| Περίληψη: | Radiation therapy is a cancer treatment that utilizes high doses of radiation to eradicate cancer cells and shrink tumors. It damages cells by destroying the genetic material that controls how cells grow and divide.
The ability to calculate the absorbed dose before the treatment delivery by the treatment planning systems assisted clinical scientists and practitioners to predict possible overdose and underdose phenomena, maximizing the treatment outcome while causing less pain and discomfort to the patients.
Also, the treatment outcome can be improved, by increasing the reproducibility of the patient’s position. In radiotherapy, patients are treated on a couchtop device which is necessary to guarantee the proper treatment position. However, such devices have a dosimetric impact on the treatment outcome and may alter the dose distribution increasing skin dose while decreasing tumor dose. Furthermore, couchtops attenuate significantly photon beams.
In the current dissertation, the iBEAM Evo couchtop from Elekta was studied. The couchtop was incorporated in the Monaco TPS and our main objective was to find the optimum electron density values for the couchtop components (carbon fiber and foam core) for its proper modeling. The first chapter of this study analyzes the history of radiation therapy and refers to radiobiology principles. It focuses on the impact of couchtops in radiotherapy, introduces carbon fiber couchtops, and analyzes thoroughly the equations used in the study.
The materials used are introduced in the second chapter, and the experimental procedure is analyzed. A cylindrical phantom with an ionization chamber inside was used. Three energies were utilized (6, 10, and 15 MV) and dose values were measured at various posterior angles. A literature review of previous studies regarding electron density values was performed. Through trial and error, we found the electron density values that resulted in the optimum agreement between the measured and Monaco-calculated dose values. These results occurred by calculating the percentage deviation between the aforementioned values in the third chapter.
Moreover, a thorough investigation of the attenuation of the beam was carried out. We compared the measured and calculated attenuation values. These values were high enough to indicate the necessity of couchtop incorporation and proper modeling in Monaco TPS. Finally, we studied the relationship between the beam’s attenuation and the thickness of the couchtop.
|
|---|
