Internal dosimetry on a macroscopic scale
Image based dosimetry is performed using an in-house developed programme package, which we call Lundadose. Currently, this program is used for dosimetry in clinical studies of 177Lu-Dotatate and 90Y/111In labelled Ibritumomab Tiuxetan, performed in close collaboration with Radiation Physics and the Clinic of Oncology, Skane University Hospital.
A screendump displaying the program for 3D adbsorbed dose calculation on a voxel level.
Lundadose contains methods for:
SPECT/CT voxel-based dosimetry, including:
- OSEM image reconstruction including detailed corrections for attenuation, scatter and collimator response, giving images in unit of Bq/voxel.
- A software for deformable image registration, since for some clinical studies image acquisitions are performed at 7 occasions distributed over a week. CT-CT image registration is performed, and then the spatial transformation is applied also to the SPECT images.
- A Monte Carlo program for calculation of the absorbed dose rate from the quantitative SPECT/CT images.
- For CT images: A calibration based relationship for converting from Hounsfield number to mass density.
Planar whole-body based dosimetry, including:
- Image-based activity quantification on a pixel-by-pixel basis, based on the conjugate-view method. The method includes attenuation correction by use of an X-ray CT scout image, and scatter correction by Wiener-filter deconvolution. Image analysis is performed by manual region-drawing, and applying corrections for activity in background tissues and in overlapping organs. Dosimetry is performed based on MIRD S-values.
- Image registration by a method tailored for whole-body images.
- Both SPECT/CT and Planar based dosimetry methods include:
- Curve-fitting procedures.
- A program for calculation of the biologically effective dose (BED).
- Bone marrow dosimetry is performed using based on blood sampling, and measurement of the activity concentration in whole blood and plasma using a well chamber.
- For 90Y Ibritumomab Tiuxetan treatments, image based dosimetry is performed both for planning of the absorbed dose prior to therapy using 111In, and for absorbed dose verification by 90Y-bremsstrahlung imaging.
- For 177Lu-dotatate, the BED is being calculated on a routine basis, as being the criteria defined for tolerance in a clinical study.
Image-analysis methods are being developed for automatic 3D SPECT-based image segmentation, and for correction of the partial volume effect in SPECT images. Moreover, pharmacokinetic and radiobiological modelling is being performed.
Katarina Sjögreen Gleisner, associate professor
Michael Ljungberg, professor