ESTRO 36 Abstract Book

S455 ESTRO 36 _______________________________________________________________________________________________

were 0.22 for “Standard” plans, 0.19 for “SRR” plans, 0.18 for “Model” plans and 0.17 for “Model + SRR” plans. Plans “Model + SRR” showed slightly less dose homogeneity: mean homogeneity indexes varied from 0.077 for “standard” plans to 0.101 for “Model + SRR” plans. Dose conformity was very similar for all plans: the conformal index varied of 1% in average. “Model + SRR” plans required an increase of 22% in the number of MU compared to the “Standard” plan. The irregularity and modulation indexes increased of 58% and 10%, respectively.

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

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 Compared to standard prostate VMAT plans, applying specific dose constrains to the SRR and rectal wall using the “Moore method” should decrease of around 8 Gy the mean dose to the SRR and decrease relatively of 23% the risk of rectal bleeding. PO-0842 Choosing the best heart sparing technique for breast and internal mammary chain radiotherapy A. Ranger 1 , A. Dunlop 1 , K. Hutchinson 2 , M. Maclennan 3 , H. Convery 4 , H. Chantler 2 , C. Rose 2 , N. Twyman 2 , E. Donovan 1 , E. Harris 5 , C. Coles 2 , A. Kirby 6 1 The Royal Marsden NHS Trust and The Institute of Cancer Research, Physics, London, United Kingdom 2 Cambridge University Hospitals NHS Trust, Physics, Cambridge, United Kingdom 3 Lothian and Dumfries NHS Trust, Oncology, Edinburgh, United Kingdom 4 The Royal Marsden NHS Trust, Physics, London, United Kingdom 5 The Institiute of Cancer Research, Physics, London, United Kingdom 6 The Royal Marsden NHS Trust and The Institute of Cancer Research, Clinical Oncology, London, United Kingdom Purpose or Objective Published data demonstrate a 4.4% overall survival benefit t associated with inclusion of the internal mamm ary chain (IMC) in the radiotherapy (RT) target volume in patients with breast cancer. Survival gains will be maximised by minimising radiation doses to heart and lungs. This dosimetry study compares the ability of breath-hold techniques in 3D conformal radiotherapy, arc therapy and protons to achieve target volume constraints whilst minimising dose to heart and lungs with a view to defining implementable class solutions for irradiating the IMC. Material and Methods Breast tissue, level I-IV axillary and IMC lymph nodes were outlined using ESTRO consensus guidelines in 14 patients scanned in both free breathing (FB) and breath hold (BH). Seventy two locoregional RT plans, prescribed to 40Gy/15