An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition

doi:10.1016/j.clon.2007.05.002

Clinical Oncology

Volume 19, Issue 7, September 2007, Pages 542-550

https://doi.org/10.1016/j.clon.2007.05.002 Get rights and content

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.

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 1, 2, 3. 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 40–70% 4, 5, 6. 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 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 >99% 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.

Section snippets

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

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.

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 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

Acknowledgements

This research was supported by the X-Appeal fund, Royal College of Radiologists and the BUPA Foundation, UK.

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Original articleAn Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition

Abstract

Aims

Materials and methods

Results

Conclusion

Introduction

Section snippets

Materials and Methods

Results

Discussion

Acknowledgements

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Gynecol Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Gynecol Oncol

Gynecol Oncol

Cancer Lett

Original article
An Atlas of the Pelvic Lymph Node Regions to Aid Radiotherapy Target Volume Definition