Feasibility of CT-guided percutaneous needle puncture for kidneys with CASone system

Nephrolithiasis has a prevalence of 5.5% in the general population and a peak
incidence between the age of 30-50 years. The life time risk of a renal stone
in the Western world is 10-15%.
According to EAU guidelines large renal calculi should be considered for
primary PCNL treatment. PCNL is more invasive than ureteroscopy with
subsequently higher complication rates including bleeding and sometimes blood
transfusions. Therefore, in PCNL the most important step to minimize
complications and achieve the highest success rate, is puncture of the calyx of
choice for optimal access to the kidney. Especially with multiple kidney stones
in different poles, entering of the kidney via the appropriate access may
enable the urologist to reach every angle of the kidney and achieve a high
stone-free rate. Despite this ideal scenario, multiple tracts may be needed for
complete stone removal. Obviously, this is not favorable to the patient and may
increase the risk for complications like bleeding and lead to a longer
convalescence time. The greatest challenge during surgery is to translate
preoperative 2D CT scan images to a real-life 3D approach of the kidney. It
frequently occurs that a different calyx is punctured from the initially
planned one, for instance a dorsally located instead of a ventrally located
calyx. This problem may be solved with 3D augmented reality or image-guided
navigation surgery. General shortcomings in image-guided surgery are the
anatomical changes of kidney position between preoperative imaging in supine
position and intraoperative lateral decubitus or prone position. Furthermore,
intraoperative kidney location may change by respiration movements. With
intraoperative CBCT scan imaging and image-guided navigation for kidney
puncture these shortcomings may be overcome.
The potential features of the CASone system have previously been shown in
reports for hepatocellular carcinoma. Stereotactic image-guided microwave
ablation (SMWA) is performed with CT-guidance with needle trajectory, ablation
planning and automatic single-marker patient registration. Needle placement and
ablation coverage was controlled by image fusion. SMWA is a safe and efficient
treatment for HCC offering a curative treatment approach in general and in
particular for lesions not detectable on conventional imaging or untreatable
due to difficult anatomic locations. The first reports about the CASone system
for kidney tumors have appeared (www.cascination.com), but no publications in
the field of kidney stone approach and treatment exist. As the CASone system is
a CT-based stereotactic navigation system we have to carefully evaluate its
merits but also the downsides like radiation exposure.

The aim of this study is to demonstrate the feasibility of CBCT-based
stereotactic navigation to perform a better and optimal renal access puncture,
which may enable higher stone free rates. This may lower intraoperative ERD
during PCNL with fluoroscopy and eventually will lead to less CT scans being
performed during follow-up. We expect the radiation doses of CBCT-based
navigation to be within the acceptable range for intraoperative imaging
procedures.

Prospective explorative study

Anticipated clinical benefits:
The CT-based stereotactic navigation system for precise positioning of the
needle during PCNL potentially improves the access to the kidney. Instead of a
2D ultrasound-guided or fluoroscopy based access to the kidney, this approach
enables us to perform an intraoperative 3D reconstruction of the kidney
position and image-guided navigation access of the needle into the kidney.
Ideally, this will lead to optimal kidney entrance without necessity for extra
needle punctures and subsequently to higher accuracy of stone removal and
stone-free rate. For this feasibility study the first step is to evaluate
whether access to the kidney with this navigation technique is possible and
safe. The CASone system measures the accuracy of needle position after puncture
with an intraoperative placement planning. Therefore, direct feedback on exact
needle tip position is provided.

Anticipated adverse events:
Potentially extra radiation dose is given to these patients with the
intraoperative CBCT round. Therefore, we evaluated the effective radiation
dosis (ERD) of the previous 20 patients who underwent an PCNL in our hospital.
The access to the renal collecting system has been performed with a combination
of ultrasound and fluoroscopy guidance. The mean ERD during the whole procedure
was 1.4 mSv, which is comparable to the literature (1-9mSv). For CBCT
stereotactic navigation an ERD of maximally 3.2 mSv per rotation is
anticipated, which is acceptable, please see enclosed Radiation Ethics Form for
further clarification.
Hypothetically, higher stone-free rate reduces the number of routine plain
radiography of the kidney (0.1-0.3 mSv) or a non-enhanced CT-scan (4.5 mSv)
during follow-up on the outpatient clinic. In the historical cohort, we
performed non contrast CT-scan in 11/20 patients, of which 6 had
re-interventions (including additional intraoperative radiation exposure) and 5
went into intensive follow-up with imaging because of residual stones. Routine
plain radiography of the kidney was performed in 17/20 patients. As more
accurate kidney access and therefore possibly improved stone removal might be
expected from CASone, our study patients may eventually receive lower ERDs than
patients who undergo routinely performed PCNL. Of course this will be measured
and is part of the follow-up and evaluation in this group.