Recommendations from Gynaecological (GYN) GEC-ESTRO Working Group: Considerations and pitfalls in commissioning and applicator reconstruction in 3D image-based treatment planning of cervix cancer brachytherapy

Hellebust, Taran Paulsen; Kirisits, Christian; Berger, Daniel; Pérez-Calatayud, José; De Brabandere, Marisol; De Leeuw, Astrid; Dumas, Isabelle; Hudej, Robert; Lowe, Gerry; Wills, Rachel; Tanderup, Kari

doi:10.1016/j.radonc.2010.06.004

« Previous Next »Radiotherapy & Oncology
Volume 96, Issue 2 , Pages 153-160, August 2010

Recommendations from Gynaecological (GYN) GEC-ESTRO Working Group: Considerations and pitfalls in commissioning and applicator reconstruction in 3D image-based treatment planning of cervix cancer brachytherapy

Taran Paulsen Hellebust
- Department of Medical Physics, Oslo University Hospital, Norway
- Corresponding author. Address: Department of Medical Physics, Division of Cancer and Surgery, Oslo University Hospital, Oslo, Norway.
Christian Kirisits
- Department of Radiotherapy and Radiobiology, Medical University of Vienna, Austria
Daniel Berger
- Department of Radiotherapy and Radiobiology, Medical University of Vienna, Austria
José Pérez-Calatayud
- La Fe University Hospital, Valencia, Spain
Marisol De Brabandere
- Department of Radiotherapy, University Hospital Gasthuisberg, Leuven, Belgium
Astrid De Leeuw
- University Medical Centre Utrecht, The Netherlands
Isabelle Dumas
- Department of Radiotherapy, Institut Gustav Roussy, Villejuif, France
Robert Hudej
- Department of Radiotherapy, Institute of Oncology Ljubljana, Slovenia
Gerry Lowe
- Mount Vernon Cancer Center, Northwood, UK
Rachel Wills
- Mount Vernon Cancer Center, Northwood, UK
Kari Tanderup
- Department of Oncology, Aarhus University Hospital, Denmark

Received 21 April 2010; received in revised form 7 June 2010; accepted 8 June 2010. published online 21 July 2010.

Abstract

Image-guided brachytherapy in cervical cancer is increasingly replacing X-ray based dose planning. In image-guided brachytherapy the geometry of the applicator is extracted from the patient 3D images and introduced into the treatment planning system; a process referred to as applicator reconstruction. Due to the steep brachytherapy dose gradients, reconstruction errors can lead to major dose deviations in target and organs at risk. Appropriate applicator commissioning and reconstruction methods must be implemented in order to minimise uncertainties and to avoid accidental errors.

Applicator commissioning verifies the location of source positions in relation to the applicator by using auto-radiography and imaging. Sectional imaging can be utilised in the process, with CT imaging being the optimal modality. The results from the commissioning process can be stored as library applicators. The importance of proper commissioning is underlined by the fact that errors in library files result in systematic errors for clinical treatment plans.

While the source channel is well visualised in CT images, applicator reconstruction is more challenging when using MR images. Availability of commercial dummy sources for MRI is limited, and image artifacts may occur with titanium applicators. The choice of MR sequence is essential for optimal visualisation of the applicator. Para-transverse imaging (oriented according to the applicator) with small slice thickness (⩽5mm) is recommended or alternatively 3D MR sequences with isotropic voxel sizes. Preferably, contouring and reconstruction should be performed in the same image series in order to avoid fusion uncertainties.

Clear and correct strategies for the applicator reconstruction will ensure that reconstruction uncertainties have limited impact on the delivered dose. Under well-controlled circumstances the reconstruction uncertainties are in general smaller than other brachytherapy uncertainties such as contouring and organ movement.

Keywords: 3D brachytherapy, Applicator reconstruction, Commissioning