470 / 1096
S455
ESTRO 36
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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.
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
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