Clinical Trial Scan Schedule: What to Ask

Outside a trial, a scan is ordered when your doctor wants to know something. Inside a trial, scans sit on a calendar set before you enrolled. Their main job is to produce a number.

That number feeds the trial's endpoint: the result the study uses to judge the treatment. Two common endpoints depend entirely on imaging. The U.S. Food and Drug Administration (FDA) defines objective response rate as "the proportion of patients with tumor size reduction of a predefined amount and for a minimum time period." It defines progression-free survival as "the time from randomization until objective tumor progression or death, whichever occurs first."

So the date of your scan is itself data. That explains most of the rules below.

Before your first dose, the team does a baseline scan. It picks out the tumors it will follow and records their measurements. Every later scan is compared against that starting point.

FDA requires those rules to be fixed in advance: response criteria must be "predefined in the protocol before the start of the study."

Two questions follow. How many days before the first dose must the baseline scan happen? And will a scan from another hospital count, or must it be repeated? Repeats are common, and they are one reason screening takes longer than people expect.

Most solid tumor trials measure response using RECIST, short for Response Evaluation Criteria in Solid Tumors. FDA describes it plainly as "a standard way to measure how well a patient responds to treatment. It is based on whether tumors shrink, stay the same, get bigger, or spread to a new part of the body."

FDA notes that "a variety of response criteria have been considered appropriate (e.g., revised RECIST guideline (version 1.1))."

Cut-offs differ between versions and protocols, so ask directly: what percentage change counts as a response here, and what counts as progression? Also ask what happens if a new spot appears while the measured tumors shrink. That answer decides whether you stay on treatment.

Feeling well does not earn a postponed scan. Feeling poorly does not automatically earn an early one.

The reason is measurement bias. FDA warns that "bias can be introduced if the frequency of long-term follow-up visits is dissimilar between the study arms," and instructs that "visits and radiological assessments, when applicable, should be symmetric between the two study arms to prevent systematic bias."

Put simply: if one group were scanned more often, its cancers would appear to grow sooner, purely because someone was looking. Same schedule, fair comparison.

Protocols usually allow a window of a few days around each scan date. Ask how wide yours is, and whether a missed scan can take you off the study.

FDA advises that "when the primary study endpoint is based on tumor measurements (e.g., PFS or ORR), tumor assessments generally should be verified by central reviewers blinded to study treatments." A blinded reviewer does not know which treatment you received, which stops expectation from shading the measurement.

The site radiologist and the central reviewer do not always agree. Ask which reading decides whether you continue treatment, and how fast your own doctor gets it. Central review can lag by weeks.

Repeat scans mean repeat radiation. That is fair to ask about.

For scale, the National Cancer Institute (NCI) reports that the average person in the United States receives "an estimated effective dose of about 3 millisieverts (mSv) per year from naturally occurring radioactive materials." Against that baseline:

• A low-dose lung CT is about 1.5 mSv, which NCI equates to "6 months of natural background radiation."
• A typical chest CT is about 6.1 mSv, roughly "2 years of natural background radiation."
• A whole-body CT is "about 10 to 20 mSv, or more than three times the estimated average annual dose."
• FDA lists a typical abdominal CT at 8 mSv.

FDA puts the risk this way: a 10 mSv CT scan "may be associated with an increase in the possibility of fatal cancer of approximately 1 chance in 2000," against a natural lifetime risk of "about 1 chance in 5 (equal to 400 chances in 2000)." NCI's position is that for someone with signs or symptoms of disease, the benefits of a CT scan "greatly outweigh any potential health risks."

Two useful moves. Ask whether any scheduled CT could be an MRI instead, since MRI uses no ionizing radiation. And, as NCI notes, some organizations recommend that people keep "a record of the imaging examinations they have received."

Many trial scans use a contrast agent, a dye that makes tissues easier to tell apart.

NCI notes serious reactions are "very rare." Mild ones include "mild itching or hives." Severe reactions can involve "shortness of breath and swelling of the throat." NCI also warns that "the contrast agents used in CT can cause kidney problems for certain patients."

So ask whether kidney function is checked before each contrast scan, what to do if you have reacted before, and whether the protocol allows a scan without contrast if your kidney numbers slip.

FDA notes that response rate "may not always correlate with survival," and that progression-free survival is "potentially subject to assessment bias, particularly in open-label studies." Overall survival, the time from randomization until death from any cause, is what FDA calls "the most reliable cancer endpoint."

None of that makes a shrinking tumor meaningless. It does mean a good scan is one measurement at one moment, not a promise.

Scans split the way other trial costs do. Imaging you would have had anyway is a routine patient care cost. Imaging done only because the study needs the data is a research cost.

Medicare's trial coverage rule is explicit that it does not pay for "items and services provided solely to satisfy data collection and analysis needs and that are not used in the direct clinical management." Sponsors typically cover those.

Get it in writing: which scans go to insurance, which go to the sponsor, and who to call if a bill arrives.

• On what weeks are scans due, and how wide is the window around each date?
• What change on a scan would take me off this treatment?
• If I feel worse between scans, can we scan early, and does that break protocol?
• Who reads the scan first, and when will I hear the result?
• Is a central blinded review involved, and which reading guides my care?

• U.S. Food and Drug Administration — Clinical Trial Endpoints for the Approval of Cancer Drugs and Biologics.
• U.S. Food and Drug Administration — Patient-Friendly Language for Cancer Clinical Trials.
• National Cancer Institute — Computed Tomography (CT) Scans and Cancer Fact Sheet.
• U.S. Food and Drug Administration — What are the Radiation Risks from CT?.
• Centers for Medicare & Medicaid Services — NCD 310.1, Routine Costs in Clinical Trials.

Helpful next pages include What Does RECIST Mean in Cancer?, What Does Measurable Disease Mean?, What Are Endpoints in a Clinical Trial?, Reporting Side Effects in a Clinical Trial, Waiting for Cancer Test Results: How to Cope, Clinical Trial Screening Visit: What to Expect.