1. What is radiotherapy?
Radiotherapy, abbreviated as RT, is one of the main means of treating tumors. It uses radiation to kill cancer cells, causing the tumor to shrink or disappear. Radiation damages the cells in the irradiated area (target area), causing these cells to stop dividing until they die. The goal of radiotherapy is to kill tumor cells to the greatest extent possible while protecting normal tissues.

2. Which tumors require radiotherapy?
Current statistics show that approximately 70% of patients with malignant tumors need radiotherapy for control at different stages of the disease progression. However, for a specific patient, whether to use radiotherapy should be determined according to the standardized treatment principles of the tumor, the stage of tumor development, and the patient's physical condition. Tumors that are clinically suitable for radiotherapy mainly include: nasopharyngeal carcinoma, laryngeal cancer, tonsillar cancer, tongue cancer, malignant lymphoma, cervical cancer, skin cancer, brain tumor, esophageal cancer, breast cancer, lung cancer, rectal cancer, bone tumor, liver cancer, soft tissue sarcoma, etc.

3. How long does radiotherapy take?
According to the nature of the tumor and the treatment purpose, radiotherapy is divided into radical radiotherapy, preoperative radiotherapy, postoperative radiotherapy, and palliative radiotherapy. The time required to complete radiotherapy varies depending on different treatment purposes. The following is a detailed description:
- Radical radiotherapy: Using radiotherapy alone to control or even cure the tumor. Some tumors, such as nasopharyngeal carcinoma, laryngeal cancer, tonsillar cancer, tongue cancer, malignant lymphoma, cervical cancer, skin cancer, etc., can be cured by radiotherapy alone. In addition, for tumors located in areas where surgery is not possible or for patients who do not want surgery, radical radiotherapy can be given alone. In radical radiotherapy, the radiation dose must be sufficient; otherwise, there will be a hidden danger of recurrence. It generally takes 6 to 7 weeks to complete.

- Preoperative radiotherapy: When the tumor is too large or adheres to surrounding organs, making surgery impossible, a certain dose of radiotherapy is given before surgery to shrink the tumor and facilitate the operation. It generally takes 3 to 4 weeks to complete, and the patient should rest for 3 to 6 weeks before surgery. This rest period after radiotherapy is for the normal tissues to repair the radiation reactions, and at the same time, it allows the tumor to further regress for easier surgical resection. During the radiotherapy and rest periods, cancer cells are gradually dying, so there is no need to worry that the cancer cells will grow due to the postponed surgery.

- Postoperative radiotherapy: Since the tumor is located in a special area or adheres to surrounding organs and cannot be completely removed, these residual tumors will relapse and metastasize after surgery. Therefore, radiotherapy should be given after surgery to eliminate the remaining cancer cells. The radiotherapy time depends on the amount of residual tumor. If there is a large amount of residual tumor and it can be seen with the naked eye, it almost requires the same time and dose as radical radiotherapy. If there is a small amount of residual tumor and cancer cells can only be seen under the microscope, generally, about two-thirds of the radical radiotherapy dose is sufficient, that is, it takes 4 to 5 weeks.

- Palliative radiotherapy: When the growth of the tumor causes pain to the patient, such as pain from bone metastases, difficulty breathing caused by the tumor blocking or compressing the trachea, swelling caused by the compression of veins leading to blood return obstruction, headache caused by brain metastases, and the risk of paralysis caused by the tumor invading and compressing the spinal cord, a certain dose of radiotherapy is given to relieve symptoms and reduce pain. The radiation dose varies according to the location of the tumor and the purpose of treatment, ranging from several radiotherapy sessions to one month.

4. What is external beam radiotherapy and what is internal radiotherapy?
According to the distance of the radiation source, it is divided into external radiation and internal radiation:
- External beam radiotherapy: Also known as teletherapy, the radiation is emitted from a machine at a certain distance outside the human body (for example, 75 cm for a cobalt-60 machine and 100 cm for a linear accelerator) to irradiate the tumor. This kind of radiation has high energy and strong penetrating power, and the tumor can receive a relatively uniform radiation dose. External beam radiotherapy is a commonly used method in radiotherapy at present.

- Internal radiotherapy: Also known as brachytherapy, the radiation source is directly placed inside the tumor (particle implantation) or in the lumen adjacent to the tumor (such as the trachea, esophagus, vagina, etc.) for radiotherapy. The radiation source used in internal radiotherapy has a short radiation range and low penetrating power. The advantage is that the tumor can receive a higher dose, and the distant normal tissues receive a lower dose and are thus protected. The disadvantage is that the dose distribution is uneven, which is likely to cause hot spots (areas with excessively high doses) and cold spots (areas with excessively low doses), increasing the risk of tumor residue and recurrence. Therefore, except for cervical cancer, currently internal radiotherapy is only used as a supplementary dose to external beam radiotherapy and is not used alone.

5. What is conventional radiotherapy? What is stereotactic radiotherapy?
- Conventional radiotherapy is a commonly used traditional radiotherapy method. The irradiation range includes the tumor, nearby metastatic lesions, and the area where metastasis is likely to occur. Generally, it is irradiated once a day, five times a week, and a conventional radiation dose is given each time. The advantage is that both the tumor and the nearby lymph node area can be irradiated, and the cost is low. The disadvantage is that the surrounding normal tissues receive unnecessary irradiation, resulting in radiotherapy side effects.

- Stereotactic radiotherapy, also known as gamma knife or X-knife that we often hear about, is a method in which radiation focuses on the tumor lesion from multiple different directions. While destroying the tumor, it can better protect the surrounding normal tissues. The treatment result is that the tumor necroses and disappears just like being cut by a knife, so it is vividly compared to a "knife". The gamma knife (X-knife) is not a surgical operation!

6. What is the difference between the gamma knife and the X-knife?
Commonly used radiation rays in radiotherapy include gamma rays, X-rays, beta rays, etc. Gamma rays are generated during the spontaneous decay of radioactive elements such as cobalt-60 (or other radioactive elements); X-rays are generated by an accelerator (high-speed electrons hitting a tungsten target). Therefore, stereotactic radiotherapy using cobalt-60 as the radiation source is called the gamma knife, and stereotactic radiotherapy using an accelerator as the radiation source is commonly known as the X-knife.

- The head gamma knife has multiple cobalt-60 radiation sources arranged in a hemispherical device, and the radiation rays focus on the intracranial lesion through a helmet with multiple apertures (collimator). Due to the influence and limitation of many factors, the largest aperture of the helmet can only reach 18 mm. The gamma knife uses invasive fixation (fixing the head frame to the skull with rivets) and is generally performed only once, so it is suitable for intracranial lesions of less than 18 mm.

- The largest collimator of the X-knife can reach 50 mm. When treating intracranial lesions, non-invasive fixation technology is used (a kind of thermoplastic mask that softens in hot water, is then placed on the patient's face, adjusted to fit the patient's face shape, and hardens after cooling for fixation). Therefore, it is conducive to fractionated treatment, suitable for lesions of various sizes, and has more advantages for slightly larger lesions. (Note: Collimator: In order to achieve a certain purpose, the radiation rays coming out of the machine need to be directed and limited. The device that plays this role is called a collimator).

7. Is there radioactivity in the human body after radiotherapy?
Many patients are worried about whether there is radioactivity in their bodies after radiotherapy. To answer this question, it depends on the radiotherapy method used.
Generally, there is definitely no radioactivity in the human body after external beam radiotherapy because the radiation source is in a machine at a certain distance outside the body. So after radiotherapy, patients can be closely with their relatives and friends.

In internal radiotherapy, the radiation source is placed in the body, and the organs near the radiation source are radioactive, so attention should be paid to protecting the surrounding people.

Systemic radiotherapy is to inject radioactive elements into the blood vessels (such as using the radioactive element strontium to treat multiple bone metastases). These radioactive elements reach the tumor and other parts of the body with the blood flow. As the human body metabolizes, they will also be excreted into secretions such as saliva and urine. Therefore, in a certain period of time, it is necessary to protect the surrounding people and properly handle the excreta.

8. Other radiotherapy methods that are currently in use or under development
- Three-dimensional conformal radiotherapy (3DRT): Traditional conventional radiotherapy is two-dimensional (length and width of the tumor) radiotherapy. If CT, PET, or magnetic resonance imaging (MRI) is used to modify the radiation rays according to the irregular shape of the tumor in three dimensions (length, width, and depth) for radiotherapy, it is called three-dimensional conformal radiotherapy. The advantage is that it can protect the surrounding normal tissues.

- Intensity-modulated conformal radiotherapy (IMRT): Based on three-dimensional conformal radiotherapy, the radiation dose is adjusted through a certain method to achieve a uniform radiation dose within the tumor.

- Image-guided radiotherapy (IGRT): During the implementation of radiotherapy, the planned tumor site is accurately positioned through CT image guidance, further improving the accuracy of tumor treatment.

- Biology-guided radiotherapy (BGRT): There is a certain degree of heterogeneity among tumor cells in the tumor tissue, and tumor cells also have different sensitivities to radiation. Different radiation doses are selected according to the biological characteristics of different tumor cells to achieve the ultimate goal of completely killing the tumor. This radiotherapy method is currently under development.

9. How long does it take for radiotherapy to take effect?
The effect of radiotherapy cannot be immediately apparent after radiotherapy. Tumor cells begin to die a few days or weeks after radiotherapy, and the necrosis of tumor cells will continue for several weeks or months after the end of radiotherapy.

10. Is radiotherapy painful? What are the side effects of radiotherapy?
Radiotherapy uses radiation to kill tumors. This high-energy radiation is invisible to the naked eye. While killing tumor cells, the radiation also damages the normal cells within the irradiated range. The radiation damage to normal tissues will gradually recover after the end of radiotherapy. At the beginning of radiotherapy, patients will not experience the pain caused by radiotherapy. However, as radiotherapy continues, the degree of cancer cell necrosis gradually increases, and the degree of damage to normal tissue cells will also increase. At this time, there will be corresponding manifestations of damage to normal tissues, which is called the acute reaction of radiotherapy (for example, radiation esophagitis, and patients will feel pain in the esophagus when swallowing, etc.). Doctors will deal with these side effects of radiotherapy. One should not give up the opportunity of tumor treatment because of these temporary radiotherapy reactions.