Cancer and Radiotherapy

Abstract

Abnormal and uncontrolled growth of the cells can lead to cancer. In advanced countries, cancer is the second leading cause of death, and in our country, it is the third cause of death (after cardiovascular diseases and driving accidents). According to a report published by the Institute of Health and Evaluation (2015), for evaluating 32 cancers in 195 countries between 2005 and 2015, the prevalence of cancer has increased by 33% (1). Radiotherapy is one of the most common cancer treatments that can be used alone or in combination with other therapies such as surgery, chemotherapy or hormone therapy. Approximately 52% of patients with cancer have to be treated by Radiotherapy with a 50% contribution to treatment (2). Radiation therapy uses gamma rays or x-rays or accelerated particles to destroy tumor cells (3). In the past, radiotherapy was done in a two-dimensional fashion, using rectangular fields based on conventional imaging that has now been replaced with 3D conformal radiotherapy. In Three‐dimensional treatment, based on CT or other imaging methods, the treatment volumes such as: GTV (Gross Tumor Volume), target with microscopic spread of tumor that is CTV (Clinical Tumor Volume), ITV (Internal Target Volume), PTV (Planning Target Volume) and also related organs at risk are defined with high accuracy for treatment planning (4). In recent years, with the advancement of computer sciences in treatment planning systems, as well as accelerator equipment for delivering the dose to the patient, treatment can be applied as Intensity Modulated Radiation Therapy (IMRT). In IMRT, each radiation field consists of a beamlets and produces different intensities. This treatment is especially useful for curved areas and when the organs at risk are in the vicinity of the tumor. IMRT can be delivered using linear accelerators with static or Dynamic MLCs, Intensity Modulated Arc Therapy (IMAT), Volumetric Arc Modulated Therapy (VMAT) or tomotherapy (5). In determination of treatment volumes, the selection of appropriate margin is very important, because small margin may cause loos of the tumor and great margin can damage healthy tissues. The use of IGRT (Image Guide Radiotherapy) reduces these errors and increases the accuracy of treatment. Todays, in developed countries, SRT (Stereotactic Radiation Therapy) is used to destroy the non-surgical tumors, such as some of the brain tumors. In SRS, the prescribed dose is delivered to the tumor up to five sessions. In this method using imobilization devices is important, which usually involve the use of the relevant frames (6). In this regard, Cyber knife is actually a stereotactic system in which the x-ray source is mounted on a robot and can rotates in different angles. This treatment is based on three-dimentional imaging, so the tumor can be identified precisely with the guide of imaging. Cybernayev can be used to treat small tumors with high precision (7). In addition to treatment with X-rays, ions such as proton can be used to kill cancer cells. One of the important features of treatment with proton is the deliver of the absorbed dose of the particles into the tissue. The absorbed dose curve of this beam in the tissue has a peak at a specified depth, depends on the energy used, called the Bragg peak which can give the highest dose of radiation in the tumor site (8). There have been many advances in radiotherapy in Iran in recent years, but there is still lack of some advanced treatment equipment. On the other hand, with the regard of the significant cancer rate in the country, it is necessary to have proper information about the incidence of cancer at first. It should be noted that the use of registration systems based on just laboratory information (pathology) leads to a low number of cancer statistic, which this way is recorded in Iran. However, the cancer registry system in developed countries is based on clinical information and mortality in addition to collecting laboratory information. Another factor causing errors in the cancer record statistics is the population coverage of cancer registries; for example, population coverage in the United States is 99%, Australia and New Zealand is 86%, and the European Union is 57%, while coverage in South and central America is only 21% and in the African and Asian countries is 11 % and 8 %., respectively (1). Therefore, at first, it seems necessary to register the cancer properly in our country and then, based on the needs assessment for the different regions, establish and equipe radiotherapy centers.

Keywords

• Cancer
• Radiotherapy