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Conventional uniform-dose IMRT plans for three patients
did not pass the clinical acceptance criteria due to the
patient geometry, particularly due to violation of rectal
dose-volume constraints. In all cases, biologically-
optimized IMRT plans were superior to other treatment
modalities on the basis of rectum and bladder NTCP. All
comparison results are summarised in Table 1. In Figure 1,
the DVH curves for one patient demonstrate the ability of
biologically optimized IMRT planning to minimize dose to
healthy tissues while maintaining a high TCP.
Conclusion
In conclusion, biological optimization of prostate IMRT
using a TCP model has the potential to improve the clinical
outcome by maximizing TCP and simultaneously
minimizing dose to normal structures. This has been
demonstrated in the context of population-based tumour
cell density distributions. Future work will include the
implementation of voxel-level patient-specific data from
multiparametric imaging which will allow a personalized
approach to IMRT planning with a dose distribution
tailored to the specific patient/tumour biology.
EP-1567 Inverse planning versus forward planning for
orbital lymphoma
E.M. Ambroa Rey
1
, A. Ramirez Muñoz
1
, D. Navarro
Jiménez
1
, R. Gómez Pardos
1
, M. Colomer Truyols
1
1
Consorci Sanitari de Terrassa, Medical Physics Unit-
Radiation Oncology Department, Terrassa, Spain
Purpose or Objective
Non-Hodgkin’s lymphoma (NHL) of the orbit is an unusual
presentation of extranodal NHL and represents 8% of all
extranodal NHL and about 1% of all NHL. The purpose of
this study is to present a dosimetric analysis between
inverse and forward plans for mucosa associated
lymphoid tissue (MALT) lymphoma.
Material and Methods
Three patients diagnosed with MALT lymphoma were
analyzed. Three types of plans (3DCRT, IMRT and VMAT)
were created for each
patient.
The whole orbital volume was included in the CTV. The
organs at risk (OAR), right and left eye, right and left lens,
right and left optical nerve, were contoured. Prescription
was 27 Gy at 1.8 Gy per
fraction.
The 3DCRT plans were elaborated using the treatment
planning system (TPS) XiO version 5.1. Five isocentric
beams were used. Inverse plans calculations (IMRT and
VMAT) were carried out using the Monaco TPS version
5.10. IMRT plans were created based on a five-field
arrangement and dynamic MLC delivery method. For VMAT
plans, two partial arcs were used. For every plan, the
following data for the PTV was recorded: V95%, D50%,
D98%, D2%, CI, HI, MU, number of segments and estimated
delivery time. For the principal organs at risk, such as the
optical nerve, contralateral eye and contralateral lens,
the maximum and mean dose were reported.
Results
Table I summarizes the results for the PTV.
Inverse planning improves PTV coverage in comparison
with forward planning. Also the near-minimum dose D98%
is higher for IMRT and VMAT than 3DCRT. In addition the
near-maximum dose D2% is lower for IMRT and VMAT. In
terms of conformity, the three plans have similar results;
meanwhile the 3DCRT technique has a worst homogeneity
index. VMAT treatment plans reduce the monitor units and
number of segments in comparison with the IMRT plans.
For the OAR, the maximum dose (mean value) to the
contralateral lens was 4.30Gy for the 3DCRT plans; 3.33Gy
for IMRT and 2.86Gy for VMAT plans. For the left optical
nerve the maximum dose was 9.39Gy for 3DCRT; 7.31Gy
for IMRT and 6.96Gy for VMAT, and for the left eye was
7.20Gy for 3DCRT; 6.37Gy for IMRT and 5.16Gy for VMAT.
Dose distribution (axial view) for one representative
patient
is
shown
in
Fig
I.
Conclusion
According to the results, we can conclude that inverse
planning is feasible for MALT orbital lymphoma treatment,
providing excellent dose coverage of target volume and
reduces dose to the organs at risk. Furthermore, we can
establish that in terms of coverage and sparing OAR, IMRT
and VMAT techniques are very similar, but VMAT technique
achieves a faster delivery treatment, resulting in a lower
probability of patient movement during the treatment.
Despite the fact that the number of examined patients is
low, we are sure that inverse planning is an improvement
for every patient with this type of malignance, but further
investigations, with more cases, between IMRT and VMAT
should be done.
EP-1568 Benefit of a breath hold radiotherapy
technique for breast and internal mammary nodes
irradiation
F. Jouyaux
1
, A.L. Blin
1
, I. Lecouillard
1
, M. Benchalal
1
, C.
Lafond
1,2,3
1
Centre Eugène Marquis, Radiotherapy, Rennes CEDEX,
France
2
Rennes 1 University, LTSI, Rennes, France
3
INSERM, U1099, Rennes, France
Purpose or Objective
Loco-regional radiotherapy of left-sided breast cancer
represents a treatment planning challenge when the
internal mammary lymph nodes (IMN) are included in the
target volume because of high radiation exposure to the
heart. This planning study aimed to quantify the reduction