ESTRO 36 Abstract Book

S451

ESTRO 36 2017

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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

, T. Mizowaki

, K. Ogura

, Y. Miyabe

, M.

Nakamura

, N. Mukumoto

, H. Hirashima

, M. Hiraoka

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

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

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.