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S508
ESTRO 36 2017
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Purpose or Objective
Locally advanced tumors with conservative surgery have a
higher relapse rate than early tumors. We analyze the
clinical outcome of HDR brachytherapy boost in patients
at high risk for tumor size, in terms of local control,
adverse effects and cosmetic results.
Material and Methods
Between February 1999 and October 2011, forty two
patients with 43 tumours, consecutively diagnosed with
cT3 infiltrative breast carcinoma were treated with
neoadjuvant systemic treatment, conservative surgery
and Whole Breast Irradiation (WBI) (50 Gy) followed by
High Dose Rate (HDR) interstitial brachytherapy boost (3 x
4.4 Gy at 85% isodose) in two days, with rigid needles.
Survival rates were calculated using the Kaplan-Meier
method, and the Cox proportional hazards model to
demonstrate the infuence of tumor response to
neoadjuvant chemotherapy.
Results
Median age was 48 years (30-77). Median follow-up was 95
months (8-201). The average lesion size was 56.7 mm (50-
100) before receiving any treatment. Local Control (LC) at
5 and 10 years was 87.1%. Overall Survival (OS) at 5 and
10 years was 85.7% and 72.4% respectively. Cancer-
Specific Survival (CSS) to 5 and 10 years was 85.7% and
75.8%. Disease-Free Survival (DFS) was 74,4% and 62,7% at
5 and10 respectively. Twenty-five tumor lesions (58 %) had
a complete response after neoadjuvance. There were no
significant differences in terms of local control depending
on the tumor response to neoadjuvant chemotherapy (p =
0.66). Nor concerning overall survival (p = 0.52) or cancer-
specific survival (p = 0.74). Grade 1 early toxicity was
38.5% and Grade 2 was 12.8%. There were no early Grade
3-4 toxicity. For late toxicity, 7/43 (16.3%) of patients had
fibrosis. Some of the patients reported induration from
surgery. There were no trophic skin changes. Good or
excellent cosmesis was recorded in 95.3% of patients.
Conclusion
Adding HDR brachytherapy boost to conserving therapy
allows preservation of breast in 87% of locally advanced
breast tumors (cT3) at 10 years, with good cosmetic
outcome.
This technique is effective and well tolerated.
PO-0925 Timing of post-implant analysis in permanent
breast seed implant: results from a serial CT study
E. Watt
1
, M. Peacock
2
, L. Conroy
1
, S. Husain
3
, A.
Frederick
1
, M. Roumeliotis
3
, T. Meyer
3
1
University of Calgary, Department of Physics &
Astronomy, Calgary- Alberta, Canada
2
University of British Columbia, Division of Radiation
Oncology, Vancouver- British Columbia, Canada
3
University of Calgary, Department of Oncology, Calgary-
Alberta, Canada
Purpose or Objective
Permanent breast seed implant (PBSI) is a novel, one-day
procedure for the treatment of early-stage breast cancer.
In this technique, stranded
103
Pd seeds are permanently
implanted in a volume surrounding the post-lumpectomy
seroma. Post-implant dosimetry is used to assess implant
quality, but the timing for this analysis is performed
inconsistently across cancer centres. The use of different
time points for analysis limits the ability to combine
results for long-term outcome studies. The purpose of this
study is to determine the most appropriate timing for
post-implant dosimetry.
Material and Methods
Ten patients underwent CT scans at 0 (immediately after),
15, 30, and 60 days post-implant. Each post-implant CT
scan was deformably registered to the planning scan to
obtain the seroma contour (clinical target volume, CTV)
using MIM Maestro
TM
(MIM Software, Inc., Cleveland OH).
This contour was reviewed and adjusted as necessary by a
radiation oncologist. Using the TG-43 dose calculation
formalism, a postplan was generated for each scan. For
comparison, a model of the total accumulated dose to the
target was calculated by summing the dose contributions
from each time point. This was accomplished by
deformably registering each post-implant CT scan and
associated dose to the day 0 CT scan, scaling the dose
contribution according to the seed activity at the time of
the scan. A dose evaluation volume (DEV) was defined on
all scans as a 5 mm isotropic expansion of the CTV trimmed
to skin and chest wall muscle. Dosimetric indices for the
CTV (V100) and DEV (V90, V100, and V200) were compared
between each individual postplan and the accumulated
dose using either a paired t-test or a Wilcoxon signed rank
test, whichever carried more power given the distribution
of the data. Residuals were also calculated, defined as the
difference in dosimetric indices for a given time point and
the accumulated dose model. As either a positive or a
negative residual represents a deviation from the model,
the median of the errors (where each error is the absolute
value of the residual) was also calculated for each time
point.
Results
The residuals for the DEV V100 and V200 for all 10 patients
at each time point are shown in Figures 1 and 2,
respectively. A statistically significant difference was
observed between the day 60 scan and the accumulated
dose for the DEV V90, V100, and V200 (paired t-test); no
other significant differences were found. The smallest
median (range) error occurred for the day 15 CT scan (as
demonstrated in Figures 1 and 2); 2.4% (0.2-7.3%) and 4.5%
(0.6-15.9%) for the DEV V100 and V200, respectively.
Conclusion
The results of this study indicate that the day 15 scan is
the most representative of the accumulated dose
delivered to target volumes in PBSI. For a 10-patient
cohort, the median error was found to be at a minimum
for the DEV V100 and V200 for the day 15 time point when
compared to the day 0, 30, and 60 scans.