ESTRO 36 Abstract Book

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S828 ESTRO 36 2017
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node irradiation. This study intends to determinate the
incidental coverage and dose distribution of the internal
mammary chain in breast cancer treatment, using
tangential and opposite fields with 3D External
Radiotherapy.
Material and Methods
We randomly reviewed 47 female patients treated at one
institution between January and December of 2013 with
an average age of 62 years. Thirty seven patients (78%)
had invasive ductal carcinoma (IDC), and 10 patients
(21.2%) other histology types; Her2: Negative (82%),
hormonal receptors were positive in all of them, 30
affecting the left and 17 the right breast. The majority of
tumours were <2cm (n:41/47). Lumpectomy + Sentinel
node biopsy (SLN) was performed in 36 patients, one of
them with posterior axillary lymph node dissection due to
positivity of SNL and the remaining patients were
candidates for axillary lymph node dissection. External
radiotherapy was administrated exclusively on the breast
with tangential and opposite fields with total dose: 50Gy
in 5 weeks with 5 fractions per week (200cGy per
fraction). Once the treatment was completed, we contour
the internal mammary chain according to the Breast Atlas
for radiation therapy planning consensus definitions of the
RTOG.
Results
With an average volume of the internal mammary chain of
4.13 cm3, the median minimal dose and maximal dose
delivered was 278cGy and 4008cGy respectively, this last
one corresponding to 8% of Total dose prescribed for the
mammary gland. The median V95 was 297.04cGy.
Conclusion
The radiation of the internal mammary chain on patients
of this study have showed minimal incidental doses,
therefore we concluded that the contouring, volume
delimitation and dose prescription has been appropriated
by not affecting unwanted areas. In the other hand
unintended radiation of internal mammary chain turns out
as insufficient to treat subclinical disease.
EP-1559 Optimizing the risks for deterministic effects
and secondary malignancies in bladder and rectum
G. Komisopoulos1, C. Buckey2, S. Stathakis3, M.
Mavroeidi4, G.P. Swanson5, D. Baltas6, N. Papanikolaou3,
P. Mavroidis4
1 University Hospital of Larissa and General Hospital of
Larissa- Greece, Medical Physics, Larissa, Greece
2 Mayo Clinic- AZ, Radiation Oncology, Scottsdale, USA
3 University of Texas Health Sciences Center at San
Antonio, Radiation Oncology, San Antonio- TX, USA
4 University of North Carolina, Radiation Oncology,
Chapel Hill, USA
5 Baylor Scott & White Healthcare Temple Clinic,
Radiation Oncology, Temple- TX, USA
6 University of Freiburg & German Cancer Consortium
DKTK- Partner Site, Radiation Oncology-, Freiburg,
Germany
Purpose or Objective
To use radiobiological metrics to estimate the
effectiveness of IMRT and Conformal Radiation Therapy
(CRT) modalities in treating prostate tumors. Additionally,
to estimate the risk of secondary malignancies in bladder
and rectum due to radiotherapy from these treatment
modalities.
Material and Methods
For ten prostate cancer patients, IMRT and CRT plans were
developed. For the IMRT plans, two beam energies (6 and
18 MV) and two treatment protocols were used (RTOG
0415 and FCCC). For the evaluation of the deterministic
effects of these plans, the tumor control probabilities
(TCP) and normal tissues complication probabilities
(NTCP) were calculated using the LQ-Poisson and Relative
Seriality models. Additionally, the complication-free
tumor control probability and the biologically effective
uniform dose were calculated for each plan. The risks for
secondary malignancies were calculated for bladder and
rectum for the different treatment modalities using the
LQ model proposed by UNSCEAR.
Results
The deterministic response probabilities of bladder were
lower than those of rectum in all the plans. For bladder,
the highest value was for the IMRT FCCC-18X (0.03%) and
the lowest for the CRT-18X modality (0.0%). For rectum,
the highest value was for the IMRT RTOG-6X (3.52%) and
the lowest for the IMRT FCCC-18X modality (0.41%).
The average risk for secondary malignancy was lower for
bladder (0.37%) compared to rectum (0.81%) based on all
the treatment plans of the ten prostate cancer patients.
The highest average risk for secondary malignancy for
bladder and rectum was for the CRT-6X modality (0.46%
and 1.12%, respectively) and the lowest was for the IMRT
RTOG-18X modality (0.33% and 0.56%, respectively).
Fig. 1 shows the dose-responses of bladder and rectum for
a range of uniform doses for the different radiation
modalities. Additionally, the average response of each
modality is plotted accompanied by error bars indicating
the standard deviations of response and dose within the
patient group. In Fig. 2, the average distributions of the
risk for secondary malignancy in bladder (upper) and
rectum (lower) as a function of dose are presented for the
different modalities and protocols. The vertical lines
indicate the mean doses that are delivered to the bladder
and rectum by the examined treatment plans. The thick
solid line corresponds to uniform irradiation of the organ.
Conclusion
IMRT plans produced using the RTOG 0415 criteria had
equivalent dosimetric results with the CRT plans. General
constraints seem suboptimal for sparing rectum when
using IMRT. However, tighter dose constraints may result
in higher dose inhomogeneities in the PTV. The treatment
modalities that had lower NTCP values were inferior in
many cases regarding the risk for secondary malignancies.
Consequently, the optimization of different treatment
modalities and plans should be complemented by the
estimation of the corresponding risks for developing
secondary malignancies.
EP-1560 Left breast cancer planning with VMAT
technique: the dosimetric trade-offs
A. Fogliata1, J. Seppala2, G. Reggiori1, F. Lobefalo1, V.
Palumbo 1, F. De Rose1, D. Franceschini1, M. Scorsetti3, L.
Cozzi 3
1Humanitas Research Hospital, Radiation Oncology,
Milan-Rozzano, Italy
2Kuopio University Hospital, Cancer Center, Kuopio,
Finland
3Humanitas Cancer Center and Humanitas University,
Radiation Oncology, Milan-Rozzano, Italy
Purpose or Objective
: Intensity modulation with volumetric modulated arc
therapy (VMAT) for breast cancer treatment has been
explored, proving that, as a trade-off of improved target