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Results
Left breast results: Identical coverage was achieved with
a D95 of 95.2% ±0.4 (DIBH) vs. D95= 95.4%±0.6
(FB)(p=0.27). No statistical difference were found in D98,
median and D2 (Figure1.A). Left lung results: No statistical
difference was also found (Figure1.B). Heart results: Doses
were significantly lower with DIBH; Dmean at 1.5Gy±0.8
(DIBH) vs. 2.9Gy±1.6 (FB) (p<0.001) and Dmax at
36.3Gy±14.7 (DIBH) vs. 46.2Gy±6.6 (FB) (p=0.004). DVH
metrics for V10, V20, V30, and V40 were all significantly
better in DIBH (Figure1.C). LAD coronary results: Doses
were significantly lower with DIBH with Dmean at 9.5Gy ±
7.2 (DIBH) vs. 21.8Gy±11.4 (FB) (p<0.001) and a Dmax at
29.2Gy±17 (DIBH) vs. 42.3Gy±12 (FB) (p=0.003). DVH
metrics favored the DIBH plans significantly all across the
range of doses (Figure.1D).
Conclusion
In the treatment left breast cancer, 3D-DIBH showed
superior dosimetric advantages in comparison to 3D-FB.
Both heart and LAD were significantly spared without
compromising left breast coverage. The LAD was spared
for doses ranging from the low dose spectrum to the
highest dose.
PO-0837 Dosimetric advantages afforded by Dynamic
WaveArc therapy accelerated partial breast irradiation
Y. Ono
1
, M. Yoshimura
1
, K. Hirata
1
, N. Mukumoto
1
, T.
Ono
1
, M. Inoue
1
, M. Ogura
1
, T. Mizowaki
1
, M. Hiraoka
2
1
Kyoto University- Graduate School of Medicine,
Department of Radiation Oncology and Image-applied
Therapy, Kyoto, Japan
2
Japanese Red Cross Wakayama Medical Center,
Department of Radiation Oncology, Wakayama, Japan
Purpose or Objective
We identify dosimetric advantages of the novel volumetric
modulated arc therapy (VMAT) featuring continuously
varying non-coplanar trajectories. This is the Dynamic
WaveArc (DWA) therapy used for accelerated partial
breast irradiation (APBI). The dose distribution of DWA
therapy was compared to that of non-coplanar three-
dimensional conformal radiotherapy (3D-CRT) and
coplanar VMAT.
Material and Methods
We evaluated APBI dose distributions, delivered via DWA,
in 24 left-side breast cancer patients via non-coplanar 3D-
CRT from November 2011 to April 2016 at our institution.
The prescribed dose was 38.5 Gy in 10 fractions. The
Vero4DRT enables DWA by continuous gantry rotation and
O-ring skewing with moving dynamic multi-leaf collimator
(MLC). Thus, the Vero4DRT delivers non-coplanar VMAT
without couch rotation, minimizing dose delivery to
adjacent organs at risk (OARs). We created two sets of 11
control points (at angles 315-35° to the O-ring angle, and
110-155° and 290-355° to the gantry angle), for two non-
coplanar DWA trajectories. DWA, non-coplanar 3D-CRT,
and coplanar VMAT treatment plans were created by a
clinical treatment planning system, Raystation, using a
collapsed cone dose-calculation algorithm (Figure 1-A).
The mean DWA doses to the planning target volume (PTV),
the bilateral breasts, the lungs, the heart, the left
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).