Radiation therapy (RT) utilizes the harmfulness of ionizing radiation for good, with the goal of destroying cancer cells without damaging too much healthy tissue. Dosimetry is always needed to achieve this goal. Dosimetry is a branch of physics the purpose of which is to quantify the amount of radiation energy absorbed by a mass, i.e., a dose. Dose measurement has always been the basis of safe RT, and knowledge of the properties of dosimeters used is essential to obtain the most accurate results. Radiophotoluminescence dosimeters (RPLD) made of phosphate glass use the luminescence phenomenon to quantify the absorbed dose. Monte Carlo (MC) simulations, the gold standard for dose calculation, has been used in dosimetry research for a long time. By combining these two methods, flexible and accurate measurements with calculated theoretical values providing valuable information for research can be obtained.

The aim of this thesis was to investigate the use of radiophotoluminescence (RPL) dosimetry with MC simulations for verification of the planned absorbed dose in different geometries and radiation treatment modalities and beam qualities. Each part of this thesis had two objectives, the first of which was to investigate the irradiation system, the treatment modality, or both, and the second of which was to investigate dosimeters and calculation. The measurements used different dosimetric methods to compare the results with RPLDs and/or MC simulations.

The results suggest that RPLDs are versatile and rather easy-to-use dosimeters that are suitable for many different purposes. Their small size and energy response must be taken into account when planning measurements. The accuracy of MC simulations is widely known, although the results can only be as accurate as the model used. When creating a phantom, even with extra care a perfect model cannot be achieved due to the random nature of the materials. Both methods, RPL dosimetry and MC simulations, have their strengths and weaknesses, but together they complement each other. The theme of the thesis can be considered timely; the results will contribute to a better understanding of the advantages and limitations of the dosimetry methods currently used and assist in the development of clinical RT treatments.