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Development of a new dosimetry technique

Tscharntke, Timo LU (2015) FYSM31 20151
Combustion Physics
Department of Physics
Abstract
In order to minimize the damage inflicted in healthy tissue during radiotherapy, it is vital to verify the dose absorbed by the patient. A common approach is the use of dosimetry gels in which local radiolysis processes are induced through radiation. As the subsequent read-out using Magnetic Resonance Imaging techniques is time-consuming, the here presented thesis investigates a new approach based on light scattering to determine the absorbed dose. More precisely, a laser sheet with sinusoidal intensity modulation is employed to scan the dosimetry gel slice-wise and scattered light is detected at a 90 degree angle which allows the determination of the local extinction coefficient in the sample. The idea is to relate the local extinction... (More)
In order to minimize the damage inflicted in healthy tissue during radiotherapy, it is vital to verify the dose absorbed by the patient. A common approach is the use of dosimetry gels in which local radiolysis processes are induced through radiation. As the subsequent read-out using Magnetic Resonance Imaging techniques is time-consuming, the here presented thesis investigates a new approach based on light scattering to determine the absorbed dose. More precisely, a laser sheet with sinusoidal intensity modulation is employed to scan the dosimetry gel slice-wise and scattered light is detected at a 90 degree angle which allows the determination of the local extinction coefficient in the sample. The idea is to relate the local extinction coefficient to the absorbed dose. In order to achieve this task, a setup for the data acquisition is built and the algorithm necessary for the calculation is written. Based upon first measurements investigating the applicability of the new approach, one can state that the new technique is of great potential as it allows the visualization of the irradiation structures with high resolution. (Less)
Popular Abstract
Radiotherapy is a common technique employed when treating cancer patients. However, the radiation can also potentially inflict great damage in the healthy tissue surrounding the tumor. Consequently, it is of great importance to verify that the radiation received by the patient is absorbed in the intended location and has the right dose. In order to implement such a so called dosimetric verification, a gelatine probe that behaves similar to human tissue when irradiated is produced. More importantly, the irradiation induces a change of structure in the gelatine sample which allows one to draw conclusions concerning the absorbed dose. Currently, the most common approach to determine the absorbed dose from structural changes in the gelatine is... (More)
Radiotherapy is a common technique employed when treating cancer patients. However, the radiation can also potentially inflict great damage in the healthy tissue surrounding the tumor. Consequently, it is of great importance to verify that the radiation received by the patient is absorbed in the intended location and has the right dose. In order to implement such a so called dosimetric verification, a gelatine probe that behaves similar to human tissue when irradiated is produced. More importantly, the irradiation induces a change of structure in the gelatine sample which allows one to draw conclusions concerning the absorbed dose. Currently, the most common approach to determine the absorbed dose from structural changes in the gelatine is to use Magnetic Resonance Imaging which is the same technique used to image tiny fractures in bones or to do brain scans. However, this technique also has a few disadvantages such as high costs associated with it as well as its time-consuming nature. Therefore, this thesis investigates a new approach to draw conclusions concerning the absorbed radiation dose from structural changes in the gelatine sample.

In this new technique, a blue laser beam is first compressed into a very thin sheet which is subsequently sent into the gelatine. The particles in the gelatine scatter light into all directions and a camera detects the amount of light that is scattered at a 90 degree angle. The brighter the image of the sample in a specific point, the more light has been scattered in that specific point. Most importantly, different structures in the sample scatter the light by different amounts. The laser sheet is then moved in steps through the gelatine, thereby scanning the whole sample. At each step, the camera acquires a new image which is employed to calculate a physical quantity called extinction coefficient for each point of the sample. The extinction coefficient describes how likely light is to be scattered when passing through a specific point in the sample. Thus, the value of this extinction coefficient depends on the structure of the sample and thereby also on the absorbed radiation dose. The work presented here aims to investigate the applicability of the new technique.

The result of this thesis work is a complete setup to acquire the data as well as the algorithm necessary to calculate the extinction coefficient in each point of the sample. Based on the results, one can state that the new technique is of great potential. Not only does it allow one to image the irradiated structures in the gelatine with a very high precision, it also shortens the time necessary for data acquisition as compared to other currently employed techniques. (Less)
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author
Tscharntke, Timo LU
supervisor
organization
course
FYSM31 20151
year
type
H2 - Master's Degree (Two Years)
subject
keywords
radiotherapy, dosimetry gel, extinction coefficient, light scattering, structured illumination, laser sheet, SLIPI
language
English
id
7470459
date added to LUP
2015-06-29 15:49:55
date last changed
2015-06-29 15:49:55
@misc{7470459,
  abstract     = {In order to minimize the damage inflicted in healthy tissue during radiotherapy, it is vital to verify the dose absorbed by the patient. A common approach is the use of dosimetry gels in which local radiolysis processes are induced through radiation. As the subsequent read-out using Magnetic Resonance Imaging techniques is time-consuming, the here presented thesis investigates a new approach based on light scattering to determine the absorbed dose. More precisely, a laser sheet with sinusoidal intensity modulation is employed to scan the dosimetry gel slice-wise and scattered light is detected at a 90 degree angle which allows the determination of the local extinction coefficient in the sample. The idea is to relate the local extinction coefficient to the absorbed dose. In order to achieve this task, a setup for the data acquisition is built and the algorithm necessary for the calculation is written. Based upon first measurements investigating the applicability of the new approach, one can state that the new technique is of great potential as it allows the visualization of the irradiation structures with high resolution.},
  author       = {Tscharntke, Timo},
  keyword      = {radiotherapy,dosimetry gel,extinction coefficient,light scattering,structured illumination,laser sheet,SLIPI},
  language     = {eng},
  note         = {Student Paper},
  title        = {Development of a new dosimetry technique},
  year         = {2015},
}