Image quality measures in proton computed tomography.

摘要

Proton therapy is an external beam radiotherapy that uses proton beam as ionizing radiation to treat localized tumor cells within the human body. The calculated proton beam range is used to locate and damage the DNA of cancerous tissue, thus, leading to cell death. Due to the Bragg peak characteristic of protons, the range of proton beam in matter can be calculated accordingly which offers greater degree of conformal dose delivery than conventional X-ray beam therapy. Currently, the treatment planning of proton therapy is based on the X-ray computed tomography (CT) scans of the patient anatomy. The images reconstructed from the xCT scans relies on the calculation of photon relative linear attenuation coefficients called Hounsfield units (HU). Proton treatment planning involves converting attenuation coefficients from xCT scans to relative stopping power (RSP). This conversion procedure results in range uncertainties in pre-treatment room. Therefore, a new imaging procedure is needed that can directly calculate the reconstructed RSP values of each patient and this is the aim of proton computed tomography.;Proton computed tomography (pCT) is a medical imaging procedure that has the potential to improve and better the currently existing proton therapy treatments. The proper implementation of pCT would resolve the discrepancies in converting attenuation coefficients to RSP values by directly calculating the reconstructed proton RSP distribution. This leads to the reduction of uncertainties in the RSP values of tissues, decreased irradiation to healthy tissues, greater degree of conformality and improved patient position in the pre-treatment room. However, the main objective of this thesis is to better understand the image reconstruction method in pCT by studying the image quality measures in pCT scans, and investigating methods and strategies to improve reconstructed image quality with an eye on proton treatment planning.