Smarter radiation, fewer sessions: How SABR might help defeat metastatic cancer
February 13, 2020
Patients have had access to stereotactic ablative therapy (SABR) at UT Southwestern for more than a decade as a precision radiation treatment for a variety of cancers, including, lung and gastrointestinal tumors.
However, this type of therapy has mainly been used to treat the primary tumor, the site where the cancer first develops in the body. Now, we are seeing evidence that SABR also might improve survival for patients with metastatic cancer – tumors that have spread to other areas of the body.
SABR involves one or just a few high doses of radiation rather than the numerous smaller doses given in standard radiation treatment. It is incredibly precise – numerous radiation beams are focused directly into the tumor from various angles. SABR is so precise that very little tissue beyond the tumor receives toxic doses of radiation, which shrinks or destroys the tumor.
Equally importantly, SABR gives patients more control of their lives. Compared with traditional therapies, patients who have SABR can spend less time in the clinic – a precious benefit since cancer can make patients feel powerless at times.
At the Harold C. Simmons Comprehensive Cancer Center, we are a leader in the world for implementing, teaching, and researching SABR, particularly for metastatic cancer.
How SABR can be used in metastatic cancer treatment
Patients with metastatic cancer often are treated with medication such as chemotherapy, targeted therapy or immunotherapy. While both therapies continue to improve and evolve, they can’t fully control especially the visible tumors.
Surgery isn’t always an option, either. Tumors might be too difficult to reach, such as deep in an organ, or they may be in too many locations to remove in one procedure. SABR, also known as stereotactic body radiation therapy (SBRT), can be a precise and elegant way to eliminate or dramatically reduce secondary tumors so they don’t spread further.
Recent studies are showing promising results. UT Southwestern radiation oncologist Puneeth Iyengar, M.D., Ph.D., published a study in 2018 that found significant improvement in survival rates in patients with metastatic non-small-cell lung cancer who received SABR along with chemotherapy. The initial results were so impressive the trial was stopped early so all patients could access the therapy.
Another recent study showed improved survival rates for patients in Canada, Europe, and Australia with metastatic breast, colorectal, lung, and prostate cancers who received SABR. Confirmatory trials are ongoing to determine the benefits for specific types of cancer. In fact, Dr. Iyengar is leading one of these trials at UT Southwestern and nationwide, which is supported by the National Institutes of Health.
The SABR approach delivers precision cancer care
Dr. Robert Timmerman, Professor and Vice Chair of the Department of Radiation Oncology at UT Southwestern, is a nationally recognized expert in the use of SABR, a precise radiation technique that targets and shrinks tumors – and sometimes destroys them – all while damaging very little of the surrounding tissue.
Collaborating across specialties to fight cancer
When it comes to treating cancer, each patient and each tumor are unique. In one patient, surgery might be best to eliminate one tumor, SABR to shrink or destroy another, and immunotherapy to eliminate any remaining cancer. This type of mix-and-match combination requires close collaboration between specialists.
At UT Southwestern, we also work closely with our colleagues in imaging to provide just the right amount of treatment. In the past, radiation oncologists worked on a principle of "when in doubt, expand the field." This meant that healthy tissue was radiated along with the tumor.
The precision of SABR along with sophisticated imaging makes it possible to reduce the size of the target to just the tumor itself in many cases, sparing more healthy tissue and sometimes reducing or eliminating the need for subsequent chemotherapy.
The field is changing quickly, and doctors are learning new techniques – many of those from experts like ours at UT Southwestern. Our radiation oncologists regularly train physicians from around the world in the latest SABR techniques.
What’s next for metastatic cancer treatment?
Along with using SABR to treat metastatic cancers, we’re also looking at a new concept known as PULSAR, personalized ultra-fractionated stereotactic adaptive radiotherapy. This SABR-like treatment is tailored to each specific patient.
With SABR, those who need more than one treatment typically get it daily or every other day for a specified length of time. In PULSAR, treatment is more intermittent, such as every other week or once a month. Because the bursts of radiation are so strong, it’s unlikely that the tumor will progress between treatments.
This longer period between “pulses” allows us to observe the treatment's effect on the tumor. Some tumors just shrink away, while others will recruit defense mechanisms to hide from the patient's immune system. If we know how the tumor is going to behave, we can adapt the treatment to that specific response.
PULSAR clinical trials are just beginning, but we’re optimistic this approach will lead to another revolutionary change in cancer treatment. We also think patients will appreciate the practical convenience of PULSAR – instead of having to come in for daily treatments, they can schedule it better within their busy lives.
We’re also looking at whether SABR might induce an immune response similar to a vaccination. This has not been proven, but some small studies have indicated that SABR may have enhanced effects we never anticipated.
Along with the help of the brave trailblazers who participate in clinical trials, we look forward to continually improving cancer treatment for tomorrow’s patients. For information about whether SABR may be effective in your cancer treatment or for how you can join a clinical trial, talk to your doctor or search the clinical trials currently under way at UT Southwestern.