Q&A
Dr. Arjun Sahgal
Dr. Arjun Sahgal is a scientist in the Odette Cancer Research Program at Sunnybrook Research Institute (SRI), associate professor at the University of Toronto and radiation oncologist at Sunnybrook Health Sciences Centre, where he is also the deputy chief of the department of radiation oncology. He spoke with Alisa Kim about his research.
Dr. Arjun Sahgal is a scientist in the Odette Cancer Research Program at Sunnybrook Research Institute (SRI), associate professor at the University of Toronto and radiation oncologist at Sunnybrook Health Sciences Centre, where he is also the deputy chief of the department of radiation oncology. He spoke with Alisa Kim about his research.
Illustration: Anthony Hare
What’s your research focus?
My focus is treatment and response assessment of brain metastasis (cancer that has spread to the brain from elsewhere in the body) with stereotactic radiosurgery. This entails using high-precision radiation focused on the brain tumour and delivering an ablative dose of radiation such that we maximize local control and minimize the dose to normal brain tissue. The aim is to avoid whole brain radiation, a more archaic form of therapy.
How does radiosurgery differ from conventional radiation therapy?
Conventional radiation involves low-dose radiation. It blankets all the tissue with radiotherapy, and therefore is not as targeted as radiosurgery. When you do target [the tumour] with precision radiation, there’s still a bit of low-dose exposure in normal brain tissue, but it’s clinically negligible. With radiosurgery, we’re using the most precise image-guided radiation technology to maximize the dose in the tumour and minimize the dose to surrounding normal tissue. We’re therefore allowed to deliver much higher doses than with conventional radiation—anywhere from two to six times higher. This means a transition from treating patients with locally palliative intent to locally curative intent.
Facts about radiation therapy in Canada
- About 50% of all patients with cancer receive radiation therapy.
- Radiation therapy is the main treatment for various skin cancers; cancers of the mouth, nose, pharynx and larynx; brain tumours; and gynecological, lung and prostate cancers.
- More than 100,000 radiation treatment courses are prescribed annually.
How does stereotactic radiosurgery work for planning and delivery?
It’s complex and time-sensitive, as treatment is focused on the tumour we see on magnetic resonance imaging. We need to make sure we have the radiation planned on the target before it changes [and] any tumour growth or bleeding occurs. It’s stressful because we need to image, plan and treat at the right time—from the same day for brain radiosurgery, to within five to seven days for spine. It’s a major undertaking—the clock is ticking and the pressure is on. Delivery involves multidirectional beams of radiation concentrating on the target, image guidance with cone-beam computed tomography, robotic couch-top technology and complex head immobilization devices. Radiosurgery requires medical physicists, therapists, radiation oncologists and dosimetrists to work together closely.
What has been your most interesting finding?
Thus far, the survival benefit of radiosurgery for younger patients. These data were presented at the [meeting of the] American Society for Radiation Oncology [in September 2013]. We’re completing the manuscript, which shows for the first time that by sparing the brain from radiotherapy and maximizing the dose to the tumour itself, patients may live longer because they’re not getting the toxicities associated with whole brain radiation. This could be practice-changing.
What are the next steps in your research?
One is treatment of multiple brain metastases with radiosurgery alone. It’s a new area and challenging because we’re dealing with 10, 15 or 20 [tumours] using a single treatment of radiation directed to each tumour simultaneously. That’s not an easy undertaking. We need to understand how to do it safely to minimize the risk of radionecrosis (tissue death due to ionizing radiation). We need a dedicated radiosurgery system that incorporates image guidance to figure out how to treat these patients efficiently, and to develop software to track the multiple tumours treated to monitor response and overall brain control. In addition, we want to incorporate novel sequences like those from the lab [of SRI scientist] Dr. Greg Stanisz, aimed at characterizing response right after radiation with respect to tumour cell death. That’s where development of software and imaging [technology] is going to come into play, in collaboration with SRI and the Odette Cancer Centre.
Sahgal’s research was funded by the Brain Tumour Foundation of Canada. For more on his research, visit sunnybrook.ca/research
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