Supine MRI-guided navigation for tumor localization in breast cancer patients: a feasibility study.

A typical treatment for women with breast cancer is breast-conserving surgery
(BCS) followed by radiotherapy (RT), providing good survival rates. In order to
remove all tumor tissue during BCS, adequate tumor localization is essential.
Current localization procedures typically use a marker that is implanted in the
center of the tumor under ultrasonography (US) or stereotactic mammography (XM)
guidance. However, for patients with non-palpable or diffuse breast cancer it
would be beneficial to not implant one marker in the center, but multiple
markers at the borders of the tumor. Currently, tumor marker implantation is
prepared by assessment of prior-obtained imaging data, usually a combination of
mammography, ultrasound and contrast-enhanced MRI (CE-MRI). However, all
imaging data are acquired with the patient in another position than during the
marker implantation procedure and BCS when the patient is lying in supine
position. Secondly, tumor location and extent as seen on the imaging data is
not translated to the patients* anatomy of that day during implantation or
surgery.

Recently, supine breast MRI with an image quality comparable to diagnostic
prone CE-MRI has become available in our hospital. Firstly, supine MRI images
the breast in the identical patient setup as during marker implantation and
BCS. Secondly, a navigation system can be used to link the pre-obtained supine
MRI to the patient position during the implantation procedure and BCS. Such a
system is capable of visualizing the tumor as seen on the supine MRI with
respect to the patients* anatomy of that day. This is the first feasibility
study to assess the accuracy of marker implantation based on supine MRI and by
using such a navigation system.

Primary goal:
to assess the accuracy of a supine magnetic resonance imaging (MRI)-guided
electromagnetic navigation system used for tumor marker implantation in breast
cancer patients.

Secondary goal:
to assess the variability in target volume delineations on pre-operative CT and
registered CT-supine MRI between different radiation oncologists.

Informed consent will be obtained during the outpatient clinic appointment. On
the same day as the scheduled tumor marker implantation, a contrast-enhanced
MRI in supine position is acquired. Before acquisition of the MRI, five
reference markers are placed on the skin of the affected breast. Locations of
these markers is drawn on the skin of the patient using a permanent marker. The
reference markers will be visible on the supine MRI. Afterwards, tumor
delineation and the desired target point of the tumor marker is determined on
the supine MRI by the researcher and the radiologist.

Before the implantation procedure starts, the supine MRI with the corresponding
tumor delineation and marker target point is loaded into the navigation
software. An electromagnetic (EM) field generator (Aurora) is placed near the
table where the marker implantation will occur. Subsequently, the generator is
switched on in order to generate an EM field in the proximity of the patient
table. An electromagnetic (EM) reference sensor is attached to the implantation
needle in order to track the needle in the presence of the EM-field. After the
patient is positioned on the table, a point registration is performed using the
tracked needle between the reference markers on the supine MRI and on the
corresponding location of the markers on the skin of the patient.

During the marker implantation, the tracked needle is visualized with respect
to the tumor delineation and the corresponding target point on the supine MRI
by the navigation software. Before the needle is inserted into the breast, the
correct anatomical location is confirmed by ultrasonography (US). The correct
target point inside the breast is also verified with US before release of the
marker in the tumor.

After the implantation procedure, a mammography is performed according to
standard clinical practice. Additionally, a CT without contrast is acquired.

On the day of the marker implantation, a supine contrast-enhanced (CE) MRI is
acquired.
After the implantation procedure, a CT without contrast agent is acquired.

The additional burden for the patient consists of a supine MRI with
administration of contrast agent (gadolinium). The risks for an allergic
reaction are small since only patients will be included that underwent a
contrast-enhanced MRI in prone position before. Furthermore, a CT without
contrast agent will be acquired. The radiation load of this scan is negligible
since these patients will all undergo post-operative radiation. We estimate
that the image-guided navigated marker implantation will take 15 minutes longer
than the conventional marker implantation procedure.


Furthermore, the first 5 patients will undergo marker implantation accordingly
current clinical practice (using ultrasound-guidance). However, the
implantation procedure is prepared accordingly the new workflow including
acquisition of the supine MRI, tumor delineation and determination of target
point, registration of the supine MRI with physical space etc. In this manner,
the radiologist can get familiar with the new workflow and the viewing station
without the risk of delaying the procedure in the first included patients.