Recent advances in radiation therapy and photodynamic therapy

In the past 100 years, external beam energy for the treatment of cancer has continually evolved. Two main modes have been developed. The first is radiotherapy which involves using x-ray, gamma, and proton beams to cause ionizing damage. The second is photodynamic therapy, which uses photons to activate photosensitizers to generate reactive oxidating species causing cytotoxicity. For decades, these two fields have developed separately, with photodynamic therapy being used for treating surface tumors and radiotherapy, for deeper tumors. In the first half of this article, a detailed review of radiotherapy and photodynamic therapy will be presented. For each field, the underlying physical mechanisms will be discussed, followed by the existing technological and engineering designs, and ending off with the relevant vivo studies and clinical applications. In the second half, the recent efforts to combine radiotherapy and photodynamic therapy, leading to the generation of new techniques such as x-ray photodynamic therapy, proton-induced photodynamic therapy and even the possibility of hybrid approaches such as intensity and fluence modulated photodynamic therapy will be discussed. This new field is known as radiodynamic therapy. It has the potential to achieve increased conformality in the treatment of cancer, dealing maximal dosage to the lesion while sparing healthy tissues, paving the way for new advances in precision medicine. The connection between these fields is a neglected area, and this review addresses this gap. It also serves as a repository for researchers who are keen to venture into radiodynamic therapy.