Radiation therapy is a precise science – one Engineering professor Kibret Mequanint aims to fine tune.
Nearly 200,000 Canadians are diagnosed with cancer each year, according to the Canadian Cancer Society. The ailment is considered the leading cause of premature death in the country.
The standard course of treatment for cancer patients includes surgery to remove a tumour, radiation therapy, chemotherapy, or any combination thereof, noted Mequanint, whose work focuses on the design and development of materials for biomedical applications. Approximately 50 per cent of patients will end up receiving radiation therapy.
But the current methods used to determine their treatment plans aren’t entirely effective.
“A radiation oncologist will prescribe a certain dose (of radiation) for the tumour using fractionation – they fraction out the total dose of radiation because patients can’t handle the entire dose in one shot,” Mequanint explained.
A patient could receive a prescription totaling 20 gray (Gy) – the unit used to measure radiation – to target a tumour and could have 10 treatment sessions of 2 Gy each.
Doctors don’t want to do more harm than good, Mequanint explained, so radiation physicists consider the prescribed dose and use imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT) to assess the volume of the tumour and determine the exact amount of radiation required, as well as its exact location.
“You know how much radiation is required to shrink or destroy the tumour, but you have to be careful that you don’t target vital organs or healthy tissues. What has been challenging is determining how much of the delivered dose ends up going to the target volume – the tumour,” Mequanint said.
This is where his lab comes in.
Current methods of measuring delivered radiation leave patients exposed to an increased risk of systematic and random errors, which are difficult to quantify, Mequanint said. His lab was approached by a medical device company and tasked with creating a hydrogel dosimeter – something that would help radiation physicists and oncologists measure, in 3D, the dose and distribution of radiation applied to a tumour.
“You have a gel in a jar, and you take this jar and deliver the exact dose of radiation you plan to deliver to the patient to the gel. After you (irradiate the gel, inside the jar), you take it out and then you image it and measure where the radiation is distributed. You can translate that into a patient’s treatment plan,” Mequanint explained.
In 2008, his lab started the work and has since developed a hydrogel that is proving its effectiveness in lab settings. The hydrogel dosimeter, which basically looks like a jar of jelly, is mostly made up of water. Molecules that make up the gel react to radiation and change in colour, showing the location of radiation delivered.
In essence, the gel is a surrogate for a cancer tumour, Mequanint explained. Once a medical team irradiates and images the gel, doctors are able to develop a more precise treatment plan for a cancer patient because they have a more precise idea of where radiation will be delivered.
“There are other gel systems right now and at least two to three companies who claim they have gels that can measure the delivered dose, but they have their own challenges,” Mequanint noted.
Other gel systems are comprised of molecules that are so sensitive to radiation they react and move away from the site where they received it. This means by the time a medical team images the gel to see where the radiation went, the molecules have moved, yielding an inaccurate model for a patient’s treatment plan.
“You can’t say that the radiation was delivered to the correct location,” Mequanint said.
His lab has solved this problem and has developed a more stable gel. But there’s more.
“Clinically, the imaging of the irradiated gel is done by MRI and that is very expensive; it takes time. What we needed to do was develop an inexpensive imaging system,” Mequanint continued.
“If we can design the gel to become transparent before and after irradiation, we can use optical methods, which are inexpensive compared to MRI, to image it.”
His lab has likewise succeeded in this and Mequanint believes his is the first to do so. He has licensed his dosimeter to a medical device company who is making the hydrogel on a pilot scale and distributing samples to cancer centres around the world.
“They are getting good feedback and now, we’re continuing to Phase 2 to make it even better,” Mequanint said, noting his lab is looking at ways to reuse the gel.
At $350-500, a one-litre jar is expensive and could be cost-prohibitive in treatment plans. His team is looking to see if a dosimeter could be used two-three times.
“We have data that shows we could be able to do it and that’s where we are heading.”
