1015 / 1096
S999
ESTRO 36
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Purpose of this study was to compare the dose distribution
to the organs at risk for different longitudinal margins
using a DVH- and NTC-based approach.
Material and Methods
10 patients with SCC of the middle or the lower third, who
underwent CRT at our institution were retrospective
selected. Three planning target volumes (PTV) were
created for every patient, with an axial margin of 1.5 cm
to the gross target volume (GTV) (primary tumor and PET-
positive lymph nodes), analogous to the protocol of the
CROSS-trial. The longitudinal margins were 4 cm, 3 cm and
2 cm, respectively. Contouring and treatment planning
was performed with the Eclipse 13 planning system (Varian
Medical Systems, Palo Alto, CA, USA). For every PTV,
volumetric modulated arc therapy (VMAT) plans were
optimized. Dose calculation was performed using the AAA
algorithm (version 10.0.28) and heterogeneity correction.
All plans were normalized to a median prescribed PTV dose
of 41.4 Gy with a daily dose of 1.8 Gy. Dose to the lungs,
heart and liver were evaluated and compared. Differences
of dose parameters were tested for significance with t-
test for paired samples.
Results
Median tumor length was 6 cm with a range of 3 to 10 cm
and 8 of the 10 patients (80%) had lymph node metastasis.
When using a longitudinal margin of 3 cm instead of 4 cm,
all dose parameters (Dmin, Dmax, Dmean, Dmedian and
V5-V35), except Dmax could be significantly reduced for
the lungs. Regarding the heart, a significant reduction was
seen for Dmean and V5, whereas no significant difference
was seen for Dmin, Dmax, Dmedian and V10-V35. When
comparing a longitudinal margin of 4 cm to a longitudinal
margin of 2 cm, not only Dmin, Dmax, Dmean, Dmedian
and V5-V35 for the lungs, but also Dmax, Dmin and V5-V35
for the heart were significantly reduced. Nevertheless, no
difference was seen for the median heart dose. In
addition, the risk of pneumonitis was significantly reduced
by a margin reduction of 3 cm and 2 cm.
Conclusion
The reduction of the longitudinal margin from 4 cm to 3
cm can significantly reduce the dose to lungs, while the
reduction to 2 cm can also reduce doses to the heart.
Despite clinical benefit and oncologic outcome remain
unclear, reduction of the longitudinal margins might
provide the opportunity to reduce side effects of CRT for
SCC in upcoming studies.
EP-1824 Elective breast RT including level I & II
lymph nodes: A planning study with the humeral head
as PRV
J. Van der Leer
1
, K. Surmann
1
, M. Van der Sangen
1
, M.
Van Lieshout
1
, C.W. Hurkmans
1
1
Catharina Ziekenhuis, Radiotherapy, Eindhoven, The
Netherlands
Purpose or Objective
The aim of this planning study was to determine a new
technique for elective breast radiotherapy and level I and
II lymph nodes following the new ESTRO delineation
consensus guidelines. According to these guidelines the
humeral head should be spared by introducing a planning
risk volume (PRV) of the humeral head and connective
tissue 10 mm around it.
Material and Methods
We included ten left sided breast cancer patients in our
planning study in Pinnacle
3
v9.8. Each patient was planned
with 16 x 2.66 Gy on the breast PTV (PTVp) and the
elective level I and II lymph nodes (PTVn).
We compared three treatment planning techniques: high
tangential field (HTF), 6-field IMRT and VMAT. The HTF
technique consisted of two open beams with extra
segments and the cranial and posterior border was
extended to include PTVn. Some of the leaves were closed
to spare the humeral head + 10 mm around it (hh+10). For
the IMRT technique we added four additional fields to the
high tangential fields (gantry angle of 330, 30, 80 and 170
degrees) to ensure coverage of the cranial part of the
breast and lymph nodes. The caudal border of these
additional fields was set 1 cm below the attachment of the
clavicle at the sternum. The third technique was a dual
arc VMAT from 305 to 180 degrees.
The plans were made by inverse planning, achieving a
PTVp coverage of V95% ≥ 97% and a PTVn V90% ≥ 95%.
Additionally, the dose to the lungs, heart and right breast
(OARs) has been minimized. hh+10 was included with an
objective of V40Gy < 1 cm
3
for all three techniques.
Results
HTF resulted in an average PTVp V95% of 97.2% and an
average PTVn V90% of 90.4% (see Table 1 and Figure 1).
With the additional fields of the IMRT technique the
coverage of PTVn increased significantly to on average 98%
(p=0.01) while PTVp did not vary significantly (p=0.92).
The dose to the OAR was comparable between the HTF
and IMRT techniques. When using VMAT the coverage of
the PTVn was on average 99.5% (p<0.01 compared to the
HTF and p=0.19 compared to IMRT). The dose to the OARs
however increased as well. The mean dose to the
contralateral breast increased significantly from 0.6 Gy
with HTF and IMRT to 2.3 Gy with VMAT (p<0.01 for both).