improve our understanding of radiosensitivity. In combination with the technological progress in radiation oncology, this new knowledge offers the potential to develop more specific targeted therapeutic strategies to optimize the curative principle of radiotherapy in the near future [I.4]. In addition, cancer genome analysis is expected to have a far-reaching impact on our understanding of cancer biology and will likely prompt new approaches to the detection, diagnosis, treatment and possibly prevention of the disease [I.5]. Through analysis of samples from early preinvasive lesions, from metastases, from recurrences after therapy, and from patients with known exposures or epidemiological risk factors, these studies should also provide insights into disease pathogenesis and progression, and mechanisms of radiation resistance. I.2. RADIOTHERAPY IN THE CONTEXT OF CANCER TREATMENT Radiotherapy and surgery are local, or locoregional, approaches to cancer treatment. As long as the cancer is localized to its site of origin or has spread to the regional lymph nodes only, there is a chance of curing the disease using a locoregional approach. However, the natural history of many forms of cancer has taught us that in many situations the cancer cells are not confined locally or regionally, although they appear to be so using currently available diagnostic tools. In these situations, diagnostic and staging tools show only local or locoregional disease, but in reality malignant cells have already escaped the locoregional boundaries and will eventually induce disease recurrence and possibly distant metastasis. In this scenario, local or locoregional therapies are clearly not enough, and the treatment of cancer requires a systemic approach involving chemotherapy, hormonal therapy or targeted therapy. Today, cancer patients who have access to the health care system are treated by a surgeon, a radiation oncologist, a medical oncologist or, preferably, a multidisciplinary team. The radiation oncologist, working in close collaboration with the other members of the radiotherapy team, is the physician responsible for prescribing, planning, monitoring and following the patient throughout and after a course of treatment with radiotherapy. Radiation oncologists make multiple decisions affecting the fate of their patients on a daily basis. Their responsibility as physicians is to provide clear and unbiased options, based on scientific evidence, for optimal patient care. 5 However, in the real world, their recommendations are also influenced by health economics, the managed care environment, local practice limitations, the desires of patients and families, and even politics. I.3. THE WORLDWIDE SHORTAGE OF RADIOTHERAPY The IAEA’s Directory of Radiotherapy Centres (DIRAC) [I.6] is the world’s authoritative source of information on radiotherapy centres. The DIRAC database counts more than 7600 radiotherapy centres, with about 13 000 teletherapy and 2600 brachytherapy machines serving the world’s population. These radiotherapy machines play an important role in the fight against cancer. Currently, the DIRAC database encompasses approximately 90% of the existing radiotherapy facilities, with comprehensive, up to date information for most countries. By offering a global assessment of the geographical distribution of radiotherapy facilities in relation to populations, cancer incidence and economic status, DIRAC offers a powerful tool for understanding the current trends in the accessibility of radiotherapy, as well as for planning future radiation oncology services. DIRAC’s global survey shows a dramatic discrepancy in the ability of cancer patients to access lifesaving radiotherapy across countries and regions of the world (see Chapter 5). In high income countries, one radiotherapy machine is available for every 120 000 people. In middle income countries, one machine serves over 1 million people. In low income countries, about 5 million people rely upon a single radiotherapy machine. In 51 countries, independent territories and islands, cancer patients have no access to radiotherapy; of these countries without radiotherapy services, 29 have populations of over 1 million people. To approach the