Routine Use of Positive Oral Contrast Material Is Not Required for Oncology Patients Undergoing Follow-up Multidetector CT

ByDr. Naglaa Mahmoud

Registrar of Clinical RadiologyKCCC

Introduction

Historically, the length and convoluted course of the small bowel has presented diagnostic challenges for abdominal CT in differentiating between bowel and pathologic abnormalities.

Opacification of the bowel with positive oral contrast material has therefore been recommended for the correct interpretation of abdominal CT scans.

Current guidelines for performing abdominal oncology CT also include recommendation for the use of positive oral

contrast material, and the internationally recognized Response Evaluation Criteria in Solid Tumors, or

RECIST, recommends the use of positive oral contrast material in all patients undergoing abdominal CT in

therapeutic trials.

• The use of positive oral contrast material is associated with a number of problems.

• It is time-consuming because patients generally need to arrive early for their appointment.

• Drinking a large quantity of liquid prior to scanning.

• Further, the gastrointestinal tract is not always consistently adequately opacified with oral contrast material, which can be due to several factors such as poor tolerance of oral contrast material by patients or due to variable gastrointestinal tract motility.

• This can cause difficulty in interpretation and pseudotumor effects.

There is also increasing evidence that positive oral contrast material is not required in adult trauma and negative oral contrast material

may be preferred in pediatric or adult imaging.

Much of the evidence for positive oral contrast material dates from the era of single-section CT, with long 4–6-second scan rotation

times and thick (10-mm) collimation resulting in considerable bowel peristaltic motion during section acquisition.

With the advent of multidetector CT, we are now able to obtain image data with thinner collimation and shorter scan times, down to

0.33 second, which reduces the amount of bowel motion possible during section acquisition.

This also allows greater anatomic coverage in a shorter time, improving intravenous contrast enhancement.

This improved spatial and temporal resolution allows better assessment of the mesentery, bowel wall enhancement, and

vasculature and improves differentiation between bowel loops and pathologic findings.

The purpose of this retrospective medical audit was to evaluate the effect of discontinuing routine administration of oral contrast material to oncology patients undergoing follow-up multidetector CT on reader evaluation of study adequacy.

Materials and Methods

I.Analysis of 100 patients’ experience of CT.

II.Abandoning the routine use of positive oral contrast material for follow-up scans in general oncology patients undergoing multidetector CT scan was audited for 447 patients and included 5–13-month follow-up.

The patient satisfaction study and clinical audit were performed according to local institutional audit guidelines.

Since this was a clinical audit project, ethical approval was not required under UK National Health Service research governance arrangements.

I. Patient Satisfaction Survey

From October 2, 2006, patients undergoing abdominal multidetector CT for oncology indications with protocols for positive oral and intravenous contrast material were asked to fill out a patient satisfaction questionnaire after their scan.

Recruitment continued until 100 completed forms were available.

The standard contrast material was barium sulfate suspension (4.9% wt/vol in 225 mL, E-Z-CAT; E-Z-Em, Lake Success, NY) diluted in 1000 mL of water, making a suspension of 1.1% wt/vol.

Patients were asked to avoid solid food for 3 hours prior to appointment.

Forty minutes prior to the scan, they were given the 1-L suspension and asked to drink it slowly and continuously until their scan time.

The patients graded their experience for the following: information provided about receiving scan appointment, waiting time from referral to appointment, staff attitude during their visit, the experience of the oral contrast material used, intravenous cannulation and contrast material injection, and overall experience.

Patients were asked to score their experience on a 10-cm visual analogue scale marked from bad to excellent.

The score was taken as 0 being the worst and a score of 10 being the best.

Patients were also asked to state the worst thing about their scan experience.

II. Patient Audit

The audit period included a 6-month period from December 2006 to May 2007 and then a further 7 months to cover follow-up data.

For oncology patients undergoing follow-up CT with a multidetector scanner the protocols were changed to abandon the use of positive oral contrast material.

Solid food was avoided for 3 hours prior to appointment, but fluids were not restricted.

All scans were obtained with a 16-section CT scanner.

Images were acquired with section reconstruction was at 2.5-mm thickness.

Intravenous contrast material was used unless contraindicated by previous reaction, impaired renal function, or difficulty in obtaining venous access.

Standard protocol for abdomino-pelvic scans is normally 100 mL of iomeprol (350 mg of iodine per milliliter) injected with a power injector at 3 mL/sec with a scan delay of 70 seconds.

The review of images was performed in two stages:

The first stage was performed prospectively to immediately identify if patients needed to be recalled for oral contrast material and whether the abandonment of the routine use of contrast material was a clinically safe decision.

All scans were reported by one of four radiologists specializing in oncology and cross sectional imaging, who had 15, 10 , and 6 years of experience in radiology.

All scans were reported with reference to any previous scans.

Scans were reviewed to determine the ability to delineate the bowel and to assess whether any abnormality could be identified and defined within the peritoneum and the surrounding structures.

The results were recorded as follows:

Category 1 bowel clearly identified, no need for positive oral contrast material;

Category 2 bowel clearly identified, identification assisted by reviewing the previous scan;

Category 3 segments of bowel not clearly identified, but patient not recalled as positive oral contrast material is unlikely to change the report in a clinically important manner; and

Category 4 segments of bowel not clearly identified, case requires recall for oral contrast material.

For the second stage of the review, all scans in categories 2–4 were reviewed retrospectively and independently 7 months after the end of the study (November 2007) by the same four authors.

Scans were reclassified to:

Category 1 only if all the reviewers independently were clinically confident that the lack of positive oral contrast material did not have any deleterious effect on the scan quality.

Category 2 or 3, if bowel clarity was no better on the initial scan in which positive oral contrast material were used.

The results were statistically analyzed.

Results

I. Patient Satisfaction Survey

One hundred patients completed the questionnaire.

The satisfaction survey showed that patients found oral contrast material to be the least pleasant experience (mean score, 4.87; 95% confidence interval: 4.27, 5.47) and the second worse was cannulation and intravenous injection (mean score, 6.72; 95% confidence interval: 6.14, 7.3); the other categories were similar.

II. Patient Audit

A total of 447 patients undergoing follow-up multidetector CT were included in the audit period. Of these, 285 (64%) underwent further follow-up imaging.

Mean age was 61 years (range, 20–94 years), with 209 male (mean age, 59 years; range, 25–87 years) and 238 female (mean age, 62 years; range, 20–94 years) patients.

No patient was recalled for positive oral contrast material.

During the audit period, including 7-month follow-up, no case has been reported where a diagnostic error had been made that could be attributed to a lack of positive oral contrast material.

The Table shows the range of oncology indications for follow-up scans, use of intravenous contrast material, and the percentage of patients with peritoneal disease and retroperitoneal lymphadenopathy for cases with good and poor bowel visualization.

In the initial review, the bowel could be adequately identified and differentiated from disease in the absence of oral contrast material in 403 (90.2%) of 447 patients.

285 of 447 (64%) patients had follow-up scans, with no scans showing missed disease.

Initial classification was category 2 in 14 cases and category 3 in 30 cases, therefore difficulty in defining the bowel was recorded in 44 of 447 cases (9.8%).

This group included a higher proportion of patients with peritoneal disease (22 of 44, 50%) and in patients with ovarian and abdominal sarcoma diseases.

Seven months after the end of the study period, the second-stage review was performed.

Each individual reviewer independently re-categorized 32–36 of the 44 scans, originally recorded as category 2 and 3, as category 1 “bowel could be adequately identified”.

Agreement in the assessment was only fair, and only 21 of the 44 scans were independently re-categorized as “bowel could be adequately identified” by all 4 reviewers.

Therefore, in the second-stage review, it was believed that the bowel could be adequately identified and differentiated from disease in the absence of positive oral contrast material in 424 of 447 scans (94.9%).

The remaining 23 of 447 scans originally classified as 2 or 3 (5.2%) were also primarily noted in patients with peritoneal disease or with lack of intravenous contrast material.

16 of these 23 (70.0%) patients had follow-up scans; in no case was there a missed disease.

7 of 447 scans (1.6%) were classified as “bowel not clearly identified” and no follow-up CT was performed.

Discussion

Findings of the study show that positive oral contrast material is for most oncology patients the worst aspect of their CT experience.

In a series of 447 patients undergoing follow-up CT for oncology indications there is no clinically identifiable loss in diagnostic performance if positive oral contrast material is not used. This is confirmed by the cases with further follow-up CT, which showed no missed disease, even in cases where bowel was not clearly defined. In this study, difficulties were encountered with thin patients, peritoneal disease close to bowel loops, and in patients examined without the use of intravenous contrast material.

Oral contrast material may be justified in some of these situations, although it is not routinely use oral contrast in any of these groups.

During the study, it was also found that the positive oral contrast material may mask certain findings such as subtle mucosal deposits seen in carcinoid or melanoma and calcified peritoneal deposits.

There are collateral benefits of not using positive oral contrast material.

In addition to the benefit of not having to drink up to a liter of fluid prior to the scan,

The length of appointments is reduced, as patients arrive 10 minutes rather than 60 minutes prior to their appointment time.

The cost per patient of a positive oral contrast material is not high ($4–$10 per patient). However, this can amount to over $15 000 per year for a single scanner dedicated to oncology.

Limitations of the study

There was no comparison of reading time, although the authors do not feel that the absence of oral contrast material substantially changes the reporting time.

The impact of patient size on study adequacy was not formally measured, and the amount of abdominal fat may affect bowel visualization.

Only one contrast medium was used for this study, and it is possible that other media may be better tolerated.

The reason of poor tolerance of oral contrast agents was not specifically tested in this group, although it is believed that it is related to both generic problem of drinking a large volume of liquid with suboptimal flavor and the presence of cancer.

Conclusion

Authors suggest that if multidetector CT is available, positive oral contrast material should not be a routine requirement for follow-up abdomino-pelvic scans in oncology patients.

The requirement for routine positive oral contrast material should also be removed from research protocols (such as RECIST protocols) in these patients unless there is a specific indication for their use, such as known peritoneal disease or stage 3 ovarian tumors.

This recommendation should not preclude using positive oral contrast material in certain situations, such as in patients who are very thin or are unable to have intravenous contrast material.

Thank you