Dr. Robert G. Bristow is the Director of the Manchester Cancer Research Centre (MCRC) at the University of Manchester in the United Kingdom.
Prostatepedia spoke with him about precision radiation therapy.
What is meant by precision radiotherapy?
Dr. Robert Bristow: There are at least two aspects to precision radiotherapy. The first is the “physical precision” of radiotherapy; the actual targeting of the radiation beams or radioactive compounds to the specific tumor tissues that you want to treat, with maximum protection to the normal tissues that surround that particular tumor. For example, external precision radiotherapy uses intensity modulated radiotherapy or proton therapy where you then deliver the radiation in very precise defined volumes.
The other type of physical precision in radiotherapy uses brachytherapy, actually placing seeds or catheters with radioactivity directly in the prostate and being able to conform the dose tightly to the prostate gland, with that dose falling off rapidly around the surrounding normal tissues that could acquire side effects (e.g. the bladder or rectum). The concept of physical precision has allowed us to increase the total dose to the prostate cancer and yet maximally spare the normal tissues from side effects.
Another aspect of precision radiotherapy is “biological precision” whereby we think about the entire treatment using radiotherapy based on the innate characteristics of a particular patient’s tumor.
This includes information about the genetics and microenvironment of the tumor cells within the cancer that make it uniquely suited to be cured by radiotherapy alone, or in combination with drugs that modify biology or the immune system.
This can have the effect of increasing the chance that the cancer is cured locally and also attack cancer throughout the entire body to kill what we call occult, or hidden, metastases.
Precision radiation therapy therefore now means both an understanding of the biology of the tumor in a specific patient as well as physics to optimally deliver that radiotherapy.
What role does functional imaging play?
Dr. Bristow: Imaging is a cornerstone for staging cancer and understanding its biology. It is absolutely required for staging patients to understand the anatomy of their cancer—not only where the local tumor is, but also the spread to the pelvic lymph nodes and beyond that to the bone, for example.
Anatomic imaging therefore gives us the geography of where those tumors are in the body. Functional imaging adds further components to start to understand the biology of those tumors. For example, by using functional imaging with MRI, we can look at differences in tumor blood flow, oxygen levels, or metabolically active versus metabolically inactive tumors.
For PET scanning, we can use specific radioactive tracers that will tell us about the glucose in the tumor, the amount of the tumor that has low oxygen status (called hypoxia), and the relative growth rate of tumors.
So imaging can now give us both anatomy and biology.
Totally different world, right?
Dr. Bristow: It is. If you understand the biology from the imaging and where things are, you can certainly target specifically those areas with precision radiotherapy using novel biological agents, which we call molecular targeted agents.