Unveiling the mystery of open therapy

Author: Yang Xiaojing, Shanghai Sixth People's Hospital

Reviewer: Fu Jie, Chief Physician, Shanghai Sixth People's Hospital

In the basement or relatively hidden area of ​​a hospital building, there is a department that is often shrouded in a "mystery" veil - the radiotherapy department. Today, we will unveil its true face for you.

The reason why the radiotherapy department seems "mysterious" is mainly because relatively few medical staff and patients have contact with and understand this department. The radiotherapy department, whose full name is radiotherapy department or tumor radiotherapy department, is a treatment-oriented department, mainly serving tumor patients, and also includes a small number of patients with benign diseases. Its treatment method is to use radiation to kill tumor cells, and its main equipment includes linear accelerators and close-range afterloading treatment machines. It is the word "rays" that makes many people stay away from the radiotherapy department.

So, how are these rays produced?

The linear accelerator is the core equipment in tumor radiotherapy, which can generate high-energy rays, including electron beams and X-rays. The electrons emitted by the electron gun of the linear accelerator gain huge kinetic energy after being accelerated by the accelerator tube. When these high-speed electrons bombard the metal target, high-energy X-rays will be generated; if the electrons are directly extracted without hitting the target, high-energy electron beams will be formed. These high-energy rays are only generated when the accelerator is turned on and in the treatment state, and no rays are generated when it is turned off. In order to meet the protection requirements, the accelerator is usually installed in the basement and is protected by a shielding wall made of concrete on all sides. For high-energy linear accelerators, the thickness of the main shielding wall is generally up to 240cm. Therefore, there is no need to worry about being exposed to radiation when passing near the accelerator room of the radiotherapy department, because the thick protective wall has completely blocked the radiation.

Who needs radiotherapy?

About 70% of cancer patients need radiotherapy during treatment. Common diseases include breast cancer, lung cancer, esophageal cancer, rectal cancer, cervical cancer, prostate cancer, etc. Radiotherapy can be divided into external radiotherapy and internal radiotherapy according to the treatment method. External radiotherapy is what we usually call external irradiation. The patient lies on the accelerator treatment bed, and the rays generated by the accelerator penetrate the skin and tissue to reach the tumor site in the body that needs treatment. Internal radiotherapy, also known as close-range radiotherapy or afterloading radiotherapy, uses the natural cavity of the human body (such as the vagina, etc.) or the interstitial space of the tissue to place the applicator into the cavity or tissue that needs radiotherapy, and then the radiation source reaches the tumor site through the applicator for radiotherapy. In addition to malignant tumors, some benign diseases such as keloids, pigmented villonodular synovitis, heterotopic ossification, etc. also require radiotherapy to prevent recurrence.

How do radiation kill tumor cells?

Is there any harm to normal tissue? Our body cells can be damaged or killed by radiation. Since tumor cells divide faster than normal cells and repair slower than normal cells, they are more sensitive to radiation. Radiotherapy uses this principle to kill or destroy tumor cells that cannot be repaired. Modern radiotherapy technology has developed into precision radiotherapy. With the assistance of advanced imaging and computer technology, doctors and physicists can use computer simulation software to develop personalized radiotherapy treatment plans for patients to ensure that the radiation is accurately "directed to where it hits". These plans take into account the location, size and shape of the tumor, while also fully considering the radiation dose to the surrounding normal tissues and organs. An excellent radiotherapy plan can minimize damage to surrounding tissues while ensuring the therapeutic effect on the tumor.

What steps are involved in the radiation therapy process?

Some patients may worry about why they have not been scheduled for radiotherapy after coming to the radiotherapy department for many days. Before radiotherapy is implemented, radiotherapy doctors, physicists and technicians need to do a lot of preparation. First, the doctor determines when the patient needs radiotherapy. For example, patients with gynecological tumors generally start radiotherapy about 4 weeks after surgery, and patients with head and neck tumors receive radiotherapy about 6 weeks after surgery. After confirming that radiotherapy is needed, the patient needs to go to the first station for body film making. In order to achieve precise radiotherapy effects, the displacement error of the treatment must be controlled within 3mm. According to the patient's treatment site, an individualized model is developed to ensure the repeatability and accuracy of the patient's position. Currently, commonly used model materials include thermoplastic film, foam glue, vacuum pad, etc. It takes about half an hour to make the model. The second station is a simulated CT scan. The patient needs to carry out a simulated CT scan of the relevant parts with the prepared body film according to the doctor's instructions (such as whether to hold urine, whether to fast, etc.). This process takes about half an hour. The obtained CT image is transmitted to the radiotherapy planning system by the technician. The third station is for the radiation oncologist to refer to the patient's imaging examination and clinical examination, outline the target area and organs at risk that need to be treated layer by layer on the simulated CT, and determine the number and dose of radiotherapy. This process takes 1 to 3 days. The fourth station is for the physicist to design the radiotherapy plan on a dedicated workstation. After the plan design is completed, the plan needs to be verified, that is, before the patient receives radiotherapy, in order to reduce errors and ensure that the irradiated tumor is not off-target, the irradiation position and dose need to be verified. If the plan verification fails, the cause needs to be analyzed or even the radiotherapy plan needs to be redesigned. This process also takes 1 to 3 days. Although the last two stations do not require patient participation, patients need to wait patiently at home for 1 to 6 days. After the above steps are completed, the doctor will notify the patient to come to the hospital for repositioning, conversation and treatment. External irradiation is generally once a day and 5 times a week. The total number of radiotherapy depends on the condition. Generally, no secondary radiotherapy is performed on the same part within two years. The above is the external irradiation process.

Figure 1 Copyright image, no permission to reprint

Patients generally do not feel anything unusual during treatment, and the radiation is invisible to the naked eye. During each radiotherapy session of more than ten minutes, the patient is like lying down to rest for a while, and will not feel fever or burning. The process of internal irradiation is more complicated than that of external irradiation. The most common patients who receive internal irradiation are cervical cancer patients. Internal irradiation is usually performed 1 to 2 times a week, and local anesthesia is arranged before treatment according to the condition. Patients with cervical cancer are treated in the lithotomy position, and the doctor selects a suitable applicator based on the pre-treatment imaging data and physical examination. After the applicator is inserted, a CT scan is performed, and the CT images obtained are transmitted to the afterloading treatment planning system. The doctor outlines the target area and organs at risk with reference to the imaging data and the residual lesions, and the physicist then designs and implements the plan. After the radiotherapy is completed, the applicator is removed to check for bleeding and other conditions. The overall treatment time for one afterloading is between half an hour and one hour. All the above steps need to be repeated for each afterloading to achieve the purpose of accurate three-dimensional painless afterloading radiotherapy under image guidance.

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