The comparison of the diagnostic yield of low dose abdominal CT versus normal dose abdominal CT in bariatric patients with abdominal pain

The number of bariatric surgeries performed is increasing due to the growing
incidence of obesity in the general population. Bariatric surgery (BS) has many
benefits, including weight loss, and proven reduction of comorbidities such as
hypertension, diabetes, hyperlipidemia, obstructive sleep apnea, joint
complaints and gastroesophageal reflux disease. However, research has shown
that 33% of patients experience (chronic) abdominal pain after BS. This leads
to frequent visits of BS patients to the emergency room and outpatient clinic.
During these visits, extensive diagnostic testing is often required to
determine the cause. The most commonly used tests in this case is the abdominal
CT scan. In our own research at the Spaarne Gasthuis on the patient population
presenting with abdominal pain complaints after BS, we found that 66% of
patients undergo at least one abdominal CT scan (data not yet published).
Moreover, some patients even receive up to six CT scans in a single year.
Recurrent CT scans may impose a health risk in this population due to the link
between radiation exposure and increased risk for malignancy (1, 2). Especially
abdominal and pelvis CT scans account for 50% of the collective CT dose (3). In
addition, in our own recent study, we saw that 90 percent of patients with
abdominal pain complaints were female with an average age of 47.2 years This
means that a substantial part of CT receiving patients were females still in a
fertile period of their lives. Recurring radiation exposure may be especially
harmful in this group.

A normal abdominal CT scan gives a radiation exposure of 5.76 * 3.22 mSv
(range: 1.13-12.71) in females and 4.37 * 1.66 mSv (range: 1.36-8.07) in males
(4). There is, however also a low dose abdominal CT available. A low dose
abdominal CT scan reduces this radiation load to <2.5 mSv, which is comparable
to two abdominal X-rays. Previous studies have shown that a low dose CT-scan
can be used in the assessment of acute non-traumatic abdominal pain in patients
without prior bariatric surgery (5, 6). In these studies, conditions were
diagnosed that were mainly related to the following organs: the large bowel,
the small bowel, biliary tracts, pancreas, kidney or bladder, pelvic
collections, abdominal wall, liver and chest. The accuracies of the radiologist
in this study were respectively 99% and 100%. Low dose CT scans were
especially reliable in patients with a body mass index (BMI) <30 kg/m2. The
population for the proposed study is post-BS and often falls into this category.

Abdominal pain in BS patients may be caused by acute life-threatening diagnoses
such as internal herniation. Reduction in the number of CT scans performed in
BS patients is hard to achieve as the only alternative to CT is abdominal
surgery. Instead, effort to try to expose patients to lower dose of radiation
would be a good alternative to still be able to diagnose abdominal after BS
sufficiently.

Primary Objective:
• Compare the diagnostic performance of the low dose abdominal CT scan to the
normal dose abdominal CT scan in diagnosing causes of abdominal pain.

Secondary Objectives:
• Compare the diagnostic performance of diagnosing internal herniations on the
abdominal low dose CT scan to the normal abdominal CT scan.
• Compare perceived image quality between both CT scans
• Analyze the difference between radiation dose measurements expressed as DLP
and CTDIvol

This study is designed as a single-center observational case-control study and
will take place in the Spaarne Gasthuis location Hoofddorp. Cases are people
with a history of Roux-en-Y Gastric Bypass who present themselves at the
emergency room with complaints of abdominal pain and in whom an abdominal CT
scan is indicated to investigate the cause of these abdominal pain complaints.
Other bariatric surgeries are not included because only patients with a
Roux-en-Y gastric bypass are at risk of developing an internal herniation.
Patients will receive standard care through the indicated regular CT scan and
will be asked to receive an additional low dose CT scan. The data of the low
dose CT scan will be compared with the normal dose CT scans of the same
patients at a later time.

Participants will be recruited at the emergency department by the attending
physician from the surgery department or the emergency department. Patients
with abdominal pain after BS interested in participating in this study will
receive additional written information and an informed consent interview will
be conducted by one of the clinicians on call of the surgery department or the
emergency department. Due to the urgent care setting, informed consent forms
will be signed immediately after explanation of the informed consent. The
patient will then immediately receive a normal and a low dose CT scan.
Participation in this study should cause no delay in the normal diagnostic
process.
The normal dose CT scan will be used clinically in the diagnosis of the
abdominal pain via normal protocol. For the study both the normal dose and the
low dose CT scans will be reviewed at a later moment by two independent
abdominal radiologists and scored according to standardized protocol. During
the interim and final analysis, the assessments of both CT scans will be
compared and analyzed. The time between making the CT scan and the assessment
of the two independent radiologists will be three months. Subsequently, in the
case of a suspected internal herniation, the scan will also be compared with
the outcome of the diagnostic laparoscopy.

Study participation will end three months after making the normal dose and low
dose CT scan. This allows for a three months follow up. The duration of the
study will be until 120 patients are included. It is expected that this will be
achieved within six months.

Participants will receive an extra low dose CT scan on top of the already
planned normal dose CT scan for abdominal pain. The low dose CT scan imposes a
very low risk on radiation-induced cancer. There is no direct benefit for the
participants, but in the long term it may be that in the event of a recurrence
of abdominal pain they will receive less radiation exposure because they can
have a low dose CT scan instead of a normal dose CT scan due to the findings in
this study.