Radiotherapy is an emerging science that has developed in this century. After the Second World War, due to the improvement of instruments and the accumulation of experience, the efficacy of radiotherapy has been significantly improved. Especially in the past 20 years, with the development of modern high technology and the popularization of precision instruments, radiotherapy has been developed rapidly and has become one of the main means of treating malignant tumors, about 70% of malignant tumors need radiotherapy (including comprehensive treatment and palliative treatment), radiotherapy plays an important role in the process of tumor treatment and its efficacy has been confirmed by clinical practice. While radiotherapy is developing, we should see its problems and shortcomings. How to improve the therapeutic effect on local tumor tissues while protecting normal tissues as much as possible has become an urgent problem in tumor treatment. Radiotherapy is a local treatment, about 1/3 patients do not get local control or local recurrence after radiotherapy, resulting in failure, and the conventional segmentation treatment methods commonly used at present do not show more superiority in long-term efficacy. It is important to select the best time for irradiation according to the metabolism and growth cycle of tumor cells in order to receive maximum efficacy. There are many types of tumors, different tumors have different biological behaviors, and the performance and prognosis of the same tumor vary from patient to patient. The effectiveness of radiotherapy is largely influenced by the sensitivity of tumors to radiation, which in turn depends on their tissue origin, degree of differentiation, pathological type and biological behavior of tumor cells. Therefore, in order to achieve the best clinical treatment effect, it is necessary to discuss the above issues from the perspective of molecular biology, hoping to provide a strong theoretical basis for radiation therapy for tumors.
I. Development of tumor radiation therapy
With the development of molecular biology, radiation therapy of tumor is also improving.
1.Fractional irradiation scheme, using hyper-segmentation (HF) or incremental radiation therapy (ESR). when HF is 7 weeks, the total dose increase effect is better, because the fractional dose is small and the late response is still the same as when using conventional treatment.
2. Clinical application of high LET radiation: ① negative π meson therapy; ② heavy ion therapy: better effect than conventional treatment of LET; ③ neutron therapy has better effect on advanced or poorly differentiated tumors; ④ boron neutron capture therapy (BNCT), superior to treatment of intracerebral tumors such as highly differentiated glioma.
3.Heating therapy or thermal therapy: thermal therapy sensitizes cellular radiation, and the mechanism of action is: heating therapy can selectively and preferentially inhibit the repair of damage with active genes; when irradiation is combined with heating, the half-repair time of DNA double-strand breaks is prolonged, and the efficacy can be increased with the simultaneous application of low-dose rate irradiation and heating.
4, the application of photodynamics in radiation therapy: with the development of photons will appear higher wavelength, higher absorption coefficient, penetrate deeper and better sensitizers to improve the effect of radiotherapy.
At present, clinical workers have proposed three-dimensional radiotherapy measures, also known as three-dimensional conformal radiotherapy (3-DCRT), which is a method to make the shape of the dose distribution in the high-dose area consistent with the actual shape of the tumor in the target area in three-dimensional direction, which can make the target area reach the highest dose according to the shape of the tumor, and the dose distribution is uniform and the normal tissues suffer less, thus improving the tumor control rate, reducing the normal tissue complications and It is an advanced technology of radiation therapy to improve local tumor control, reduce the distant metastasis rate of certain tumors, and improve the survival rate of tumor patients. In conclusion, with the development of molecular biology, it is believed that it will open up a new and broader prospect for radiation therapy of tumor.
Radiation therapy for gastric cancer
Gastric adenocarcinoma has low radiosensitivity, and only 60% of the tumors shrink by more than 50% after radiotherapy alone or combined with chemotherapy, and only 10% of the tumors disappear completely. The gastric wall and mucosa are sensitive to radiation, and mucosal ulcers can be produced in 5~8 weeks after irradiation at a dose of 000 cGy at home, which can occasionally cause perforation. The organs around the stomach, such as liver, small intestine, kidney and spinal cord, also have a certain limit of radiation tolerance. Wieland and Hymmen et al. reported that the 5-year survival rate of radical dose radiotherapy for gastric adenocarcinoma was only 7%. The role of radiotherapy in the treatment of gastric cancer is mainly adjuvant or palliative.
1.Indications for radiotherapy
There are four main forms of radiotherapy for gastric cancer: preoperative radiotherapy, intraoperative radiotherapy, postoperative radiotherapy and palliative radiotherapy: ① Preoperative radiotherapy: preoperative radiotherapy should be performed for middle and advanced gastric cancer, ulcerated type or hard cancer located in the pylorus and gastric body, with maximum diameter less than 6 cm, in good general condition and feasible for surgical exploration. ②Intraoperative radiotherapy: it is applicable to patients with late stage II, stage III and limited stage IV (pancreatic or transverse colon involvement) that can be surgically resected. ③Postoperative radiotherapy: the tumor has been basically resected, but there are residual subclinical lesions or microscopic lesions that can be treated with postoperative radiotherapy. ④Palliative radiotherapy: for patients with advanced localization and inoperable resection, as long as the general condition can tolerate radiotherapy, palliative radiotherapy is feasible to relieve the symptoms of obstruction. In the past, palliative radiotherapy has good hemostatic effect on bleeding caused by tumor rupture. In recent years, due to the popularization of interventional radiology, selective arterial embolization has been used to stop bleeding with better effect.
2.Technology of radiotherapy
External irradiation: Before radiotherapy, it should be positioned by simulator according to the information of gastroscopy, X-ray angiography, surgical exploration and intraoperative retained markers. The preoperative radiotherapy irradiation field should include 2~3 cm outside the primary focus and the lymph nodes within the omentum of the large and small curves of the stomach and the pyloric lymph nodes. Postoperative radiotherapy should include the remnant stomach, anastomosis, duodenal remnant, tumor bed and the main lymphatic drainage area. For palliative radiotherapy of locally advanced gastric cancer, the scope of irradiation varies according to the disease and mainly includes the gastric tumor. External radiation is administered in two fields, anterior and posterior, and care should be taken to protect the liver and kidney. The radiation source should be high-energy X-ray or 60Coγ. Irradiation is given once a day at a dose of 180 cGy, five times a week. The total amount of preoperative radiotherapy should be 3000cGy~4000cGy/3~4 weeks, and surgery after 2 weeks of rest; single high dose irradiation of 1000cGy~1500cGy/1 time is also reported in the literature. The total amount of postoperative radiotherapy or palliative radiotherapy is in the range of 4500cGy~5000cGy/5~5.5 weeks; the field should be reduced after irradiation to 4500cGy. Treatment with super-segmentation method, irradiation twice a day, each time with 4~6 hours interval, each dose 150cGy~165cGy, total amount up to 4050cGy/27 times~4500cGy/27 times.
②Postoperative radiotherapy: irradiation was performed after major gastric resection and before gastrointestinal anastomosis. The scope of irradiation includes the tumor bed and the most easily invaded lymph nodes such as the left gastric artery, the common hepatic artery, the splenic hilum and around the abdominal aorta, and part of the pancreas. Depending on the stage of the disease, the location of the tumor and the extent of its infiltration, the appropriate light-limiting cylinder and the energy of the electron beam should be selected. Care should be taken to protect the surrounding normal organs when irradiating. The single dose is 2800cGy~4000cGy.
3.Efficacy of treatment
The literature reports that preoperative radiotherapy can increase the resection rate of radical surgery by about 20% and the 5-year survival rate of intermediate to advanced gastric cancer by 10%-25%. Liu Changfa et al. reported that the radical surgical resection rate of gastric cancer increased by 10% after preoperative radiotherapy; the survival rate also improved, and the 5-year survival rate was 51.8% (29/56) in the preoperative radiotherapy group and 27.4% (12/62) in the surgery-only group; among them, those with clinical stage III, tumor less than 6 cm, pathological classification of low-differentiated adenocarcinoma, and lesions invading the muscular layer had good results; Tankahashi et al. reported that they could not The one-year survival rate of those who could not be surgically resected or treated with radiotherapy after palliative resection was 74%, and the 2.5-year survival rate was 27%. Gao Rugui et al. reported 26 cases of advanced gastric cancer or postoperative recurrence in 7 units in China with individual radiotherapy doses above 4000 cGy, and the effective rate reached 69.2%, with 6 cases of tumor disappearance; only 1 case survived for 2 years, and the average survival period of those who died was 8 months. Holbrook et al. reported that the mean survival period after radiotherapy was 13 months and the 5-year survival rate was 12% for those who added 5-fluorouracil on the first to third day of radiotherapy, and 5.9 months and 0% for those who received radiotherapy alone. Survival rates were 88.1%, 77.0%, 44.6% and 19.5% for the stage I, II, III and IV intraoperative radiotherapy groups and 93%, 54.5%, 36.8% and 0% for the surgery alone group. He concluded that intraoperative radiotherapy was ineffective for stage I lesions, and that intraoperative radiotherapy for stage II, III and IV patients could improve survival. Chen Guoxiong et al. reported that the 3-year survival rate of intraoperative radiotherapy for stage III patients was 39%, compared with 26% for the surgical group; 16 patients who had intraoperative radiotherapy for unresected tumors died within six months, which failed to extend the survival period compared with the surgical exploration group.
4.Reaction to radiotherapy
The acute reactions of external irradiation are mainly loss of appetite and nausea. The reactions of patients who have undergone partial gastrectomy or subtotal gastrectomy are less severe than those who have not undergone gastrectomy. During radiotherapy, attention should be paid to the observation of weight change and the strengthening of supportive therapy. Complications of intraoperative radiotherapy include temporary elevation of blood starch and blood glucose, and other complications include gastric perforation, small intestine ulcer, anastomotic fistula, etc. The complications can be reduced if the intraoperative operation is carefully performed, the appropriate size of the limiting cylinder is strictly selected, and attention is paid to protecting part of the pancreas.
III. Prognosis of gastric cancer
Gastric cancer is one of the most common malignant tumors of the digestive tract in China. 1981, the National Gastric Cancer Collaborative Group retrospectively summarized 11,734 cases of gastric cancer in 27 units after 5 years of surgery, of which 9,602 cases were treated with various surgeries. Among them, 2701 cases (23.0%) had radical resection with an operative mortality rate of 2.5% and a 5-year survival rate of 31.2%; 3128 cases (26.7%) had palliative resection with an operative mortality rate of 3.9%. The 5-year survival rate after surgery was 11.7%; non-resectional surgery was performed in 3773 cases (26.7%), with a surgical mortality rate of 7.6%. Among them, 1831 cases (15.6%) were operated by shortcut anastomosis, with an operative mortality rate of 5.5% and a median survival time of 5.5 months; 1415 cases (12.0%) were operated by simple open exploration; with an operative mortality rate of 9.1% and a median survival time of 4.7 months.