ESTRO 36 Abstract Book

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S633 ESTRO 36
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EP-1164 Improved accuracy in IORT with electron
beams by a new measuring system of mammary gland
thickness
P. Scalchi1, A. Marchesin2, G. Scalco2, S. Bacchiddu3, C.
Mari3, L. Grandin3, P. Francescon1, F. De Marchi2, C.
Baiocchi3
1 Ospedale San Bortolo, MEDICAL PHYSICS, Vicenza, Italy
2 Ospedale San Bortolo, SURGERY, Vicenza, Italy
3 Ospedale San Bortolo, RADIOTHERAPY, Vicenza, Italy
Purpose or Objective
In IORT of the breast cancer using electron beams (IOERT),
the beam energy should be properly chosen, as
recommended by both ICRU 71 (2004) and AAPM TG72
(2006), to ensure that the entire PTV be covered by the
90% of the maximum dose (D max) and the ICRU reference
point be positioned as near as possible to D max. Due to the
physical characteristics of these beams, the measurement
of the mammary gland thickness can be critical. In fact,
usually it is measured before docking using a needle and a
ruler ('needle method”), or ultrasounds. Nevertheless the
measured thickness can differ from the real one after
docking completion, thus affecting the accuracy of the
subsequent dose release. To allow accurate
measurements of the gland thickness under treatment
conditions, a new measurement system (MARK's) was
developed at Vicenza Hospital. The aim of this work is to
compare the needle method to MARK's in terms of surgeon-
surgeon variability and dosimetry impact.
Material and Methods
A mobile IOERT-dedicated linac (LIAC,SIT) with four
electron energies (4 to 10 MeV) is used at Vicenza
Hospital. MARK’s is a sterilizable manual pointer with
integrated ruler. After radioprotective disk positioning,
the surgeon stitches the mammary gland to prepare the
PTV. Then he inserts the terminal part of the applicator,
after applying a thin patch layer underneath to prevent
target herniation and, while keeping it pressed, he inserts
the pointer inside the applicator allowing direct thickness
measurements in treatment conditions.
14 patients were studied. The measurements were taken
first by the needle method, and then by MARK's. Five
measurements points were always taken, one at the
center of the PTV and four marginal positions (cranio-
caudal and lateral). The electron energies were chosen
based on the resulting thickness. The two systems were
compared in terms of both the choice of the electron
energy, as resulting by following ICRU and AAPM
recommendations, and the surgeon-surgeon variability.
Results
As shown in the following Table, the needle method
systematically overestimates the PTV thickness and
surgeon-surgeon reproducibility is better for MARK’s.
Following ICRU71 and AAPM TG72 the needle method
would cause 11 erroneous energy choices and 5 treatments
to be wrongly canceled.
N. of
erroneous
energy
choices
(needle
method)
N. of
possible
treatment
cancelations
following
ICRU 71 and
AAPM TG 72
(needle
method)
Surgeon-
surgeon
variability
(needle
method)
Surgeon-
surgeon
variability
(MARK's)
Thickness
difference
between
methods
11 5 2 mm 1 mm
0.0 ÷ 20.0
mm (5.4
mm on
the
average)
Conclusion
A new system for measuring the mammary gland thickness
prior to IOERT developed at Vicenza Hospital was
compared to a traditional needle method. The former
shows better reproducibility and accuracy, because it
reproduces the same target thickness as it exists after the
docking. Regarding both treatment decisions and
dosimetric accuracy, the found differences are critical
when the international recommendations are followed.
EP-1165 Short and long term safety of a post-
mastectomy conformal electron beam radiotherapy
(PMERT)
N. Grellier-Adedjouma1, M. Chevrier2, H. Xu1, N.
Fournier-Bidoz1, F. Campana1, F. Berger 2, A. Fourquet1,
D. Peurien1, D. Lefeuvre2, Y.M. Kirova1
1Institut Curie, Radiation Oncology, Paris, France
2Institut Curie, Statistics, Paris, France
Purpose or Objective
To evaluate short and long-term safety of a chest wall
irradiation after mastectomy with our previously
published PMERT technique, depending on patient
characteristics and treatments received.
Material and Methods
We included all women irradiated after mastectomy for a
non-metastatic breast cancer with PMERT between 2007
and 2011 in our Department of Radiation Oncology. Acute
and late toxicities (CTCAE v3.0) were evaluated with a
weekly clinical examination during irradiation and then
with monitoring consultations at least every 6 months. We
also conducted a dosimetric analysis of 100 consecutive
patients irradiated on the chest wall and lymph nodes (LN)
(50 right and 50 left), to assess the doses to organs at risk.
Results
Among the 796 women included, mean age was 53.2 years
(22.1-90.8), 47.6% of them had at least one cardiovascular
risk factor, regardless of age, 49% were post menopausal,
8.3% were obese (BMI ≥ 30) and 6.9% and 11.9% had cardiac
and pulmonary comorbidities respectively.
Internal mammary chain (IMC) was irradiated in 85.6% of
cases, supra, infraclavicular LN and axilla in 88.3%, 77.9%
and 14.9% of cases. Mean chest wall dose was 49.4Gy (39-
56) over 40 days (30-119). Energies of 6 and/or 9 MeV were
used in 84.7% of cases.
The maximum acute skin toxicity was grade 1 in 58.5% of
patients, grade 2 in 35.9%, and grade 3 in 4.5% of them.
There was no grade 4 toxicity. Concomitant chemotherapy
was associated with an increased risk of grade 3 toxicity
(p <0.001).
With an median follow up of 64.1 months (5.6-101.5),
29.8% of patients had, temporarily or permanently,
hyperpigmentation, fibrosis or telangiectasia (grade 1:
23.6%, grade 2: 5.2%, grade 3: 1%), which tended to be
promoted by smoking (p = 0.06); 274 patients (34.4%)
underwent breast reconstruction, on average 19.7 months
after the end of irradiation (3.6-86.8), which was