Targeted gene therapy in radiotherapy

Radiotherapy is the use of ionizing radiation in the treatment of malignant tumors. It is one of the main treatment modalities for many forms of cancer, with more than half of all cancer patients receiving radiation therapy at some point in their treatment.1 Biological and technological advances have brought notable improvements in radiotherapy over the years. Biologically based advances include improvements in fractionation schedules, treatment planning and combining radiotherapy with other treatment modalities such as surgical tumor debulking, chemotherapy and, most recently, gene therapy.1 Recent progress in diagnostic imaging, such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) and molecular imaging techniques, have led to the development of conformal (CRT) and intensity modulated radiotherapy (IMRT), which is the most advanced form of conformal radiotherapy. CRT and IMRT have enabled more precise dose delivery, conforming closely to the shape of the tumor and thus improving the therapeutic index;2 namely better local tumor control without compromising normal tissue. Although higher doses of radiation can produce better tumor control, the dose is limited by the possibility of normal tissue damage surrounding the tumor i.e. in the irradiation field. Despite a marked progression in the efficacy of radiotherapy, there is still a need for improvement of this treatment modality. Because radiotherapy is a local treatment, tumor cells outside the immediate field of radiation and those that have metastasized Radiol Oncol 2008; 42(3): 115-35. doi:10.2478/v10019-008-0009-1