radiation-wave1

Re-shaping the treatment plan to the anatomy of the day, using the images taken on the treatment couch, so the dose follows a shrinking tumour or a moving bladder.

A number for each tissue or tumour that says how much it cares about the size of each radiation dose. Low (around 2 to 3): very sensitive to big fractions, like the spinal cord and prostate cancer. High (around 10): mostly cares about total dose, like most tumours.

A way of converting any radiotherapy schedule into a common currency so that, say, five big doses can be compared with 25 small ones. EQD2 expresses the same thing as the equivalent total dose in 2 Gy fractions.

The machine that made curative radiotherapy widely available from the 1950s: a sealed cobalt-60 source in a rotating head. Linacs replaced it in rich countries, but cobalt units still treat many patients where power and servicing are unreliable.

Taking and holding a deep breath during each radiation beam. For left-sided breast cancer it pulls the heart away from the chest wall and cuts heart dose by about half.

Instead of one uniform dose, the plan gives more to the parts of the tumour that imaging says are most resistant, such as hypoxic or highly active regions on PET.

Tiny gold seeds or electromagnetic beacons placed in or near a tumour so the treatment machine can see exactly where it is each day.

The nested outlines a radiation plan is built on: the visible tumour (GTV), the tumour plus the tissue likely to hold microscopic spread (CTV), and a further margin for daily movement and setup error (PTV).

A tiny, intensely radioactive source is stepped through applicators placed in or beside the tumour for a few minutes at a time, then withdrawn, so the dose is delivered from inside without leaving anything behind.

Fewer, larger daily doses instead of the classic five to seven weeks of small ones. Large trials in breast and prostate cancer showed the same control with the same or fewer late effects and far less time in hospital.

Measuring the dose the patient actually receives, with detectors on the skin or the imaging panel behind them, to catch errors before they cause harm.

Software that learns from hundreds of past plans what dose distribution is achievable for a new patient, and produces a plan in minutes that a planner would have taken hours to reach.

Dozens of rice-grain-sized radioactive seeds are implanted permanently in the prostate in a single procedure and deliver their dose over months.

The healthy organs near a tumour that limit how much dose can be given, each with a maximum dose or dose-volume limit the plan must respect (for example, keeping the spinal cord below about 45 to 50 Gy).

How many times more radiation a cell without oxygen needs to be killed compared with the same cell with oxygen: about 2.5 to 3 for X-rays, close to 1 for the heaviest particle beams.

Modern proton machines paint the tumour spot by spot with a magnetically steered pencil beam, so the dose can be shaped in three dimensions and the proton's stop-point is put to full use.

Redness, dryness, itching and sometimes peeling of the skin in the treated area, building up over the course and settling a few weeks after it ends. Severe in a minority, worst in skin folds and after chemotherapy.

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.

Inflammation of the lung one to six months after chest radiotherapy, causing cough, breathlessness and fever; usually settles with steroids but can leave permanent scarring.

Using a tumour's gene expression or a patient's inherited variants to predict who needs more dose, who needs less, and who is at risk of severe side effects.

Drugs that shield healthy tissue from radiation: amifostine to protect salivary glands, palifermin for mouth ulcers, and newer agents aimed at the gut, lung and skin.

Drugs given with radiotherapy to make tumour cells easier to kill: cisplatin in cervical and head and neck cancer, temozolomide in glioblastoma, nimorazole for hypoxic tumours, and a new generation aimed at DNA repair.

About half the people who need radiotherapy will need it as part of curing their cancer, yet many countries have one machine per several million people or none at all. Closing the gap is one of the highest-return investments in cancer care.

Ways of dealing with tumours that move as the patient breathes: image the motion, treat only in part of the breathing cycle, hold the breath, or chase the tumour with the beam.

Radiotherapy can itself cause a new cancer in the treated area, typically ten to thirty years later. The risk is small for most adults but matters greatly for children and young adults.

Treating every visible metastasis with ablative doses when there are only a few, on the idea that some patients with limited spread can still be controlled or cured.

A single very high dose, or a few doses, aimed at a small brain or spine target with millimetre precision, replacing whole-brain radiotherapy for most brain metastases.

Low-energy X-rays that stop within a few millimetres, used to cure basal and squamous cell skin cancers where surgery would scar or is not wanted.

Cameras track the patient's skin surface in three dimensions during treatment, replacing tattoos and pausing the beam if the patient moves.

The equation radiotherapy uses to compare schedules: cell kill has a part proportional to dose and a part proportional to dose squared, and the ratio between them (alpha over beta) tells you how much a tissue cares about the size of each fraction.

Irradiating the whole body, or just the bones and marrow, to wipe out the patient's blood system and immune cells before a stem cell transplant.

A low-energy electron beam treats the entire skin surface, for lymphomas that live in the skin, without penetrating to the organs beneath.

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.

Cells short of oxygen are up to three times harder to kill with radiation. Finding hypoxic tumours and fixing the shortage, with drugs, breathing gases or dose escalation, is one of radiobiology's oldest ideas and still unfinished business.

The linac sweeps around the patient in one or two arcs while the beam shape, dose rate and speed all change, delivering an IMRT-quality plan in a couple of minutes.