Glossary

The payload is the poison an ADC carries, usually a chemotherapy far too toxic to give on its own.

Cancer spread to the bones, most common in prostate, breast, lung, kidney and thyroid cancer and myeloma. It causes pain, fractures and high calcium, and the complications are counted in trials as 'skeletal-related events'.

Anything an antibody or immune cell can recognise, typically a protein on a cell's surface. In cancer, an antigen is the flag that tells a drug or an immune cell 'this is the cell to attack'.

The soft tissue inside bones where all blood cells are made. Chemotherapy damages it, causing the low blood counts that limit how much treatment a patient can take.

The molecule that fits into a receptor and switches it on: growth factors, hormones and cytokines are all ligands. Cancers make their own ligands or mutate receptors so none is needed, and some drugs act on the ligand itself, as bevacizumab does by soaking up VEGF.

Regions of a tumour that have outgrown their blood supply and are short of oxygen. They resist radiotherapy and some chemotherapy, and drive the tumour to become more aggressive.

Neuroblastoma soaks up MIBG, a radioactive cousin of noradrenaline; the Curie and SIOPEN scores count how many body regions still light up on the scan, and a score that has not fallen enough after the first rounds of chemotherapy marks a child who is unlikely to be cured with the standard plan.

How fast PSA is rising matters more than its level: a doubling time under ten months after surgery or radiotherapy, or under nine months in castration-resistant disease, marks the men whose cancer is moving quickly and who benefit from earlier hormone therapy or a PSMA scan, while PSA density (PSA divided by prostate volume) helps decide who needs a biopsy at all.

Loss of the succinate dehydrogenase enzyme, shown by a negative SDHB stain, marks a small family of tumours (some stomach GISTs, paragangliomas and phaeochromocytomas, a rare kidney cancer) that are often inherited, occur in young people, ignore imatinib and grow slowly; the stain is the trigger for germline testing of the whole family.

A molecular 'cage' that grips a radioactive metal atom tightly so it stays attached to the drug all the way to the tumour, instead of leaking out and going to the wrong part of the body.

A way of describing how 'pure' a batch of radioactive material is: whether ordinary, non-radioactive atoms of the same element were deliberately or accidentally mixed in during manufacture.

A quality check on a radioactive drug that asks: of all the radioactivity in the vial, what fraction is actually in the correct, working chemical form, rather than stuck to the wrong molecule or floating free?

A radioactive drug can damage itself: the radiation it gives off breaks apart water and other molecules in the vial, creating reactive fragments that attack the drug molecule and reduce how much of it is still working correctly by the time it reaches the patient.

The time it takes for the amount of a drug in the blood to fall by half. It sets how often a drug must be given: hours to a day for small molecules such as kinase inhibitors, so they are taken daily, and two to four weeks for antibodies, so they are given every three or six weeks.

Using high-energy X-rays or particles to damage the DNA of cancer cells in a precisely aimed volume of the body. On its own it cures early prostate, larynx, cervix and skin cancers, it is combined with chemotherapy in head and neck, lung, oesophageal and rectal cancers, and about half of all cancer patients receive it.

PSA rising again after surgery or radiation, usually years before anything shows on a scan.

Cancer that has spread to only a few places, which may still be curable by treating each spot.

The standardised uptake value (SUV) is a number for how brightly a spot lights up on a PET scan.

A measure of how much radiation energy actually landed in a piece of tissue, not how radioactive the source was. It is what determines whether a tumour or an organ is actually being treated or harmed.

Deciding how much radioactive drug to give a patient. Most approved radioligand therapies today use the same fixed amount for everyone, but some clinics instead measure each patient's own radiation exposure and adjust the amount up or down to try to give more benefit with less harm.

A way of converting a physical radiation dose into a single number for comparing radiation risk across different types of radiation and different organs. It is used for radiation-protection purposes, not for prescribing cancer treatment doses.

The standard recipe physicists use to work out how much radiation dose a patient's organs and tumours actually received from an injected radioactive drug, based on how long it stayed in the body and where it went.

A number that says how much more (or less) biological damage a given amount of one type of radiation causes compared with the same physical amount of a reference radiation. Alpha particles are typically several times more damaging, gray for gray, than the beta particles used in more established radioligand therapies.

A graph of how much of an injected radioactive drug is present in an organ or tumour at different times after the injection. It shows the drug arriving, peaking and then clearing out, and it is the raw data that personalised radiation-dose calculations are built from.

PSA50 is the share of patients whose PSA falls by at least half on treatment, and PSA90 the share whose PSA falls by 90%.

A simple 1-to-5 score doctors use on a PET scan of lymphoma to say whether treatment is working, by comparing how bright the tumour looks against two normal reference areas: the blood in the chest and the liver.

Right after some cancer treatments start working, a scan can briefly look worse before it looks better, because healing bone or an early immune response makes lesions light up more, not because the cancer has actually grown. Doctors wait and repeat the scan before deciding treatment has failed.

A 0-to-4 scale doctors use to describe how strongly a tumour lights up on a somatostatin receptor scan, by comparing it with the normal liver and spleen. A higher score generally means the tumour is a good candidate for peptide receptor radionuclide therapy.

A standard 1-to-5 scale that nuclear medicine doctors use to describe how likely a spot seen on a PSMA PET scan is to be prostate cancer, so different hospitals describe the same finding the same way.

A simple number that says how much brighter a tumour looks on a scan compared with the normal tissue around it or nearby. A higher ratio makes a tumour easier to see and count.

How fast the tumour cells are dividing, measured by Ki-67 staining, separates slow-growing neuroendocrine tumours from aggressive neuroendocrine carcinomas and decides the treatment.

Radiation coming from deep inside the body has to pass through more tissue to reach the scanner's detectors than radiation from near the skin, so without correction, deep organs look falsely dim. Attenuation correction uses a separate scan (usually a CT) to fix this and make the image quantitatively accurate.

The two units used to state how radioactive something is. The becquerel (the modern, official unit) counts one radioactive decay per second; the curie (the older unit, still common in the United States) equals 37 billion decays per second.

The time it takes the body to clear out half of a substance through ordinary biological processes (metabolism and excretion), separate from any radioactive decay. A drug that the kidneys clear quickly has a short biological half-life regardless of which radioactive atom is attached to it.

Adjusting a radioactivity measurement to account for the fact that the sample kept decaying between the moment it was measured and the moment you actually care about, such as when the dose was drawn up versus when it was injected, or between two scans taken hours apart.

The real-world time it takes for the radioactivity in a patient's organ to fall by half, combining both the radioactive atom's own decay and the body's own clearance of the drug. It is always shorter than either process acting alone, and it is the number that actually drives how much radiation dose an organ receives.

A measure of how densely a particle of radiation deposits its energy as it travels through tissue. Alpha particles dump their energy in a short, dense burst; beta particles and gamma rays spread it thinly over a much longer track.

A PET or SPECT scan can make small tumours or lesions look fainter than they really are, simply because the scanner cannot see fine detail perfectly; the true 'brightness' gets smeared out over a wider area, especially in objects smaller than about 1-2 cm.

A check that the radioactivity in a vial really comes from the intended radioactive element, and not from some other radioactive contaminant left over from how it was made.

A measure of how much of a radioactive drug is genuinely radioactive versus how much is ordinary, non-radioactive filler of the same molecule. Higher specific activity means more radioactive atoms are packed onto the targeting molecules, so fewer 'cold' (non-radioactive) copies compete for the same receptors.

A more precise kind of PET scanner that measures the tiny difference in arrival time between the two flashes of light produced by each radioactive decay, which helps pinpoint where in the body the decay happened and produces clearer, less noisy images, especially in larger patients.

Removing the entire prostate gland and seminal vesicles for localised prostate cancer, now almost always with a robot.

Finding and removing the first one or two lymph nodes a tumour drains to, to see whether cancer has spread, instead of removing the whole nodal basin.

Injecting tiny radioactive glass or resin beads into the liver's artery so they lodge in the tumour and irradiate it from inside.

A rule that radiation should always be kept as low as practically possible, not just below the legal limit, taking into account cost, technology and benefit.

In the US, only a physician who has completed specific radiation training and case experience, and who is named on the clinic's license, is legally allowed to order and give radioactive drugs to patients.

A shielded instrument that measures exactly how much radioactivity is in a syringe or vial before it's given to a patient, so the dose matches the prescription.

The specially shielded room in a hospital or radiopharmacy where radioactive drugs are received, checked, prepared and measured before they are given to patients.

Any US clinic that wants to use radioactive drugs for patients must first get a specific license, either from the federal Nuclear Regulatory Commission or from the state government where it's located, proving it can handle the material safely.

After certain radioactive treatments, US rules set a specific radiation limit that must be checked before a patient can safely go home, and if the dose to a household member could exceed a lower limit, the patient gets written safety instructions (including, if relevant, guidance on breastfeeding).

Before any batch of radioactive drug can be given to a patient, it has to pass a checklist of quality tests, such as being the right radioactive strength, sterile, and chemically pure.

Every US clinic or hospital that uses radioactive drugs must have one named, specially qualified person responsible for making sure radiation is used and stored safely.

Radiopharmacy is the specialised branch of pharmacy that prepares radioactive drugs safely, correctly and on time, since these medicines decay and can't simply be reordered from a shelf.

Medicare's way of paying for a promising but uncertain test or treatment only for patients enrolled in a registry or study, used for PET scans in cancer from 2006 and now the frame for how Medicare covers gene panels and cell therapies.

Radioactive cancer treatments that circulate through the blood also irradiate bone marrow, so blood counts (red cells, white cells, platelets) can drop. Doctors check blood counts regularly and pause or reduce treatment if counts fall too far.

Sometimes an injected radioactive tracer or treatment leaks into the tissue around the vein instead of going into the bloodstream. For scanning tracers this usually just affects image quality; for treatment doses it can occasionally injure the skin and needs prompt attention.

Before a peptide receptor radionuclide therapy infusion, patients are given an IV drip of two amino acids, lysine and arginine, which reduces how much radioactivity the kidneys reabsorb and hold onto, protecting kidney function.

PSMA radioligand therapy can dry out the mouth because normal salivary glands pick up a small amount of the drug along with the tumour. It's very common but usually mild, and is one of the main reasons patients ask about the treatment beforehand.

A shortage of red blood cells or haemoglobin, causing tiredness and breathlessness. In cancer it comes from the disease itself (marrow infiltration, bleeding, inflammation), from chemotherapy suppressing the marrow, and from some targeted drugs.

The umbrella term for low blood counts of any kind (white cells, red cells, platelets) when treatment suppresses the bone marrow. Most chemotherapy causes it temporarily; radioligands, CAR-T and some pills cause longer-lasting versions.

Death of brain tissue months to years after radiosurgery or high-dose brain radiotherapy, which can look exactly like tumour growing back on a scan.

Too few platelets, the blood cells that form clots, caused by chemotherapy or by the cancer in the marrow. Mild cases cause bruising; severe cases (under 10-20 × 10⁹/L) risk serious bleeding and need platelet transfusions.

Most radioactive cancer treatments today give every patient the same amount, on the same schedule, regardless of body size. Researchers are testing whether measuring how much radiation reaches a patient's kidneys and tumours, and adjusting the dose accordingly, works better and is safer.

A matched set of two radioactive drugs built on the exact same molecule: one labelled with a radioactive tag good for taking pictures (a PET scan), the other labelled with a different radioactive tag good for treatment, so the scan predicts where the treatment will go.

Beta particles (lutetium-177) travel millimetres and are good for bulky disease; alpha particles (actinium-225) travel a few cells' width and kill with far higher energy.

The newer prostate cancer hormone pills (abiraterone, enzalutamide, apalutamide, darolutamide) that block the androgen receptor or the last steps of androgen production, used on top of standard testosterone suppression.

Measuring how much radiation dose each organ and tumour actually received from a radioactive drug.

The unit of radiation dose absorbed by tissue: one gray is one joule per kilogram. A curative course is typically 50-70 Gy in total; a single bone-pain treatment is 8 Gy. Radiopharmaceuticals are prescribed by activity in becquerels (GBq) instead.

Prostate cancer starts out fed by testosterone (hormone-sensitive) and shrinks when it is removed. When it learns to grow despite castrate testosterone levels it is called castration-resistant, a later and more dangerous stage with its own treatments.

How a drug moves through the body: how much is absorbed, how high the blood level gets, how long it lasts (half-life) and how it is cleared. These numbers decide the dose, the schedule and whether a pill can be taken with food or other medicines.

A radioactive drug for neuroendocrine tumours: a small peptide that homes to the somatostatin receptor on the tumour cells carries lutetium-177, which irradiates them from within. Given four times, two months apart.

Swallowing a capsule of radioactive iodine after thyroid surgery: thyroid cells (including cancer cells) are the only ones that soak up iodine, so the radiation destroys leftover thyroid tissue and metastases while sparing everything else. It was the first targeted radiotherapy, in 1946.

Using the same targeting molecule for a diagnostic scan and a therapy, so you treat exactly what you can see.

A complete response means every measurable trace of the cancer has disappeared on scans or in the marrow; a partial response means it has shrunk by at least 30% (RECIST) but is still there. Neither is the same as cure: microscopic disease can remain.

When patients in a trial's control arm are allowed to switch to the experimental drug after their cancer progresses. It is fair to patients but blurs the survival comparison, because the control group has now had the drug too.

An estimand is a precise statement of what question a trial is answering, including what to do about patients who switch treatment, stop early or start another drug; the ICH E9(R1) framework makes trials write this down before they start.