| 1. |
- Qatarneh, Sharif, 1972-
(författare)
-
Development of a Whole Body Atlas for Radiation Therapy Planning and Treatment Optimization
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of radiation therapy is to obtain the highest possible probability of tumor cure while minimizing adverse reactions in healthy tissues. A crucial step in the treatment process is to determine the location and extent of the primary tumor and its loco regional lymphatic spread in relation to adjacent radiosensitive anatomical structures and organs at risk. These volumes must also be accurately delineated with respect to external anatomic reference points, preferably on surrounding bony structures. At the same time, it is essential to have the best possible physical and radiobiological knowledge about the radiation responsiveness of the target tissues and organs at risk in order to achieve a more accurate optimization of the treatment outcome.A computerized whole body Atlas has therefore been developed to serve as a dynamic database, with systematically integrated knowledge, comprising all necessary physical and radiobiological information about common target volumes and normal tissues. The Atlas also contains a database of segmented organs and a lymph node topography, which was based on the Visible Human dataset, to form standard reference geometry of organ systems. The reference knowledgebase and the standard organ dataset can be utilized for Atlas-based image processing and analysis in radiation therapy planning and for biological optimization of the treatment outcome. Atlas-based segmentation procedures were utilized to transform the reference organ dataset of the Atlas into the geometry of individual patients. The anatomic organs and target volumes of the database can be converted by elastic transformation into those of the individual patient for final treatment planning. Furthermore, a database of reference treatment plans was started by implementing state-of-the-art biologically based radiation therapy planning techniques such as conformal, intensity modulated, and radiobiologically optimized treatment planning.The computerized Atlas can be viewed as a central framework that contains different forms of optimal treatment plans linked to all the essential information needed in treatment planning, which can be adapted to a given patient, in order to speed up treatment plan convergence. The Atlas also offers a platform to synthesize the results of imaging studies through its advanced geometric transformation and segmentation procedures. The whole body Atlas is anticipated to become a physical and biological knowledgebase that can facilitate, speed up and increase the accuracy in radiation therapy planning and treatment optimization.
|
|
| 2. |
- Adamus-Górka, Magdalena, 1977-
(författare)
-
Improved dose response modeling for normal tissue damage and therapy optimization
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis is focused on the development and application of dose response models for radiation therapy. Radiobiological models of tissue response to radiation are an integral part of the radiotherapeutic process and a powerful tool to optimize tumor control and minimize damage to healthy tissues for use in clinical trials. Ideally, the models could work as a historical control arm of a clinical trial eliminating the need to randomize patents to suboptimal therapies. In the thesis overview part, some of the basic properties of the dose response relation are reviewed and the most common radiobiological dose-response models are compared with regard to their ability to describe experimental dose response data for rat spinal cord using the maximum likelihood method. For vascular damage the relative seriality model was clearly superior to the other models, whereas for white matter necrosis all models were quite good except possibly the inverse tumor and critical element models. The radiation sensitivity, seriality and steepness of the dose-response relation of the spinal cord is found to vary considerably along its length. The cervical region is more radiation sensitive, more parallel, expressing much steeper dose-response relation and more volume dependent probability of inducing radiation myelitis than the thoracic part. The higher number of functional subunits (FSUs) consistent with a higher amount of white matter close to the brain may be responsible for these phenomena. With strongly heterogeneous dose delivery and due to the random location of FSUs, the effective size of the FSU and the mean dose deposited in it are of key importance and the radiation sensitivity distribution of the FSU may be an even better descriptor for the response of the organ. An individual optimization of a radiation treatment has the potential to increase the therapeutic window and improve cure for a subgroup of patients.
|
|
| 3. |
- Janek Strååt, Sara, 1977-
(författare)
-
Verification of high energy photon therapy based on PET/CT imaging of photonuclear reactions
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For classical and intensity modulated radiation therapy of deep-seated tumors, high-energy photons are the optimal radiation modality from an integral dose point of view. By using narrow scanned beams the treatment outcome can be improved substantially by delivering biologically optimized intensity modulated distributions often with sharp dose gradients. This requires using photons with energies well above 15 MV enabling verification of the treatment delivery in vivo by PET/CT imaging in a manner not previously possible. This new technique is based on the production of positron emitting radionuclides when the incoming high-energy photons interact through photonuclear reactions with the body tissues. The produced radionuclides, commonly 11C, 15O and 13N can then be monitored by PET and the distribution of activated nuclei show exactly where the radiation has penetrated the patient. In the subcutaneous fat, present in all humans, a high induced activity produces a perfect visualization of the location and even the intensity modulation of the incident beams. The reason for this is the high carbon content in combination with a low biological perfusion in fat tissues. Errors in the patient positioning such as setup errors or misplacement of the beams will thus show up in the PET images as a deviation from the actual radiation treatment plan. Interestingly, the imaged activity distribution from the subcutaneous fat also visualizes how the dose delivery can be deformed when the patient is erroneously positioned on the treatment couch as seen on the cover figure. Furthermore, the different half-lives of the produced radionuclides (20 min, 2 min, and 10 min, for 11C, 15O and 13N, respectively) allows for analysis of the dynamic behavior of tissue activity with the possibility of retrieving information such as tissue composition, biological and physical half-lives. The present thesis shows that considerable clinical information regarding the treatment delivery with high-energy photon beams can be obtained using PET/CT imaging. Although the study is based on the use of 50 MV photons the method may apply for beams with energies > 20 MV at higher doses.
|
|
| 4. |
- Östling, Janina, 1972-
(författare)
-
New Efficient Detector for Radiation Therapy Imaging using Gas Electron Multipliers
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Currently film is being replaced by electronic detectors for portal imaging in radiation therapy. This development offers obvious advantages such as on-line quality assurance and digital images that can easily be accessed, processed and communicated. In spite of the improvements, the image quality has not been significantly enhanced, partly since the quantum efficiency compared to film is essentially the same, and the new electronic devices also suffer from sensitivity to the harsh radiation environment. In this thesis we propose a third generation electronic portal imaging device with increased quantum efficiency and potentially higher image quality.Due to the parallel readout capability it is much faster than current devices, providing at least 200 frames per second (fps), and would even allow for a quality assurance and adaptive actions after each accelerator pulse. The new detector is also sensitive over a broader range of energies (10 keV - 50 MeV) and can be used to obtain diagnostic images immediately prior to the treatment without repositioning the patient. The imaging could be in the form of portal imaging or computed tomography. The new detector is based on a sandwich design containing several layers of Gas Electron Multipliers (GEMs) in combination with, or integrated with, perforated converter plates. The charge created by the ionizing radiation is drifted to the bottom of the assembly where a tailored readout system collects and digitizes the charge. The new readout system is further designed in such a way that no sensitive electronics is placed in the radiation beam and the detector is expected to be radiation resistant since it consists mainly of kapton, copper and gas.A single GEM detector was responding linearly when tested with a 50 MV photon beam at a fluence rate of ~1010 photons mm-2 s-1 during 3-5 μs long pulses, but also with x-ray energies of 10-50 keV at a fluence rate of up to ~108 photons mm-2 s-1. The electron transmission of a 100 μm thick Cu plate with an optical transparency of ~46% was found to be ~15.4%, i.e. the effective hole transmission for the electrons was about one third of the hole area. A low effective GEM gain is enough to compensate for the losses in converters of this dimension. A prototype for the dedicated electronic readout system was designed with 50 x 100 pixels at a pitch of 1.27 mm x 1.27 mm. X-ray images were achieved with a single GEM layer and also in a double GEM setup with a converter plate interleaved. To verify the readout speed a Newton pendulum was imaged at a frame rate of 70 fps and alpha particles were imaged in 188 fps. The experimental studies indicates that the existing prototype can be developed as a competitive alternative for imaging in radiation therapy.
|
|
| 5. |
- Danielsson, Mats, Professor, et al.
(författare)
-
Diagnostic and therapeutic detector system for imaging with low and high energy X-ray and electrons
- 2002
-
Patent (populärvet., debatt m.m.)abstract
- A detector unit for detecting photons in the energy range 1 keV to 100 MeV, includes at least two converter layers adapted to interact with incident X-ray photons and to cause electrons to be emitted therefrom, at least one amplifier adapted to interact with the electrons emitted from the converters and adapted to produce a multiplicity of secondary electrons and photons representing a signal proportional to the incident fluence of X-ray photons, a connector connecting the detector to an electric field generator providing an electric drift field for secondary electrons in the detector, and a sensor device arranged to receive the signal and provide an input to electronic signal processor.
|
|
| 6. |
- Górka, Bartosz, 1977-
(författare)
-
Development of tissue-equivalent CVD-diamond radiation detectors with small interface effects
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to its close tissue-equivalence, high radiation sensitivity, dose and dose-rate linearity, diamond is a very promising detector for radiation therapy applications. The present thesis focuses on the development of a chemical vapour deposited (CVD) diamond detector with special attention on the arrangement of the electrodes and encapsulation having minimal influence on the measured signal. Several prototype detectors were designed by using CVD-diamond substrates with attached silver electrodes.Interface effects in the electrode-diamond-electrode structure are investigated using the Monte Carlo (MC) code PENELOPE. The studies cover a wide range of electrode and diamond thicknesses, electrode materials and photon beam energies. An appreciable enhancement of the absorbed dose to diamond was found for high-Z electrodes. The influence of the electrodes diminishes with decreasing atomic number difference and layer thickness, so that from this point of view thin graphite electrodes would be ideal. The effect of encapsulation, cable and electrical connections on the detector response is also addressed employing MC techniques. For Co-60, 6 and 18 MV photon beam qualities it is shown that the prototypes exhibit energy and directional dependence of about 3% and 2%, respectively. By modifying the geometry and using graphite electrodes the dependencies are reduced to 1%.Although experimental studies disclose some limitations of the prototypes (high leakage current, priming effect and slow signal stabilisation), diamonds of higher quality, suitable for dosimetry, can be produced with better-controlled CVD process. With good crystals and a well-designed encapsulation, the CVD-diamond detector could become competitive for routine dosimetry. It is then important for correct dose determination to use a collision stopping power for diamond incorporating proper mean excitation energy and density-effect corrections. A new mean excitation energy of 88 eV has been calculated.
|
|
| 7. |
- Kempe, Johanna, 1977-
(författare)
-
Development of analytical transport methods for biologically optimized light ion therapy
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A general objective in the treatment of cancer is to eradicate the tumour cells without inducing severe complications in healthy normal tissue. The use of light ions for radiation therapy increases the possibility to deliver tumour suicidal doses with very low probability of normal tissue injury, not least in cases where the target is unresectable, radioresistant and located to near organs at risk. The success in the application of such beams in radiation therapy is largely determined by a thorough understanding of particle transport, biological dose response relations and their accurate integration in the treatment planning system. The focus has therefore been on the radiation quality of the light ions, their transport and to develop analytical tools and theories for their application in biologicallly optimized radiation treatment planning. New radiation quality results has been presented, new analytical approaches for the light ion transport in matter have been developed and new range concepts have been defined. A refined version of the Monte Code SHIELD-HIT was developed and used for calculating fundamental physical transport quantities that could be directly compared with the analytical theories and methods as well as with experimental data. The present results could be useful for biological optimized treatment planning, biologically optimized dose delivery techniques, dosimetry and for in vivo dose delivery verification.
|
|
| 8. |
- Nilsson, Johan, 1971-
(författare)
-
Accurate description of heterogeneous tumors for biologically optimized radiation therapy
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, a model of tissue oxygenation is presented, that takes into account the heterogeneous nature of tumor vasculature. Even though the model is rather simple, the resulting oxygen distributions agree very well with clinically observed oxygen distributions for most tumors and healthy normal tissues. The model shows that the vascular density may not describe the oxygenation of a tissue sufficiently well, unless the heterogeneity of the vascular system is taken into account. Based on the oxygen distributions from the tissue model, the associated radiation response at low and high doses can be determined. The radiation response of heterogeneous tumors should preferably be described by two clonogen compartments, one resistant and one sensitive, dominating the response at high and low radiation doses, respectively. Furthermore, each compartment should be characterized by the effective radiation resistance and the effective clonogen number. The resistant-sensitive model of radiation response has been analyzed in great detail. It accurately describes the response of severely heterogeneous tumors, both at low and high doses and LET values. The effective response parameters are given as integrals, averaged over the whole spectrum of radiation resistance. The parameters can also be determined from clinically established dose-response relations. The main properties of the dose-response relation for a generally heterogeneous tumor is described in some detail. The normalized dose-response gradient has been generalized to take heterogeneities in both dose delivery and radiation response into account. This quantity is important for accurate treatment plan optimization using intensity modulated radiation therapy for individual patients.
|
|
