Dosimetry: How to save lives with radiation

Simon Dobri

When I tell people that I am studying medical physics, I am almost always met with the question “Medical physics? What is that?”. There is no simple answer; any intersection of physics and medicine falls under the umbrella of medical physics. The field is incredibly broad and medical physicists have a wide variety of workplace responsibilities. However, a large number of medical physicists work in the fight against cancer, using the tools of medical imaging and radiation therapy. After reading this article I hope that you will know a bit about one important area of medical physics: dosimetry.

The goal of radiation therapy is to use radiation’s cell-killing properties to kill cancer while limiting the damage to healthy tissue, and fundamental to this is the practice of dosimetry. Dosimetry is the calculation and assessment of how much radiation dose is absorbed by the human body. In a cancer clinic, dosimetry is performed jointly by dosimetrists and medical physicists. Dosimetrists plan and monitor radiotherapy treatments to ensure that the correct dose of radiation is delivered, while medical physicists are responsible for taking the measurements that dosimetrists use for their calculations, and for developing the algorithms used in the treatment planning software. These measurements are performed according to rigid protocols. Refining these protocols to make measurements more reliable is a never-ending task for medical physics research.

Measuring radiation dose is a tricky thing to do. It requires specialized knowledge and the right tools. Radiation detectors used for dosimetry are called dosimeters, and developing new ones is an important job for medical physicists. Each dosimeter has its own advantages and disadvantages, and often the ideal dosimeter for a given situation hasn’t been built yet. My master’s thesis project focuses on the development of a new type of dosimeter that uses a laser to measure radiation dose. Its design, which is quite distinct from the existing options, makes it well-suited for a wide variety of situations. I hope to one day develop it into a commercially available product. I have even been discussing with my supervisor, Dr. Shirin Enger, the possibility of starting a company.

Acquiring accurate radiation dose measurements is only half the battle. The most significant biological effects of radiation stem from the damage that it does to DNA. Radiation kills cancer by damaging its DNA so much that it can’t survive, and it has the potential to cause cancer by damaging normal DNA such that it mutates and begins to replicate uncontrollably. Studying the extent and type of DNA damage caused by radiation is another job for medical physicists, a discipline that is known in the field as microdosimetry.

Dosimetry, along with medical physicists’ role in its study, is not limited to radiotherapy. It is also an essential part of radiation protection. Medical procedures such as x-rays and CT scans expose patients to ionizing radiation, and the dose that they receive from those procedures must be accurately quantified and minimized. People working with radiation, such as those in the nuclear energy industry and radiotherapy clinics, must be adequately protected and have their exposure levels carefully monitored. We must also keep an eye on our exposure to natural background radiation, such as that coming from radon gas and cosmic rays. Normally it’s nothing to worry about, but there are some situations where it can add up to the point that it becomes dangerous.  

Radiation is everywhere. It serves us all as a tremendously useful tool, but it can also pose a real threat to our well-being. Understanding its effects is a monumental undertaking, requiring new measurement techniques and technology, new theories, and countless experiments and computer simulations. Medical physicists are an important part of the team that is working towards this understanding, and harnessing its possibilities to combat cancer.