International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationConformal Brachytherapy Planning for Cervical Cancer Using Transabdominal Ultrasound
Introduction
Brachytherapy has proven efficacy in treating cancer of the cervix (1). Its effectiveness rests on the technical quality of the implant 2, 3. Yet, most cervix brachytherapy is applied without image guidance and only planned with the aid of two-dimensional (2D) X-ray imaging. Computed tomography (CT) is slowly replacing traditional simulators, but often the pear-shaped distribution based on applicator size and standard loadings continues to be used to cover the paracervical triangle 4, 5, 6.
The introduction of image-based planning for brachytherapy has raised questions about the volume and nature of the tissues incorporated into the brachytherapy field. Definition of a target is a new concept in cervix brachytherapy being investigated by the Groupe European de Curietherapie and the European Society for Therapeutic Radiology and Oncology (GEC-ESTRO) group through an international study. The volumes of normal tissue within the radiation field become apparent on imaging and may shed some light on historical toxicity rates and late complications.
Although residual tumor volumes cannot always easily determined by CT or ultrasound (US), these modalities can be used to verify the position of the tandem in the uterus, and to assess dose to surrounding normal structures. Radiotherapy centers are slowly adapting these imaging modalities.
Transabdominal US has been used to assist applicator placement in this institution since 1985. Magnetic resonance imaging (MRI) was introduced in 2001 to assess tumor response to external beam treatment. The next logical step was to assess brachytherapy dosimetry on the MRI scan and develop an image-based planning and treatment protocol. Over time a strong correlation between the size and shape of the uterus and cervix, containing residual tumor, as seen on the US and MRI images, was observed (Fig. 1). It became apparent that US could give an accurate depiction of the applicator within the cervix and uterus, and the cervix and uterus within the pelvis. US was progressively incorporated into the protocol to avoid uterine perforation and to assist with the dosimetric coverage of the cervix, residual tumor, and uterus (7).
This retrospective study aimed to validate conformal US-based planning. In the period under review, 2D planning was the norm. Infrastructure and facilities did not support three-dimensional (3D) planning. In an effort to improve on standard dosimetry-based on 2D X-rays, an imaging modality was sought that could provide sufficient anatomical information to help define a target and ensure target coverage and sparing of surrounding normal tissues. The primary aim was to compare isodose distributions resulting from high-dose-rate (HDR) standard (STD) plans, US-derived plans, and 2D MRI derived plans with the final dosimetry achieved based on the combination of planning methods used in treating patients.
Section snippets
Materials and Methods
This was a retrospective comparative study of 71 patient's treatment plans. This study was approved by the Peter MacCallum Cancer Centre Ethics committee. All patients were newly diagnosed with locally advanced cervix cancer, had pretreatment MRI available, and received chemoradiation and brachytherapy with curative intent between October 2002 and July 2005.
Results
Data of 71 patients were examined in this study. The characteristics of the patients are described in Table 1. The median age of patients was 58 years. The pretreatment tumor volumes were 56 mL (mean), 44 mL (median), with a range of 2–270 mL. Residual tumor volumes at first brachytherapy insertion as assessed on MRI were 15.7 mL (mean), 11.7 mL (median), with range of 0–107 mL.
Discussion
This study suggests that using US imaging in cervix brachytherapy can substantially reduce doses to organs at risk while not compromising dose to the target volume.
Incorporation of soft-tissue imaging into gynecological brachytherapy programs has been developing for many years. Confirmation of the spatial accuracy of anatomy and applicator reconstruction, improved organ visualization, more accurate assessment of dose to organs, and the merits and disadvantages of each modality are well
Conclusion
This study suggests that important improvements can be made to current treatments based on standardized 2D X-ray image-based planning. It has been shown that US can identify an effective target volume. By using 2D US, it is possible to improve technical accuracy, visualize organ boundaries, and, with experience, plan conformal treatments that by definition spare organs at risk. US is easily accessible, portable, and inexpensive. Use of US allows for delivery of safe treatment in a simple
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Cited by (66)
A novel ultrasound probe calibration method for multimodal image guidance of needle placement in cervical cancer brachytherapy
2022, Physica MedicaCitation Excerpt :During the insertion of interstitial needle, real-time MRI guidance can ensure that the tumor can be punctured accurately and reduce the possibility of inadvertently inserting the needle into adjacent structures [16,17]. However, in most radiotherapy centers, MRI guidance requires moving patients from the brachytherapy suite or operating room to the imaging department, which may cause the applicator to move within the target area [11]. To solve the above problems and improve the accuracy of needle placement, an approach to register US images and the real-time rendering model of interstitial needle in preoperative MRI images is proposed in our previous study [18].
Applicator for cervical brachytherapy for MRI or CT guided therapy
2021, Technical Innovations and Patient Support in Radiation OncologyGEC-ESTRO/ACROP recommendations for quality assurance of ultrasound imaging in brachytherapy
2020, Radiotherapy and OncologyA fast method for simulating ultrasound image from patient-specific CT data
2019, Biomedical Signal Processing and Control
Conflict of interest: none.