dynamic WaveArc therapy reduces the doses to the hippocampus M. Uto 1 , T. Mizowaki 1 , K. Ogura 1 , Y. Miyabe 1 , M. Nakamura 1 , N. Mukumoto 1 , H. Hirashima 1 , M. Hiraoka 1 1 Kyoto University Graduate School of Medicine, Radiation Oncology and Image-Applied Therapy, Kyoto, Japan Purpose or Objective Sparing the hippocampus seems to be important for patients with brain tumors to preserve their cognitive function. Vero4DRT (Mitsubishi Heavy Industries, Ltd., Tokyo, Japan, and Brainlab, Feldkirchen, Germany) has a unique design, in which the gantry is mounted in the O- ring structure. The gantry and the O-ring can rotate at the same time, and it allows to use safe sequential noncoplanar volumetric-modulated trajectories, termed as volumetric-modulated Dynamic WaveArc therapy (VMDWAT), without a couch rotation. Since VMDWAT appears to reduce the doses to the hippocampus in patients with pituitary adenomas and craniopharyngiomas, we performed a planning study to compare the dose distribution of volumetric-modulated arc therapy using only a coplanar arc (coVMAT) and VMDWAT. Material and Methods Thirty patients were included in this study (15/15 patients with pituitary adenoma/craniopharyngioma, respectively). Contouring and treatment planning were performed using the RayStation version 7.4 (RaySearch Laboratories, Stockholm, Sweden). The Collapsed Cone calculation version 3.1 algorithm was employed. All plans were created using one arc. The prescription dose was 52.2 Gy in 29 fractions, and 99% of each PTV was covered by 90% of the prescribed dose. Optimization was performed to maximally reduce the doses to the hippocampus. The two plans were compared in terms of target homogeneity, target conformity, treatment time, the doses to the hippocampus, and the irradiated volume of normal brain. The treatment time was defined as the

Conclusion VMDWAT significantly reduced the doses to the bilateral and left hippocampus compared to coVMAT. The target conformity and homogeneity were significantly better in VMDWAT. Although the treatment time and V5 of the normal brain was increased in VMDWAT, V10–50 of the normal brain was significantly decreased in VMDWAT. VMDWAT could be a promising treatment technique for pituitary adenomas and craniopharyngiomas.