Anders Ahnesjö's projects in Medical Radiation Physics

Application of track structure-based modelling in proton and light ion treatment planning

Erik Almhagen, Nina Tilly, Anders Ahnesjö
Different radiation modalities such as low energy photons, proton beams or carbon ion beams, have different variation in biological response per dose. We have used a Monte Carlo track structure code, Geant4, to simulate event-by-event the energy deposition patterns for different radiation qualities used in radiotherapy such as photons, protons and carbon ions. Analyses of the energy deposition patterns in nano- and microscale yields event and energy deposition descriptors that correlates better to biological response effectiveness than the commonly used macroscopic quantity linear energy transfer (LET). We are now exploring potential avenues for incorporation of these findings into clinical practice, partly in collaboration with commercial vendors of software used in clinical radiotherapy.

Dose Painting – use of functional imaging for adapted dose prescriptions in proton therapy

Erik Almhagen, Alexandru Dasu, Anders Ahnesjö
We have developed a formalism for use of retrospective image data together with recurrence frequency of localized tumours for specific tumour sites to yield optimized dose prescriptions based on patient functional imaging, so called dose painting radiotherapy that potentially can raise the cure rate significantly. We now study how these processes can be adapted to ensure delivery robustness of such dose distributions for different types of radiation including scanned proton beams, partly in collaboration with commercial vendors of software used in clinical radiotherapy.

Interplay effects of scanned proton beams with patient movement

Nils Olofssson, Alexandru Dasu, Nina Tilly, Anders Ahnesjö
Modern proton therapy facilities apply a technique where a narrow beam is scanned over the tumour volume to be treated. A risk factor with scanned proton radiation is that patient movements during irradiation may interact with the scanning movement of the beams. These interplay effects may result in that parts of the tumour receive less than the planned dose, or parts of a nearby organ at risk gets overdosed. We are now extending these studies to lung tumours including the effects from the large variations in tissue density to evaluate optimal radiation strategies in collaboration with a group of university clinics through the Skandion network.

Application of optical body surface scanning in the thorax region

Kenneth Wikström, Ulf Isacsson, Anders Ahnesjö
A problem common for several radiotherapy scenarios is to establish the accuracy and precision with which practical motion indicators can be used for in-beam tumour positioning or out-of-beam protection of organ at risk. Photogrammetric methods using optical scanning of the body contour is a promising method, which is commercially available. We study the clinical applicability of such data in particular for two patient groups: left sided breast cancer where heart protection is crucial for prevention of heart complications later in life, and lung cancer as to precisely hit the tumour.

MR-Linac – integrated MR imaging during radiotherapy for target control

Adam Johansson, David Tilly, Samuel Fransson
The integration a treatment linac into a MR camera, a so called MRLinac, offers new possibilities for target identification and control during irradiation which can reduce the geometrical margins used to ensure dose coverage of the tumour. With smaller margins, less dose burdens are imposed on the healthy tissue also penetrated by the radiation. To enable use of real time imaging subsampling and artificial intelligence become necessary which are among the topics investigated in collaboration with the centre for image analysis, and the MRLinac vendor.