Stereotactic Ablative Body Radiotherapy (SABR)
Our First Guest Blog for May 2014 is by Dr Shankar Siva, a Radiation Oncologist from The Peter MacCallum Cancer Centre in Melbourne. He discusses the new technique of Sterotactic Ablative Body Radiotherapy for kidney cancer in patients who are not medically fit for surgery. This new approach is still in a study period, but may offer cancer control to patients who do not have other treatment options.
Shankar, can you explain what Stereotactic Ablative Body Radiotherapy (SABR) is, and what advantages it has over other forms of radiotherapy?
Stereotactic ablative body radiotherapy (SABR) is a high precision radiotherapy technique that involves between 1 and 5 treatments. This is very different from conventional radiotherapy that involves daily radiotherapy for up to 8 weeks. It is non-invasive, painless, delivered without any need for anaesthetic, and conveniently does not require in-patient hospitalisation. SABR requires high-tech radiotherapy equipment for safe delivery, such as motion management for the tumour, accurate image guidance, and robust immobilisation. When delivered correctly, SABR can achieve submillimetre accuracy. Because of its precision, the SABR technique allows for much higher biological doses than can be safely delivered using conventional radiotherapy techniques. As such, most studies in sites such as the brain, lung and spine report cancer control rates in the order of 90% or greater after SABR.
Sterotactic radiotherapy for some other types of tumour has been around for some time. Why has it only recently been looked at for kidney tumours?
Stereotactic radiotherapy was first devised for brain tumours by Swedish neurosurgeon Lars Leksell in 1951, who termed it “radiosurgery”, so yes, it has been around for a very long time! Cranial "radiosurgery" was performed by using a rigid frame around the skull which allowed for accurate delivery of the radiation dose. However, tumours in other organs such as the lung, liver, and kidney are all highly mobile due to normal breathing or from the pumping of the heart. Only recently have technological advances allowed us to account for and manage tumour motion during radiotherapy delivery. The kidney in particular is a challenging organ, as it is quite mobile and surrounded by many sensitive organs.
Which group of patients is likely to be suitable for this treatment for kidney tumours?
Surgery is still the standard of care for patients with kidney cancer. However, kidney cancer is typically a disease of the older population, with the average age of diagnosis being 65 years of age. Some patients have other medical conditions which make invasive procedures potentially risky, particularly those patients who may have significant pre-existing kidney dysfunction, are risky anaesthetic candidates, or have heart disease and are reliant on blood thinners. In light of this risk, other procedures such as SABR and radiofrequency or microwave ablation have emerged as treatment alternatives for inoperable patients. In contrast to SABR, the disadvantage of radiofrequency ablation and microwave ablation is that those techniques can typically treat only treat smaller tumours, require the insertion of electrodes through the skin into the kidney (invasive), and are not as effective when tumours are close to blood vessels. On the other hand, the disadvantage of SABR is that it is typically restricted to patients who have not previously received radiotherapy to the upper abdomen. Otherwise, we expect that most patients who are not suitable for surgery on medical grounds may be eligible for treatment using the SABR technique.
What are the potential side effects?
In the early period after treatment, we expect that most patients feel tired. There may be some nausea, or loose bowel actions. Some patients may experience some reflux or heartburn. We typically prescribe preventative medications to help with these side effects. There may be a mild skin reaction, similar to a very light sunburn, particularly around the back. These side effects usually resolve within the first 2-3 weeks, and we expect all of these side effects to be resolved by around 6 weeks post treatment. The longer term effects of SABR in the kidney are less well understood. There is a potential for decline in kidney function, rise in blood pressure, scarring or narrowing of the bowel, or very rarely ulceration of the bowel or stomach. To date, studies have shown that the risk of severe side effects to be less than 5%.
This treatment is currently part of a study at the Peter Mac. What do you think the future holds for this treatment for kidney tumours?
We have pioneered this technique in Australia through the FASTRACK clinical trial, one of the few clinical trials using SABR for localised kidney cancer in the world. This study is expected to be complete later in 2014, and to date the results have been very promising. We would like to make this treatment accessible to all patients in Australia. However, the problem is that technology is very complex and varies from centre to centre. The Peter Mac is one of the largest radiation oncology institutions in the southern hemisphere and an Australian leader in the SABR technique, so we are not certain whether our results can be immediately reproduced in other institutions across Australia.
The next phase in our research program is to lead a multicentre study of SABR for kidney cancer involving multiple cancer centres across Australia. All the treatment plans will be centrally reviewed by our team at the Peter Mac for quality assurance, in order for this new treatment to be safely introduced across Australia. If this study is successful, I imagine that stereotactic radiotherapy will become a readily available treatment alternative for inoperable patients with primary kidney cancer.
Click this link to display a news item and video on the SABR technique.
Dr Siva is a Radiation Oncologist, Research Staff Specialist and NHMRC Scholar at the Peter MacCallum Cancer Centre in Melbourne. His major research interests are in high-tech radiation delivery and radiation biology. He is the lead clinician of the stereotactic body radiotherapy program at the Peter MacCallum Cancer Centre, and coordinates the first dedicated Stereotactic Ablative Body Radiotherapy (SABR) clinic in Australia. He published the first original research using the SABR technique in Australia. He serves on the Radiation Oncology Research Committee (RORC) of the Royal Australian and New Zealand College of Radiologists, on the renal subcommittee of the Australian and New Zealand Urogenital and Prostate (ANZUP) trials group, and as the radiation oncologist on the Management Advisory Committee (MAC) of the Australasian Lung Cancer Trials Group (ALTG). He is the principal investigator of multiple radiotherapy clinical trials of SABR in the context of lung, kidney and prostate malignancies.
Follow this link for more information on Dr. Shankar Siva