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ARTICLE IN PRESS
Clinical Oncology (2007) jj: jjjejjj
doi:10.1016/j.clon.2007.05.002
Original Article
An Atlas of the Pelvic Lymph Node Regions to Aid
Radiotherapy Target Volume Definition
A. Taylor*, A. G. Rockally, M. E. B. Powell*
*Department of Radiotherapy, St Bartholomew’s Hospital, London, UK; yDepartment of Radiology,
St Bartholomew’s Hospital, London, UK
ABSTRACT:
Aims: The implementation of advanced three-dimensional radiotherapy planning techniques requires accurate target
volume localisation. We have previously developed guidelines to aid definition of the pelvic lymph node regions, and the
aim of this study was to produce a CT atlas.
Materials and methods: The guidelines were applied to a CT scan of a patient to receive adjuvant radiotherapy.
Results: Reference CT images of the pelvis were generated, illustrating the nodal regions and a typical target volume for
adjuvant pelvic radiotherapy for gynaecological cancer.
Conclusion: These images can be used as an aid for target volume definition of the pelvic nodal regions. Taylor, A. et al.
(2007). Clinical Oncology jj, jej
ª 2007 Published by Elsevier Ltd on behalf of The Royal College of Radiologists.
Key words: Clinical target volume, conformal radiotherapy, intensity-modulated radiotherapy, iron oxide particles, pelvic lymph nodes,
radiotherapy planning
Introduction
Accurate and reproducible delineation of target volumes is
essential for effective three-dimensional radiotherapy.
Pelvic lymph node irradiation has an important role in the
management of many pelvic malignancies. Planning studies
comparing intensity-modulated radiotherapy (IMRT) with
conventional approaches have shown significant dosimetric
advantages in gynaecological and urological cancer [1e3].
However, one of the factors limiting widespread implementation of the technique has been a lack of consensus on
the target volume.
The probability of lymph nodes containing metastases is
currently assessed using size criteria with computed
tomography or magnetic resonance imaging (MRI). A nodal
maximal short axis diameter of greater than 10 mm
indicates a high risk of metastatic involvement, but the
sensitivity of this method is only 40e70% [4e6]. Unenlarged
nodes may still contain tumour deposits and it is therefore
necessary to include all lymph nodes within the draining
regions of the tumour in the clinical target volume (CTV).
Most ‘normal size’ lymph nodes are too small to be directly
visualised with standard imaging and delineation of the
nodal CTV depends on their relationship to other pelvic
structures.
Anatomical studies have shown that pelvic lymph nodes
lie adjacent to the major pelvic blood vessels. These are
relatively well visualised on conventional imaging and can,
with an appropriate margin, be used as a surrogate target
0936-6555/07/000000þ09 $35.00/0
for lymph nodes. Ultra-small particles of iron oxide (USPIO)
are a novel class of MRI contrast agent that make lymph
nodes more readily visible [7,8]. We have previously
reported a study with USPIO that assessed the position of
the pelvic lymph nodes in relation to the blood vessels, and
developed guidelines for outlining the lymph node regions
[9]. These guidelines have been independently applied to
a further series of patients and found to be effective in
ensuring target volume coverage for O99% of nodes [10].
The purpose of this study was to use the guidelines to
develop a generic computed tomography atlas showing the
position of pelvic lymph nodes that could then be applied
for three-dimensional radiotherapy planning techniques.
Materials and Methods
Radiotherapy planning computed tomography was used in
a patient who was to receive postoperative radiotherapy to
the pelvis, having previously undergone a simple abdominal
hysterectomy and bilateral salpingo-oophorectomy for uterine cancer. The patient was scanned in the supine position
with a full bladder, with 5 mm slice intervals from 2 cm above
the aortic bifurcation to the lower limit of the inguinal
region. Intravenous contrast was given to aid visualisation of
the blood vessels. The images were transferred to a radiotherapy planning system (Eclipse v6.5, Varian).
Using pelvic blood vessels as a surrogate target for lymph
nodes, our guidelines for delineation were applied (Table 1).
First, a 7 mm margin was drawn around the pelvic blood
ª 2007 Published by Elsevier Ltd on behalf of The Royal College of Radiologists.
Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002
ARTICLE IN PRESS
2
CLINICAL ONCOLOGY
Table 1 e Summary of the guidelines for delineating nodal
regions
Lymph node group
Common iliac
External iliac
Internal iliac
Obturator
Pre-sacral
Recommended margins*
7 mm margin around vessels. Extend posterior
and lateral borders to
psoas and vertebral body
7 mm margin around vessels. Extend anterior
border by a further 10 mm anterolaterally
along the iliopsoas muscle to include the
lateral external iliac nodes
7 mm margin around vessels. Extend lateral
borders to pelvic side wall
Join external and internal iliac regions with
a 17 mm wide strip along the pelvic side wall
Subaortic: 10 mm strip over anterior sacrum
Mesorectal: cover entire mesorectal space
*Also include any visible nodes.
vessels. The following modifications were then made: in the
common iliac region, the contour was extended posteriorly
to the vertebral body, passing around the psoas muscle; to
encompass the obturator region, the contours around the
external and internal iliac vessels were joined to create
a single volume on each side of the pelvis, ensuring that
the width was at least 17 mm from the pelvic side wall;
the upper pre-sacral region was covered with a 10 mm strip
over the anterior sacral prominence; where the margin
passed over muscle or bone, these structures were deleted
from the CTV; and finally, to cover the distal lateral external
iliac nodes, the volume was extended anterolaterally by
a further 1 cm along the line of the iliopsoas muscle. The
parametria and vaginal vault were also outlined as a separate
structure.
Reference images were produced showing the typical
target volume for adjuvant pelvic radiotherapy, including
the common iliac, anterior and medial external iliac,
internal iliac, obturator and the subaortic pre-sacral lymph
node groups.
Results
The reference images produced by applying the guidelines
are shown in Fig. 1. The typical target volume for adjuvant
pelvic radiotherapy in gynaecological cancer has been
outlined, and the nodal groups are indicated. The additional
margin required for including the distal lateral external iliac
nodes is shown in blue. The parametrium and the upper
vagina are shown in red, and the inguinal, pre-sacral and
lower para-aortic nodal regions are also indicated.
comprises the primary tumour, or tumour bed, structures at
risk of direct tumour spread, such as the parametrium, and
the draining lymph node regions. The pelvic lymph nodes,
however, are difficult to delineate as most cannot be
visualised on computed tomography or MRI, but still may
contain metastases. Because of greater conformity in all
dimensions, consistent and accurate target volume definition is particularly important with IMRT, as salvage
treatment for relapsed disease due to a geographical miss
is rarely successful [11].
With the complexity of dose pattern that can be achieved
with IMRT, it is now possible to select which nodal groups
need to be covered depending on tumour site and stage. The
proposed guidelines have been applied to generate an atlas
of reference images defining each of the pelvic lymph node
regions and enabling standardisation of the target volumes
for IMRT. It must be emphasised that there are no
pathologically enlarged nodes on these images, and it is still
important to ensure that all visible nodes are fully encompassed by the CTV, as nodes with a diameter greater than
8 mm are readily identified with computed tomography.
For gynaecological cancers, the nodal CTV would
typically include the external iliac, internal iliac and
obturator nodes. Treatment of the common iliac region is
indicated for tumours involving the cervix, or when there is
lymphadenopathy in another pelvic region [12e15]. The
distal lateral external iliac nodes often lie distant from the
vessels, and studies have shown that despite being missed
by conventional fields in 34e45% of cases, this region is
a rare site of recurrence [16e18]. Therefore, these nodes
do not need to be routinely encompassed and our practice
would be to include them only if there is other external
iliac nodal involvement, or if the target volume also
includes the inguinal regions. The lower pre-sacral nodes
are also included if there is tumour extension along the
uterosacral ligaments or if there is rectal involvement.
Although the images show the CTV for gynaecological
cancer, it would not be unreasonable to extrapolate the
results to male pelvic anatomy, and to use a similar target
volume when treating pelvic nodes for urological cancer.
The selection of the appropriate nodal groups depends
on existing data from surgical and autopsy series, but there
will increasingly be more information available from
functional imaging and from sentinel lymph node studies,
which could help to refine or individualise the target
volume. It will also be essential to collect data prospectively on the sites of pelvic recurrence in all patients
treated with pelvic IMRT to assess whether future modification of the target volume is necessary.
Acknowledgements. This research was supported by the XAppeal fund, Royal College of Radiologists and the BUPA Foundation, UK.
Discussion
Conformal radiotherapy is increasingly recognised as
offering benefit in normal tissue sparing in whole pelvic
irradiation. IMRT offers even greater potential for normal
tissue protection and dose escalation. The CTV usually
Author for correspondence: A. Taylor, Department of
Radiotherapy, Hammersmith Hospital, Du Cane Road, London W12
0HS, UK. Tel: þ44-20-8383-8132; E-mail: [email protected]
Received 6 April 2007; accepted 2 May 2007
Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002
ARTICLE IN PRESS
PELVIC LYMPH NODE ATLAS
3
Fig. 1 e The typical clinical target volume (CTV) for adjuvant pelvic radiotherapy in gynaecological cancer contoured in yellow, and
modifications shown to include lateral external iliac nodes (blue), inguino-femoral nodes (green) and the parametria and upper vagina (red).
The nodal regions indicated are para-aortic (PA), common iliac (CI), pre-sacral (PS), internal iliac (II), obturator (Obt), lateral (EIl), medial
(EIm) and anterior (EIa) external iliac, parametrial and paravaginal (Pm), and inguino-femoral (Ing) lymph nodes.
Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002
ARTICLE IN PRESS
4
CLINICAL ONCOLOGY
Fig. 1 (Continued)
Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002
ARTICLE IN PRESS
PELVIC LYMPH NODE ATLAS
5
Fig. 1 (Continued)
Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002
ARTICLE IN PRESS
6
CLINICAL ONCOLOGY
Fig. 1 (Continued)
Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002
ARTICLE IN PRESS
PELVIC LYMPH NODE ATLAS
7
Fig. 1 (Continued)
Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002
ARTICLE IN PRESS
8
CLINICAL ONCOLOGY
Fig. 1 (Continued)
Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002
ARTICLE IN PRESS
PELVIC LYMPH NODE ATLAS
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Please cite this article in press as: Taylor A et al., An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition,
Clin Oncol (2007), doi:10.1016/j.clon.2007.05.002