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Conclusion
Even though the analyzed IGRT protocol focuses entirely
on the gold seed of the prostate the needed margins for
the lymph nodes are only slightly larger than 5 mm which
in many centers are used as a standard PTV margin. Thus,
the additional margin needed to include the lymph nodes
is actually somewhat modest. However, the optimal
balance between dose coverage of tumor and lymph nodes
both in regard to local control and toxicity is still unclear,
and needs further investigation.
PO-0836 Impact of Deep Inspiration Breath Hold on
Left Anterior Coronary dose in Left Breast irradiation.
F. Azoury
1
, S. Achkar
1
, N. Farah
1
, D. Nasr
1
, C. El Khoury
1
,
N. Khater
1
, J. Barouky
1
, R. Sayah
1
, E. Nasr
1
1
Hotel Dieu de France Hospital - Saint Joseph University,
Radiation Oncology, Beirut, Lebanon
Purpose or Objective
Irradiation of Left breast cancer exposes women to higher
doses to the heart and LAD coronary. Blocking the heart in
the tangent fields will inevitably cause under dosage in
proximity to the tumor bed. Here we evaluate the effect
of deep inspiration breath hold (DIBH) on the coverage of
the whole breast and the reduction of heart and LAD
doses.
Material and Methods
We performed a dosimetric study on 25 patients treated
with DIBH for left breast cancer utilizing RPM (Varian
Medical Systems). Treatment plans were generated in Free
Breathing (FB) and DIBH. Optimization was done with 3D
Field-in-Field technique utilizing two-tangent setup. Care
was taken to cover the whole breast volume. Prescription
dose was 50Gy in 25 fractions. Planning objectives were:
near minimum dose (D98) > 90% (45Gy), near maximum
dose (D2) <105% and a median dose of 50Gy. Doses to the
heart, LAD and left lung were compiled, left breast
coverage was evaluated, and statistical analysis was
performed using Student T-test with a 95% Interval of
confidence.
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