Radiotherapy Physics Group
About half of all cancer patients will receive external beam radiation therapy for their disease. One of the current challenges of radiotherapy for cancer is to improve its conformity, i.e. to cover the entire target volume with a high radiation dose, while exposing the surrounding healthy tissue as little as possible. This approach relies on the assumption that a reduction of the high-dose volume will lead to less normal tissue toxicity, which is indeed supported by a growing body of evidence. Consequently, the expectations for improved outcome have driven an extraordinary technical development aiming at increasing conformity. However, highly conformal treatment delivery techniques are generally accompanied by large volumes outside the primary target being exposed to low doses. Recent findings suggest that this so-called low dose-bath may be associated with an increased risk of adverse complications, both in terms of unexpected acute toxic effects and an increased occurrence of radiation-induced secondary malignancies later in life. Thus, it is important to aim at reducing the low dose-bath, without compromising the conformity, in order to continue optimising radiotherapy in the future.
The accurate delivery of external beam radiotherapy is challenged by changes in the patient geometry during the course of the treatment. Variations in patient setup between treatment fractions, and in particular, breathing movements during the treatments, result in a smearing effect on the dose distribution and deteriorate the conformity of the treatment. Furthermore, in dynamic intensity-modulated radiotherapy, the radiation delivery is modulated by moving the treament machine's gantry and collimators in an intricate pattern. Interplay effects between patient motion and the movements of these devices may lead to unexpected under- or overdosages in the irradiated volumes. For instance, in a tomotherapy treatment of a target with cyclic breathing motion, helical interplay effects may appear in the 3D dose distribution.
In order to ensure safe treatments, these interplay effects needs to be investigated and, if possible, acounted for. One vital component in this process is the development of adequate tools for 3D radiation dosimetry, i.e. the means required to determine the three-dimensional distribution of radiation dose inside the patient. Calculation models are important assets for this purpose. However, calculated dose distributions are associated with uncertainties, especially in the low-dose regions. There may also be systematic deviations due to inherent limitations of the calculation model and its implementation. Furthermore, the radiation delivery at the treatment unit may introduce additional uncertainties or deviations due to restrictions of the machine hardware. Thus, calculated dose distributions need to be complemented by experimental verifications. At present, the only existing method for true high-resolution 3D radiation dosimetry is the use of gel-detectors.
The radiotherapy physics research group at Lund University and Skåne University Hospital works in a clinical environment with state-of-the-art equipment for advanced radiotherapy, developing radiotherapy comformity while minimizing dose-bath and interplay effects, thereby aiming at an increasingly safe and effective radiation therapy for future cancer patients.
Hunor Benedek, PhD student, Hospital Physicist, SUS
Sven Bäck, Assoc Prof, Hospital Physicist, SUS
crister.ceberg [at] med.lu.se (Crister Ceberg, Professor, LU)
Sofie Ceberg, PhD, Hospital Physicist, SUS
Mårten Dalaryd, PhD student, Hospital Physicist, SUS
Anneli Edvardsson, PhD student, LU
Per Engström, PhD, Hospital Physicist, SUS
Mattias Jönsson, PhD student, LU
Tommy Knöös, Assoc Prof, Hospital Physicist, SUS
Ingrid Kristensen, PhD student, Oncology Nurse, SUS
Joakim Medin, Assoc Prof, Hospital Physicist, SUS
Per Nilsson, Assoc Prof, Hospital Physicist, SUS
Fredrik Nordström, PhD, Hospital Physicist, SUS
Elinore Wieslander, PhD, Hospital Physicist, SUS