Anders Ahnesjö – Medical Radiation Physics

Radiation has many medical applications in both diagnostics and therapy. It has been estimated that approximately 1/6 the population in western countries will during their life get some form of radiation treatment. Our research focuses on the application of physics and engineering concepts to radiation in medicine in general, and specifically to improve radiotherapy to increase cure and/or reduce side effects.   

When ionizing radiation hits live cells it may cause damage and break the DNA strands. Most damage is repaired but for high doses the residual damage can be large enough to sterilize the cells. This is utilized for radiotherapy of cancer where various irradiation techniques are used to concentrate the dose to the tumour, sparing nearby tissues to reduce side effects.

External and internal radiation therapy

The radiation most commonly used for radiotherapy (RT) is photon beams produced by bremsstrahlung interactions in a high atomic number target irradiated by electrons from a linear accelerator. The photon beam is shaped by collimators and can be directed towards any chosen target in the patient. As the beam stems from a source outside of the patient this is also called external beam RT, contrary to brachytherapy where high activity, encapsulated sources of a radioactive material are placed in, or close to, the tumour.

External beam RT can also be given with beams of light ions, such as protons or carbon ions.

Light ion beams result in less dose to surrounding tissue

Photon beams penetrate all through the patient necessitating the use of cross fire techniques to achieve a therapeutic dose to the tumour. Light ion beams get absorbed and do not penetrate beyond a maximum range that can be controlled through the energy the particles has been accelerated to. Their dose yield increases towards the end of the range, the Bragg peak, enabling tumour sterilizing doses to be given with significantly less dose to surrounding healthy tissues.

Light ions are less used due to high investment costs. The Skandion clinic in Uppsala is a national facility for treating patients with proton beams.

Improved cure with reduced side effects

Successful RT is a compromise trying to maximize the probability for tumour control while keeping risks for severe side effects acceptable low.

In our research we apply a multiscale approach to improve methods and find strategies to widen the therapeutic window between cure and side effects. These range from nanoscale investigations of the implications in biological effect caused by variation in the texture of ionization patterns to the use of various means to improve the accuracy in patient positioning during irradiation.

We are also searching for methods to improve the use of computer simulations in the planning process of RT.

Schematic illustration of the radiotherapy optimization process.
   A physicist’s view of the radiotherapy optimization process.

More information about our projects

Read more about proton therapy