Tissue response after split treatment: the most common biological phenomenon affecting the response to split treatment is the repair ability of sublethal damage, different tissues have different repair ability of sublethal damage, late response tissues always have stronger repair ability than early response tissues, the result is that with the increase of split dose, the damage to late response tissues is greater than early response tissues, therefore, except for tumors with slow proliferation, splitting with smaller dose is likely to improve the treatment gain ratio and is more beneficial to protect late response tissues. Therefore, except for slow proliferating tumors, segmentation with smaller doses may improve the therapeutic gain ratio and is more beneficial to protect late responding tissues, while segmentation with larger doses is beneficial to improve the therapeutic ratio only on the basis of ensuring complete repair of sublethal damage to late responding tissues.
The redistribution of cell proliferation cycle in tumor: radiotherapy kills the more sensitive cell population, while the non-synchronous cell population becomes synchronized radioresistant cell population, after radiotherapy the non-synchronous cell population rapidly moves to the unsynchronized mixed cell population and plays its own sensitizing role. Repopulation: At a certain therapeutic dose, a relatively short course of treatment can increase the local control rate of tumors while decreasing the recurrence rate of tumors, which is especially prominent in fast-growing tumors. Reoxygenation: When the tumor volume is small, there are no oxygen-depleted cells. As the tumor volume increases, generally 20% of the stem cells remain in a constant ratio of oxygen depletion. After the oxygen-rich cells are killed by radiation therapy, the ratio of oxygen-depleted cells increases, and the oxygen-depleted cells are reoxygenated by migrating activities and improving oxygen supply, so that the treatment ratio of tumor increases accordingly. In fractionated radiation therapy, repair of sublethal damage and cell repopulation reduce the radiation effect of the total radiation dose. In experimental studies, it was found that the repair of damage was more important than fine repopulation. In high-dose fractionation therapy, the repair of damage becomes a major influence on the effectiveness of radiation therapy because the amount of cell proliferation is limited. It has been studied that the radiation dose required to produce the same skin response increases exponentially as the fractionated dose decreases and the total treatment time increases. Changes in radiation effects in tumor tissue, early response tissue and late response tissue due to changes in fractionation: acute response is closely related to cumulative dose (weekly dose), late damage is more sensitive to the size of fractionated dose, while the radiation response pattern of tumor tissue is similar to that of early response tissue, and the size of fractionated dose has a great influence on radiation damage to both normal tissue and tumor.?
Since the beginning of the 20th century, radiation therapy has been applied, and in the 1930s, a conventional fractionated radiation therapy program was formed, which refers to the radiation therapy method of irradiating once a day with 1.8~2.0Gy each time, 5 days a week. This method comes from long-term clinical experience, has been used for nearly a century, and has been clinically proven effective. With the emergence of the concept of stereotactic radiosurgery and the clinical application of various stereotactic treatment systems, the emergence of superconventional segmentation radiotherapy, a radiotherapy technique between conventional radiotherapy and radiosurgery, is considered to be the development trend of radiotherapy today. Ultra-conventional segmentation in body gamma knife treatment is mainly in the form of high-dose super-segmentation, the commonly used segmentation methods are: (1) less fractionation, high-dose segmentation: each time 8 ~ 18Gy dose, a total of 2 ~ 5 times treatment irradiation, 2 ~ 3 times a week, in 1 ~ 2 weeks to complete the entire treatment process. It is suitable for far away from sensitive organs, small tumor size, and the general condition of the patient is good. (2) Medium times, medium dose split: 5 to 10Gy each time, 5 to 10 times in total, 3 to 4 times a week or every other day, treatment is completed in 1 to 2 weeks. Suitable for general tumor gamma knife treatment, tumor volume is not greater than 5.0 cm, the patient’s general condition is good. (3) Multifractionation and small dose splitting: Using a dose close to that of conventional radiation therapy, 3-8 Gy or less each time, treating 3 times to 8 times per week, 1 time per day or 2 times per day, treating 5 times to 20 times in total and completing the whole treatment process in 2-3 weeks. It is suitable for patients who are adjacent to sensitive organs, with large tumor size and poor general condition.