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Radiotherapy, refers to using radiation to eliminate tumors. Radiotherapy as an important way of treatment of malignant tumors, for many cancers can produce good results. In this paper, the history and physical principle of radiotherapy can be introduced. And the technology and equipment of radiation is used will be introduced, include some technical background to the equipment. And then some clinical applications will be presented and show if these applications are useful, such as treatment in salivary gland tumor, small-cell lung cancer. Finally the risk of this technology should be presented for safely use of the radiotherapy.
Key word : radiotherapy, tumor, physical principle, salivary gland tumor, small-cell lung cancer, risk.
There are two types of tumors which one type is called benign tumor and the other is malignant tumor. And cancer is one kind of malignant tumors which can be cured difficultly. Malignant tumors from histology can be divided into two categories: one occurrence of the malignant epithelial cells is known as cancer, such as malignant lung epithelial cells to form lung cancer, malignant gastric epithelial cells to the formation of gastric cancer, and other one from malignant transformation of leaf tissue is called sarcoma, such as leiomyosarcoma, fibrosarcoma. A human cell has a process of growth, reproduction, aging, the dying. Cell death after aging will be replaced ith new cells to maintain normal function of tissues and organs. But cancer is not like that, it can grow all the time and consume a large number of nutrients. Also, cancer cells can release a variety of toxins, producing a series of symptoms in human body.
And for treating the cancer, there are many ways used such as surgical operation, chemotherapy, radiotherapy. And radiotherapy is the most common way to cure cancer. Radiotherapy is the use of radioactive isotopes produced by radiation such as Î±, Î², Î³-rays and treatment of various types of x-ray machine or accelerator x-ray, electron beam, proton beam and other particle beams such as a method of treatment of malignant tumors. Since19th century, the discovery of radium and X ray, radiation treatment of malignant tumors has been used very significant development. Now commonly used in clinical radiation therapy in vitro and in vivo can be divided into two types, the former application of X ray therapy machines, cobalt 60 therapy unit for treatment, or a neutron accelerator, which is applied for treatment of radioactive nuclides. And now about 70% of cancer patients during the treatment of cancer need radiation therapy, about 40% of cancer can be radical radiotherapy. Radiotherapy in cancer therapy have become increasingly prominent role and status. Radiotherapy has become one of the primary means of treatment of malignant tumors. Radiotherapy has only a few decades, but developed rapidly. As the use of ultra-high pressure treatment machines, auxiliary tools and experience to improve the treatment effect has been significantly improved cancer treatment has become the most important means. Of about 70% of cancer radiation therapy required, the U.S. statistics there are more than 50% of cancer radiation therapy required. Radiation therapy for virtually all of the cancer treatment for many cancer patients, radiation therapy is the only method of treatment must be used.
Radiotherapy is x ray, Î³ ray, electron beam irradiation in cancer tissues, etc., due to biological effects of radiation, to the greatest number of anti-cancer tissue, cancer tissue damage, making it smaller. This therapy is the use of the lethal effects of radiation on cancer therapy, due to sufficient radiation dose is to be irradiated sites only to have a therapeutic effect, therefore, is the same and surgical therapy for local treatment. As a result of radiotherapy, but also treatment of cancer, symptoms can improve, but also prolong life is the best desired result, which is understood as indications of radiotherapy. The sensitivity of cells to radiation is of the highest in the division, DNA synthesis in the lowest of its sensitivity, it is clear. Radiation therapy is less normal tissue injury, is only given to a large number of abnormal proliferation of anti-cancer, so narrow, but again as far as possible to maximize the body's regulatory function. Recently, in order to impact as little as possible to the surrounding normal tissue, it exposes the the lesions from multiple direction method. This sub-radical radiation therapy is divided palliative radiation, radiation therapy and radiotherapy with surgery. Currently, in addition to high energy x ray, Î³ ray, the line started to use high-energy particle radiation for cancer therapy. This method can be expected in future radiotherapy method in a more important role to play. History of radiation therapy is only 80 years, but has developed rapidly, from the X-ray machine to a high pressure device, the acceleration of the current updated constantly improve, and the emergence of proton radiation and negative Ï€ mesons, and other special radiotherapy.
Equipment of radiotherapy
X-ray treatment machine
X-ray treatment can be divided into X ray machine (10KV ~ 60KV), superficial treatment machine X ray (60KV ~ 160KV) and deep X ray therapy unit (180KV ~ 400KV) by different energy rays. X-ray treatment machine drawback is low energy, through weak, the skin affected by volume, has been less used.
Modern radiotherapy departments use linear accelerator, which is used to produce x-rays of energies of 6-20 million electron volts (MeV). There are major clinical advantages with such x-ray over low energy x-rays generated by older kilovolt machines. Mega-voltage x-rays are relatively 'skin-sparing'. Deep-seated tumours can be fairly easy to treat with a homogeneous radiation beam and the radiation dose to surrounding tissues lower than the bone. Older kilovolt apparatus generates x-rays of 100,000-300,000 electron volts (KeV). X-ray produced by these machines is only 2-3 times more energetic than those used to take diagnostic radiographs. The maximum energy of the kilovolt x-rays is deposited on the skin surface, this means that this kind of X-ray is useless in treating deeper tumours and at least they are limited. At present, these machines are used for low-dose palliative treatments or for the treatment of skin/superficial tumours.
Radium 226, the natural sources, because of its long half-life, is now available for artificial radionuclides 60 Co, 137 Cs, 192 Ir replaced. Radionuclides can radiate three kinds of rays as a, ß, r-ray, clinical ß-ray only for the treatment of superficial tumors, r-ray radiation therapy as the main sources of energy 1.25MeV. Radiation therapy machine is made with cobalt 60, for r-ray penetrating power, high dose of deep, less affected by the skin. It can be used in the treatment of deep tumors.
The interaction of radiation with tissues is measured as the absorbed dose, which is the quantity of energy absorbed per unit mass. In the SI system of units this is measured as joules per kilogram. One joule per kilogram is 1Gy. One Gray is equal to 100 rad (the previous unit for radiation dose). The limitation on radiation dose, when given in an attempt to cure a tumour, is the risk of normal tissue damage. This damage is seen initially as acute radiation effects in rapidly proliferating cells such a skin epithelium, mucosal lining of the upper digestive tract, or the surface lining of the small bowel. This may manifest itself as moist desquamation of the skin, mucositis inside the mouth or diarrhoea caused by damage to jejunal crypt cells. This damage normally heals. The greater concern is the risk of late damage to normal tissue. This appears 9 months to 5 years after treatment due to effects on slowly proliferation tissue, particularly vascular endothelium. This is expressed as progressive fibrosis and arteritis leading to necrosis, fistulae or stricture. The serious complication rate for patients treated for carcinoma of the cervix by radical radiotherapy is about 5%. This is one of the highest complication rates in clinical radiotherapy.
Application of radiotherapy
Small-cell lung cancer (SCLC) accounts for approximately 13% of all lung cancers and the incidence in women relative to men has risen over the last decade . SCLC is considered to be a radiosensitive disease . However, a high frequency of local failure has associated with low dose schedules. Furthermore, retrospective studies suggest that progression-free survival can be improved by translating thoracic radiotherapy doses of 50 Gy or more  but an impact on overall survival has yet to be demonstrated. In a phase I study of thoracic radiotherapy given concurrently with platinum and etoposide, the maximum tolerated hyperfractionated dose was 45Gy in 30 fractions over 3 weeks for twice daily radiotherapy, and 70Gy in 35 fractions over 7 weeks for daily radiotherapy. The dose limiting toxicity was grade 4 oesophagitis. The advantage of delayed radiotherapy includes the possibility of irradiating a smaller volume of normal tissue if the post-chemotherapy volume is treated, resulting in less toxicity. Furthermore, the increased toxicity associated with early concurrent treatment could compromise the chance of maintaining the dose intensity of the chemotherapy and/or the total number of cycles delivered. Comparing the nine clinical trials' results, the best results have been seen with early concurrent thoracic radiotherapy. The 20% 5-year survival milestone has generally been achieved with early thoracic irradiation. Several meta-analyses evaluating the timing of thoracic radiation in combined modality therapy have been published. Fried et al. demonstrated a 2-year overall survival benefit for early thoracic radiotherapy compared to late thoracic radiotherapy of 5.2% (95% confidence interval (CI) 0.6-9.7%, p = 0.03). Important progress has been made over the last 2 decades in the management of small-cell lung cancer as a result of advances made in the understanding of the role of chemoradiotherapy and the optimisation of its delivery. However, some important questions remain unanswered. In order to test new chemotherapy regimens and targeted therapies in combination with thoracic radiotherapy, there is a need to establish a standard of care in LD-SCLC. The role of thoracic radiotherapy in ED-SCLC needs to be determined. For the future, ongoing translational work will aim to establish predictive biomarkers of chemotherapy and radiotherapy sensitivity to allow for individualized treatments of small-cell lung cancer.
3.2 Oral and maxillofacial malignant tumor
General oral and maxillofacial malignant tumors are cured by external radiation, within the time of irradiation as a complementary treatment of residual tumor. There are five main ways to treat the oral and maxillofacial malignant tumor. 1. Brachytherapy: Modern brachytherapy has been widely used to treat various parts of the tumor, mainly used in conjunction with external beam radiotherapy or surgery. Little oral and maxillofacial malignant tumors is treated by Brachytherapy,, only a small number of early oral cancer does. Brachytherapy treatment can develop the efficiency of treatment and using high activity micro-stepping radioactive sources also provides the conditions for dose optimization. CT guided by ultrasound or stereotactic implantation can greatly improve the traditional template-type implantation, and to avoid the pin stab wounds caused by large blood vessels or damage vital organs. 2. Dimensional conformal radiotherapy and intensity modulated radiation therapy: Three-dimensional conformal radiation therapy is a modern high-precision radiotherapy techniques, body position must be repeated to ensure the accuracy of radiotherapy, to prevent displacement of radiotherapy patients. Vacuum body modes, thermoplastic surface modes are commonly used fixtures . In the conformal technology, thermal cut wire cut foam for domestic use, infusion of low dissolved lead block hole is a mature technology, but the accuracy worse. Radiation therapy equipment for the old electric or manual can also be plug-MLC (multileaf collimator, MLC). Since conformal radiotherapy improves target dose, can improve local tumor control rate, while reducing radiation to normal tissue complications and improve quality of life of patients after radiotherapy. The patients who have the main failure of local control and distant metastasis of the tumor using conformal radiation therapy can improve their survival rate. 3. Stereotactic radiotherapy: Stereotactic radiotherapy is a modern precision radiotherapy techniques, a good local treatment, but it is actually not a "knife ", it can't replace the "knife" Positioning accuracy and the use of its superior physical characteristics of the dose distribution, can, were more limited intracranial disease, oral and maxillofacial and other body parts to local treatment failure in patients with malignant tumors based benefit, but should not exaggerate the efficacy and abuse in order to avoid Increase the economic burden of patients and even cause adverse effects. 4 Radiation therapy and chemotherapy combined treatment: The purpose of concurrent chemotherapy and radiotherapy is to produce superimposed or synergistic effects between the two. The theoretical basis is: chemotherapy agent against tumor cells after sublethal radiation damage or the repair of potentially lethal damage. Adjusted chemotherapy tumor cell growth cycle and improve the radiation-sensitive phase of the cell ratio. Reduce mass, improve blood supply, increased radiation sensitivity and chemical sensitivity. Some chemotherapy drugs are radiosensitizer as the effect of the radiation sensitizing. Radiation increases the local concentration of chemotherapeutic drugs. 5. Radiation therapy and surgery integrated treatment: In the treatment of advanced oral cancer strategy is planned to be combined therapy, combined radiotherapy and surgery is an effective treatment for oral cancer. Preo-perative radiotherapy can make the tumor shrink, reducing the scope of surgical resection, organ retention unresectable disease can be converted to be surgery. At the same time it can reduce the intraoperative disseminated cancer cells grow and the recurrence and metastasis. The advantages of preoperative radiotherapy is, tumor shrinkage after radiotherapy, easy to surgical resection, so that part of the original can't be completely removed or difficult to complete surgical resection. In addition, the active radiation on tumor cells and tumor-killing outside the sub-clinical lesions, reducing the risk of surgery in the cancer cells grow and spread opportunity to blood, thereby reducing the local recurrence and distant metastasis rates.
For treating breast cancer, there are several ways for different phases of breast cancer. 1. For early stage breast cancer, Keeping breast conserving surgery and radical radiotherapy in the treatment of combination therapy has become one of the main methods of early breast cancer. Many researches have proved that, whether it is long-term survival, or local control rate, this treatment with radical or modified radical mastectomy the same, and cosmetic results satisfactory. In this paper, we just talk about the radiotherapy for keeping breast surgery. This therapy choice the 60Co and 4-6Mv X-ray as the radiation source. Breast-conserving surgery and radiotherapy effect, the local recurrence rate is different in each report, but generally between 1% and 10%. Local recurrence caused by many factors. Local recurrence can still salvage therapy for radical surgery, the long-term survival rate after treatment is still high, each reported in 62% to 85%. Early stage breast conserving surgery plus radiation therapy technology has been quite mature, with the accumulation of clinical experience and development of this therapy will be more perfect. The direction of its development is: Firstly, to adapt to further expand the scope, from the early breast cancer extended to the locally advanced breast cancer; the second is more refined treatment methods and technology, more effective. Locally later stage breast cancer also can use radiotherapy to cure. But as the amount of radiation in locally advanced breast cancer is relatively high, often severe fibrosis, causing impairment of shoulder mobility; place soft tissue or bone necrosis, fracture; also possible lung injury, upper extremity edema, and damage the brachial plexus. Locally advanced breast cancer radiotherapy is not an ideal method of treatment.
Risk and complication
Although there are many advantages using radiotherapy and chemotherapy comprehensive, but also many disadvantages. Radiotherapy can reduce the toxic effects of chemotherapy, chemotherapy can't reduce the effect of radiation damage, such as systemic chemotherapy, bone marrow suppression, radiation also produced partial bone marrow suppression, patients are often compared because of low blood, bone marrow suppression can't continue treatment. When doing the breast cancer radiotherapy, chemotherapy or radiation pneumonitis after pulmonary fibrosis patients changed significantly increased the incidence of radiation pericarditis, sometimes have to reduce the radiation dose, increasing the difficulty of radiotherapy. Chemotherapy on the gastrointestinal tract toxic liver and kidney, radiation damage to these parts is quite large, so the combined treatment, the radiation dose is considerably limited, is not difficult to improve the sensitivity of the tumor dose, the effect is backward. Effects on the body immune system after chemotherapy also large, physical condition has also been a great damage, so radiation treatment can't be with a larger field. Therefore, comprehensive treatment of the radiation should try to select the organ toxicity of chemotherapy drugs. Systemic reaction : Expressed as a range of disorders and disorders such as lack of energy, loss of appetite, body weakness, fatigue, nausea, vomiting, fullness after eating, etc., may do deal with a minor, should be promptly re-treated with Chinese medicine, improve the body's Immunity. Performance of dry skin pruritus, pigmentation and peeling can produce permanent light brown spots. The performance of the irradiated sites were moist skin eczema, blisters can cause severe erosion, rupture, partial rupture can be coated, such as the United States MEBO and suspended radiotherapy. Mucositis: Mild: the performance of the oral mucous membrane irritation, erythema, hyperemia, secretion decreased. Moderate: significant oropharyngeal edema, punctate albuginea, ulcer formation, with significant pain, difficulty eating. Severe: oral extreme congestion, erosion, bleeding, blending into the albuginea, ulcers increased, and a purulent discharge, pain, no eating.
Radiotherapy is one of best therapies for treating cancers .For many advantages and developed technologies, many types of cancers can be treated by radiotherapy such as lung cancer, oral cancer and breast cancer which are introduced. And by many researches and clinical applications, it can be told that radiotherapy has effective treatment for many cancers. But radiotherapy also has many disadvantages, and the largest one is its severe complications when it is used on patients in a long time. So when it's used in clinical applications, patients' conditions must be considered and controlled by surgeries. In the future, radiotherapy must be applied into more types of cancers and complications should be reduced as much as possible.