Computational radiation dosimetry, using e.g., Monte Carlo (MC) techniques, is used to calculate the amount of energy per unit mass deposited in tissue (the absorbed dose) resulting from radiotherapy and diagnostic radiology procedures. Motivated by the radiobiological importance of subcellular structures such as the nucleus, this work seeks to develop a better understanding of energy deposition on the cellular level.I would like to thank Dr. Rowan Thomson for being an excellent supervisor and mentor who is helpful, encouraging and inspirational. I would also like to thank Dr.Dave Rogers for helpful comments and suggestions related to cavity theory, and for being a wonderful teacher. Members of the Carleton Laboratory for Radiotherapy Physics (CLRP) are thanked for their support: