D.Tech. (Biomedical Technology) / Photodynamic therapy (PDT) is an alternative treatment modality for malignant tumours based on the photodamage to tumour cells through a photochemical reaction (Ahn et al., 2013). PDT utilizes a light sensitive photosensitizer (PS) that selectively localizes in tumour cells and is excited by light of a specific wavelength in the presence of molecular oxygen. The excited PS leads to the generation of singlet oxygen or other reactive oxygen species(ROS) which induces cytotoxic damage to cellular organelles and eventually cell death. Singlet oxygen has a very short life and its generation is controlled by the presence of the PS and the laser light (Senge and Radomski, 2013).The subcellular localization site of the PS plays a vital role in determining the effectiveness and the extent of cellular damage as well as the mechanism involved in cell death. Lung cancer is the leading cause of cancer death worldwide in both males and females, with an estimated 1.4 million deaths each year (American Cancer Society, 2011). Therapeutic modalities used in the treatment of lung cancer such as chemotherapy, radiotherapy and immunotherapy have rarely yielded a good prognosis and effective treatment remains a challenging problem to date. An alternative treatment modality with minimal complications such as PDT needs to be explored. Most in vitro PDT experiments are conducted on monolayer cultures and the cellular environment of these cultures does not correspond to that of in vivo studies. Multicellular tumour spheroids (MCTSs) serves as an important model in cancer research for the evaluation of therapeutic interventions since they mimic different aspects of the human tumour tissue environment.