1. What is radiation therapy?
In short, it is a method of treating disease with radiation. Radiation therapy of tumor is a method of using X-rays or other rays to irradiate tumor so as to destroy tumor cells and achieve the purpose of treatment. Radiation therapy is one of the most important treatment means in the treatment of malignant tumor, and 75% of tumor patients may need radiation therapy at different stages, so it is a very important treatment means and also a widely used treatment method.
Features: great effect on naive and vigorously growing tumor cells.
Disadvantage: while radiation destroys and kills tumor cells, it also has a destructive effect on surrounding normal tissue cells.
2.Classification of radiation therapy and examples
(1) In terms of radiation used in radiotherapy, it can be divided into 3 categories.
① α, β and γ rays emitted by radioisotopes, such as I131 treatment, γ-knife treatment of Co60.
② X-rays produced by accelerators, currently X-rays treatment is most commonly used in the clinic, also including X-knife treatment (scientific name for stereotactic radiation therapy, that is, the use of X-rays, multiple small field three-dimensional cluster single high-dose directional irradiation, the surrounding normal tissue dose is very small, the rays on the lesion to play a role similar to a scalpel, so the name X-knife. γ-knife naming is similar, except that the rays are γ-rays); conventional X-ray treatment is most commonly used. X-knife or γ-knife requires certain indications.
(3) Accelerator-generated electron beam, proton beam, neutron beam, and other heavy particle beams, etc., of which electron beam is more commonly used in the treatment of superficial lesions, and the use of other ray beams is relatively rare at present.
(2) In terms of radiation modality, there are 2 types.
① External irradiation (long-distance irradiation): the radiation source is located outside the body at a certain distance, concentrating on a certain part of the body, currently commonly used;
② Internal irradiation (brachytherapy): The radiation source is sealed and placed directly into the treated tissue or the natural cavity of the body for irradiation, such as particle implantation for prostate cancer. Certain indications are required.
(3) In terms of radiotherapy techniques can be divided into.
Conventional radiotherapy, 3D conformal radiotherapy, 3D intensity modulated radiotherapy, etc. The latter two are becoming more and more popular and have become the mainstream treatment techniques.
3.Which rectal cancer patients need radiation therapy?
(1) Preoperative radiotherapy for patients with stage II/III rectal cancer.
(2) Postoperative radiotherapy for patients with stage II/III rectal cancer.
(3) radiotherapy for patients with T4 or locally advanced inoperable rectal cancer
(4) Radiotherapy for pelvic recurrence of rectal cancer after.
(1) Anastomotic recurrence: postoperative anastomotic recurrence, if inoperable and no previous pelvic radiotherapy has been performed, radiotherapy can be considered;
② Recurrence at other sites: radiotherapy can be used as one of the treatment means, together with surgery and chemotherapy.
4.What cases are not suitable for radiotherapy?
For patients with intestinal perforation, cachexia and extensive metastasis, radiotherapy should not be performed, and it is better to discuss with radiotherapists to determine the specific situation.
5.Timing of radiotherapy and surgery for rectal cancer
(1) Time interval between preoperative radiotherapy and surgery
The time interval between radiotherapy and surgery should be reasonable. For preoperative radiotherapy, the pelvic cavity is congested and edematous after radiotherapy, so premature surgery may increase the complications of surgery, but if the time is delayed too long, fibrosis in the radiation area may increase the difficulty of surgery. Currently, the time interval between preoperative radiotherapy and surgery in most foreign studies is 4-8 weeks.
It is recommended to review 4-6 weeks after the end of radiotherapy for efficacy assessment, and to perform surgery at 6-8 weeks.
(2) Time interval between postoperative radiotherapy and surgery
Patients with indications for postoperative radiotherapy (those with pathological diagnosis of stage II/III) are recommended to start radiotherapy early after recovery from surgery, generally speaking, treatment can be started after stool formation and regularity (about 4-8 weeks after surgery); chemotherapy + radiotherapy + chemotherapy can also be received, but for patients who have undergone combined abdominoperineal resection (permanent fistula), early radiotherapy (starting radiotherapy immediately after recovery from surgery) is significantly However, for patients who underwent combined abdominoperineal resection (permanent fistula), early radiotherapy (radiotherapy immediately after recovery from surgery) is significantly better than late radiotherapy (those who received all chemotherapy after surgery and then radiotherapy).
6.Staging before radiotherapy
Staging examination is used to guide the selection of the first treatment decision, therefore, tumor patients need to improve the staging examination before radiotherapy. The following are included
(1) Medical history inquiry, including family history.
(2) Physical examination: including rectal examination and general examination.
(3) Colonoscopy and biopsy: full colonoscopy is recommended to understand the accompanying tumors and other colorectal lesions, and biopsy can be performed to clarify the masses found, and the pathological results are the main basis for the diagnosis of rectal cancer.
(4) Colon air-barium double imaging: it is the preferred method to diagnose rectal cancer, which can observe the size, location, morphology and type of lesions, and can detect multiple lesions in the colon.
(5) Pelvic CT, MRI and ultrasound endoscopy: CT can understand the location, size, morphology, relationship with surrounding tissues and lymph node metastasis of lesions, while CT can also exclude whether there are metastases in liver and lung; compared with CT, rectal MRI can more clearly reflect the relationship between rectal lesions and surrounding tissues, and can provide more definite staging hints. In addition, rectal ultrasound endoscopy can help determine the depth of lesion invasion and lymph node metastasis, which is similar to the role of rectal MRI.
(6) CT of the abdomen: to understand whether there are metastases in the liver, retroperitoneum, and abdominal cavity.
(7) Chest X-ray or CT: to understand whether there are lung metastases.
(8) Laboratory tests: including routine blood, liver and kidney function assessment, tumor markers, stool routine, etc.
At present, ultrasound endoscopy, rectal or pelvic MRI and thoracoabdominopelvic CT are recommended as the evaluation means of preoperative staging of rectal cancer, while PET or PET/CT is not recommended as staging examination for the time being.
7.Specific process of radiotherapy
In short, the process of receiving radiotherapy includes 4 steps
(1) Positioning (mainly refers to CT positioning).
Determine the treatment body position, fixation and CT simulator under scanning.
The purpose of position determination: position determination refers to the decision of the posture to be taken during radiotherapy, which is beneficial to the plan design and position repetition to reduce adverse reactions, and the requirements of radiotherapy position are different for different sites.
The purpose of fixation (including fixation of fixators and molds): it facilitates the repetition of the same body position to the maximum extent for each treatment and reduces the positional error during treatment.
Under-simulator scanning: including CT under-simulator scanning and conventional under-simulator scanning. Purpose: to obtain image information of treatment-related parts and to determine the radiotherapy area and the area to be protected.
(2) Target area outlining.
The area to be treated and the surrounding normal tissues and organs are outlined on the patient’s image (most of the current designated CT images), and the treatment area usually includes the tumor and its surrounding areas that may have tumor infiltration. The target area outline is crucial for radiotherapy, and the physician will invest a lot of effort in this part, so it takes more time.
(3) Plan design and review.
The physicist uses the computer to design the radiotherapy plan according to the physician’s target area outline, treatment dose and vital organ restrictions: from which angles to give radiation treatment, the size of the treatment area, dose, etc., and calculates a synthetic dose distribution map (similar to the elevation plan in a map) to reflect the dose distribution in the target area and the exposure of normal tissues and organs.
The physician and the physicist review the plan together and continue to revise and improve it if it does not meet the requirements, and implement the radiotherapy plan if it does. This phase requires close cooperation between the physician and the physiatrist, and the modification process varies depending on the complexity of the treatment plan, sometimes it takes 1-2 days to complete a satisfactory plan, and sometimes it takes 5-7 days or longer.
(4) Plan implementation.
Once both the physician and the physiatrist are satisfied with the treatment plan, the treatment can be implemented. The first treatment is performed after the first treatment is posed and photographed correctly. Subsequent periodic radiographs are taken to verify that the change in treatment range is within the error tolerance for each treatment.
In conclusion, the current 3D conformal radiotherapy and 3D intensity-modulated radiotherapy under CT guidance require a very high degree of precision in treatment. Patients receive a more definite and precise range and dose of radiotherapy, while protecting the surrounding normal organs or tissues to the maximum extent.