SABR radiotherapy slashes the time needed to treat some early-stage prostate cancers – Cancer Research UK

Wielding SABR

SABR combines the power of multiple tiny, intense energy beams aimed at a tumour from different angles. These beams converge over the tumour, delivering a very high dose of radiation to cancer cells while minimising the impact on healthy cells.

Because of its pinpoint accuracy, SABR is especially suitable for treating small, well-defined cancers. It’s best known as a treatment for early-stage lung cancers that can’t be removed surgically. If a cancer has begun to grow or spread, standard radiotherapy is usually a better option, as its wider beams can kill cancer cells outside the tumour.

PACE B tested whether five sessions of SABR radiotherapy in a fortnight are as effective for treating low-risk, localised prostate cancer as 20 sessions of standard intensity-modulated radiotherapy (IMRT) delivered Monday to Friday for four weeks.

The results showed that the two treatments worked equally well, with more than 95 out of 100 men in the trial showing no signs of cancer five years later. Both came with a similar risk of causing side effects in the bowel or bladder.

Because it only takes a quarter of the sessions required for standard radiotherapy, SABR puts much less strain on people and the health service. If, as NHS England estimates, 1 in 5 eligible men choose it over standard radiotherapy, an extra 50,000 prostate cancer treatment appointments could be made available each year.

From two months to two weeks

PACE is led by researchers at the Royal Marsden Hospital and the Institute of Cancer Research in London. It’s the latest in a long line of trials we’ve funded to help make prostate cancer radiotherapy faster, more effective and more precise. Our CHHIP trial, which launched in 2002, even set the standard SABR is being measured against. 

CHHIP was an early study into IMRT, which also targets prostate cancer from different angles. The beams are larger and less powerful than those used for SABR, but each one is made up of many beamlets that can be turned up or down to focus the radiation on the specific shape of a person’s tumour.

This means IMRT can deliver a higher cancer-killing dose of radiation per session without increasing the risk of side effects, so effective treatments don’t take as long and the overall dose can be lower. CHHIP helped establish IMRT as the standard external radiotherapy treatment for prostate cancer, cutting the number of hospital trips needed to complete treatment from 37 (seven-and-a-half weeks of Monday-to-Friday sessions) to 20 (four weeks).

As well as making a profound difference to tens of thousands of lives, IMRT set the stage for SABR, which uses some of the same advanced radiotherapy machines and image-guidance techniques. IMRT’s beams are like an array of adjustable spotlights, but SABR’s are more akin to lasers, able to deliver much higher radiation doses with millimetre-level accuracy.

Now, PACE B has given men with low-risk prostate cancer a treatment option that is much easier to fit around the rest of their lives – taking just five sessions over a fortnight. And our researchers aren’t stopping there. For PACE C, they’re testing whether SABR could also make a similar difference for men with higher-risk prostate cancer, who are much more likely to need treatment to stop their cancer spreading.