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Precise radiotherapy, that is, three-dimensional conformal intensity modulated radiotherapy, refers to a tumor treatment method that combines radiotherapy medicine with computer network technology and physics. The entire radiotherapy process is controlled by computer.

Precision radiotherapy

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Precise radiotherapy, that is, three-dimensional conformal intensity modulated radiotherapy, refers to a tumor treatment method that combines radiotherapy medicine with computer network technology and physics. The entire radiotherapy process is controlled by computer.

The development of modern medicine has gradually made it possible for humans to control and conquer cancer. In the clinical treatment of tumors, surgery,

The differences from traditional radiotherapy techniques can be summarized as the "four most", that is, the maximum exposure dose in the target area (lesion area), the minimum normal tissue surrounding the target area, the dose distribution in the target area is the most uniform, and the target location and The most accurate irradiation, the advantages are "high precision, high dose, high curative effect, low damage", mainly including three-dimensional conformal radiotherapy and intensity-modulated conformal radiotherapy.

Precise radiotherapy is a new type of tumor radiotherapy technology based on conventional radiotherapy through precise tumor positioning, accurate plan design, dose calculation and precise execution on the treatment machine. It combines three-dimensional image processing technology and high-precision dose calculation. Algorithms, cutting-edge straight lines

The first is the positioning, because the tumor receptor position, breathing and other factors, the position is difficult to fix, ordinary

Thanks to the strong support of computer technology, radiophysics, radiobiology, molecular biology, imaging and functional imaging, and the organic combination of multi-disciplinary disciplines, radiotherapy technology has achieved revolutionary progress. According to WHO statistics at the end of 1998, 45% of cancer patients can be cured, of which 22% are cured by surgery, 18% are cured by radiation therapy, and 5% are cured by chemotherapy. Radiotherapy also has the advantage of preserving organ function and beauty. 3D stereotactic radiation therapy technology will further strengthen this advantage. In the past ten years, China's 3D stereotactic radiotherapy technology has developed extremely rapidly. From ordinary radiotherapy to 3D stereo high precision directional radiotherapy, a 3D stereotactic system has been used, with additional beam limiting devices and position fixing devices, to make the target area edge dose gradient. The steep decline makes a sharp "knife" cut between the tumor target area and the normal tissue at the edge. The purpose is to give high dose irradiation to the target area to protect normal tissues and important sensitive organs outside the target area from damage.

Three-dimensional conformal RT (3D-CRT)

The growth mode and location of tumors are complex. The radiation treatment radiation field should include all tumor tissues and lymph drainage areas, as well as a certain range of peripheral edges, also known as safe margins. In order to meet the requirements of the shape of the radiation volume and the target volume, while avoiding unnecessary irradiation of normal tissues, the shape of most irradiation fields is irregular. In the past clinical radiotherapy practice, low melting point lead blocks were generally used. The technology implements radiotherapy for irregular irradiation fields. In the 1940s, some people began to use the semi-automatic primitive multi-leaf grating (MLC) technology or low melting point lead block to guide the most primitive conformal radiotherapy under the guidance of the two-dimensional radiotherapy plan. This technology has been used clinically for half a century. Due to the advancement of computer technology, radiophysicists have replaced the hand-made lead stops with more advanced multi-leaf gratings to achieve the purpose of shaping the rays. The plasticity of multi-leaf gratings is controlled by a computer. Shape, change the orientation of the blade when the accelerator frame rotates, adjust the shape of the irradiation field, and make it completely automated. Take conformal radiotherapy technology to a new level. In recent years, computer processing of imaging diagnostic images has enabled three-dimensional reconstruction of the radiotherapy target area in the human body and adjacent important tissues and organs, thereby achieving clinically three-dimensional conformal radiotherapy under the guidance of a three-dimensional radiotherapy plan. At present, more and more hospitals and tumor treatment centers are being used in the clinical practice of radiation tumors, and they are gradually being incorporated into routine applications.

The positioning technology requirements for three-dimensional conformal radiotherapy for trunk tumors are more complicated. Compared with head and neck tumor radiotherapy technologies, the physical movement of the thorax and abdomen affects the accuracy of the three-dimensional reconstruction of the image and the radiotherapy plan. In addition, the trunk tumor has a large volume The treatment volume is also large; in addition, the shape of the radiotherapy target volume of the trunk tumor is generally irregular. Therefore, the requirements for three-dimensional conformal radiotherapy for trunk tumors are relatively high. ICRU50 report details the standardization of tumor volume, clinical target volume, planned target volume, and treatment prescription. Broadly speaking, based on the reconstruction of 3D images, the radiation dose volume and the shape of the target volume implemented under the guidance of the 3D treatment plan should be called 3D conformal radiation therapy. However, the three-dimensional conformal radiotherapy for head tumors using stereotactic radiosurgery (SRS) systems is different from the equipment and appendages for three-dimensional conformal radiotherapy for trunk tumors. There are also some differences in operating techniques. Many literature reports generally describe Three-dimensional conformal radiotherapy for head tumors using the SRS system is called Stereotactic radiotherapy (SRT), and radiotherapy for trunk tumors using body mounts, MLC, or low melting point lead blocks is called three-dimensional conformal radiotherapy. [3D-CRT]. In fact, SRS, FSRT, SRT, 3D-CRT, and stereotactic brachytherapy (STB) should all belong to the category of stereotactic radiotherapy. The implementation of 3D conformal radiotherapy mainly depends on the following four aspects of technical support:

[1] Multi-leaf grating system MLC, there are many types, including manual, semi-automatic and fully automatic. It also varies in size and number of leaves. The purpose of the MLC system is to replace lead blocks; to simplify the shaping process of irregular irradiation fields, so that the number of irradiation fields can be increased to improve shielding of normal organ structures; static irradiation fields and single frames using multi-leaf gratings The angle can be used to adjust the flatness of the wire harness; the blade can be moved as the frame rotates to adapt to the dynamic adjustment of the irregular tumor shape.

2 Three-dimensional radiotherapy planning system, its main feature is the treatment display based on three-dimensional reconstruction of CT images. For example, the Beameye view (BEV) function can display the conformity of the shape of the irradiation field and the tumor at any incident angle of the ray and the shielding of adjacent key structures. It is a key function to achieve "conformal irradiation". [Room-view, RV] function, which can display the treatment situation seen in any position in the treatment room. This function compensates for the lack of BEV in the perspective of the wire harness, especially when setting the center depth such as rays. Multiple wiring harnesses can make appropriate geometric adjustments to the treatment technique. Dose-volume histogram display [Dose-volume histogram, DVH] function, can show the rationality of the treatment plan, the iso-dose curve includes the treatment volume state and the evaluation of the entire plan.

[3] Computer-controlled radiation therapy machines, a new generation of linear accelerators, some high-end cobalt 60 therapy machines and after-installed therapy machines are controlled by computers.

[4] Positioning, fixing, and verification systems, mainly including body fixation frames, head and neck fixation frames, thermoplastic masks, vacuum pads, and devices that limit visceral activity to increase the accuracy of repeated positioning; confirmed images of the irradiation field and some verifications device. Although the clinical application of 3D conformal radiotherapy technology has obtained high-dose radiation uniformly distributed in the target area, while minimizing exposure to normal tissues; theoretically, it can greatly improve the local control rate of tumors, but in clinical practice An important question encountered is: how to determine the range of treatment volume? The recognition and determination of the edge of the treatment volume largely depends on the imaging technology and the operator's level of image reading. Therefore, in 3D conformal radiotherapy, the accuracy of the determination of the treatment volume is closely related to the understanding of the tumor range. . Obviously, the modern imaging diagnosis technology has an important role in the implementation of 3D conformal radiotherapy.

Intensity Modulated RT (IMRT)

Intensity-modulated radiotherapy (IMRT) is an abbreviation for three-dimensional conformal intensity-modulated radiotherapy. Compared with conventional radiotherapy, its advantages are:

[1] Adopted precise body positioning and stereo positioning technology; improved the positioning accuracy, positioning accuracy and irradiation accuracy of radiotherapy.

[2] The precise treatment plan is adopted: Inverse Planning [Inverse Planning], that is, the doctor first determines the maximum optimized plan results, including the target area's irradiation dose and the tolerated dose of the sensitive tissue around the target area, and then the computer gives the realization The method and parameters of the result, thus realizing the automatic optimal optimization of the treatment plan.

[3] Accurate irradiation is used: the weights of the various beams in the field can be optimally configured so that the distribution of the high-dose area in three dimensions can achieve Ono irradiation and Ono additional dose irradiation [Simultaneously Integrated Boosted (SIB)] in one plan. IMRT can meet the "four most" desires of radiotherapy doctors: that is, the target area has the largest radiation dose, the normal tissue outside the target area has the smallest radiation dose, the target area is positioned and irradiated most accurately, and the target area has the most uniform dose distribution. . The clinical results are: significantly increase the local control rate of tumors and reduce radiation damage to normal tissues.

The main implementation methods of IMRT include:

[1] Two-dimensional physical compensator intensity modulation,

[2] Multi-leaf collimator static step adjustment [Step & Shoot],

[3] Multileaf Collimator Dynamic Intensity Adjustment [Sliding Window],

[4] tomography,

[5] Electromagnetic scanning IMRT.

The current common clinical application is the electric multi-leaf grating intensity modulation technology. Studies of applying IMRT to treat tumors in head, neck, skull, brain, chest, abdomen, pelvic cavity and breast have all reached positive conclusions. Zelefsky et al. Used IMRT and 3D-CRT to treat prostate cancer patients, respectively, and the target area dose distribution IMRT was significantly better than 3D-CRT at the same prescription dose [81Gy]; the incidence of early and advanced radiation injury in rectal cancer was also IMRT Significantly lower than the 3D-CRT group. Using IMRT to treat head and neck tumors can not only better protect parotid glands, brainstems and other organs, but also use Ono's additional dose [SIB] technology to further improve the efficacy. Using IMRT technology for breast-conserving postoperative radiotherapy for breast cancer can improve the target area dose distribution and better protect the lungs and heart. Many units in China have adopted IMRT technology for radiotherapy for nasopharyngeal cancer, breast cancer, esophageal cancer, and lung cancer, with positive preliminary conclusions. There is no doubt that IMRT will become the mainstream method of radiation therapy in the future.

Imaging Guided RT [IGRT]

Increasing the target dose of radiotherapy is the key to improving the local control rate of tumors. Because the spatial position of tumors and surrounding normal tissues is constantly changing during and during treatment, if these changes and errors are not given sufficient attention, it may cause tumors. Off-target and / or normal tissue damage increase, reducing efficacy. The influencing factors of position uncertainty during radiotherapy can be summarized into two aspects: one is the systematic error of the irradiation field position, which refers to the error of data transmission during the positioning, planning and treatment stages and the design, marking or treatment assistance Positional errors of objects such as compensators, stoppers, etc .; Second, random errors in the position of the irradiation field: Refers to changes in the patient's anatomical position due to the position of the technician during each treatment and the fractional treatment, such as respiratory movements, bladder Positional differences caused by filling, peristalsis of the small intestine, pleural and ascites fluid, and tumor enlargement or contraction. Clinical practice and experimental studies have confirmed that the above errors will have a significant effect on the dose distribution of tumor target areas and surrounding normal tissues, and are more pronounced in conformal and intensity-modulated radiation therapy. In recent years, electronic field imaging systems (EPID), CT, and other equipment have been able to conduct more precise research on the uncertainty of the target area, including verification of position and dose, and correct it through offline and online methods. The new EPID is installed on the accelerator, and it can calculate and verify the dose distribution while performing the position verification. At present, there are also CT-medical accelerators and respiratory control systems. If the therapeutic machine is combined with imaging equipment, the relevant imaging information is collected during the daily treatment to determine the target area for treatment, reaching the daily target, which is called imaging guidance. Radiotherapy [IGRT].

Biologically Conformal RT [BCRT]

In the traditional concept, the irradiation field in the external irradiation plan should completely cover the tumor target area indicated by CT and MRI of the anatomical image and give a uniform dose of irradiation. For example, radiotherapy for prostate cancer, due to the limitations of traditional imaging techniques, we cannot fully show the difference between cancer tissue and normal prostate tissue, and the entire prostate is included in the target area, which is not consistent with the theory of radiotherapy. And more importantly: within the tumor target volume, the distribution of cancer cells is uneven. Due to different blood transport and cell heterogeneity, the radiosensitivity of different cancer cell nuclei is very different, giving the entire target volume The area is irradiated with a uniform dose, and some cancer cells may survive due to insufficient dose and become the source of recurrence and metastasis; if the entire target area is overdosed, it will cause serious damage to surrounding sensitive tissues. In addition, the dose response and tolerance of normal tissue structures within and around the target area are different; even for the same structure, the tolerance of its substructure may be different, which will inevitably affect the expected target of radiotherapy.

According to the theory of biological target area (BTV), the biological target area can be initially defined as: areas with different radiosensitivity in the therapeutic target area determined by a series of tumor biological factors. These biological factors include:

[1] Hypoxia and blood supply;

[2] Regulation of proliferation, apoptosis and cell cycle;

[3] Changes in oncogenes and tumor suppressor genes;

[4] Wetting and transfer characteristics. These factors include the difference in sensitivity of tumor cells in the target area of the tumor and the sensitivity of normal tissues, and these biological targets can be displayed by modern advanced comprehensive imaging technology, which lays a solid foundation for bioconformal radiotherapy and expands space. For example, magnetic resonance spectroscopy (MRS), positron emission tomography (PET), and single photonmission computer tomograpy, which mainly reflect the functions of organs and tissues, belong to functional imaging SPECT) and other images mainly reflect the morphological and anatomical structure changes, X-rays, CT and other images belonging to the category of anatomical image fusion technology. These image fusion techniques are used in radiotherapy planning systems as the basis for bioconformal treatment planning. In recent years, the functional imaging technology represented by PET, SPECT, MRS, etc. has developed rapidly. FDG-PET can be used to reflect the metabolism of tissues; hypoxia imaging agents such as fluoronitroimidazole [18-FMISO] can be used to detect tumor hypoxia in vitro; 11C-methionine can be used to detect tumor protein metabolism; 18F-thymus Pyrimidine nucleoside can detect tumor nucleic acid metabolism and so on. Studies have shown that the application of PET can change the radiotherapy regimen of at least 30% of tumors. And with the application of CT-PET, the performance and quality of images have been greatly improved. The application of functional MRI (fMRI) technology is also exciting. FMRI can display brain function, reflect oxygen supply and angiogenesis, and provide important information for brain surgery and brain radiotherapy, which can maximize the important functional areas of the brain. protection of. Using special pulse-echo dynamic imaging technology, it can scan tissue blood perfusion and blood-brain barrier permeability, not only can distinguish normal and tumor tissues, but also assess the type and grade of tumors, predict and evaluate the efficacy.

At present, the development of IMRT has brought the physical conformity of radiation therapy dose distribution to a fairly ideal level, and biological and functional imaging has created a new era of biological conformity. There is a multidimensional adaptation of physical conformity and biological conformity. Shaping therapy will definitely become the development direction of radiotherapy for tumors in the new century. Chao et al. Used Cu-ATSM as a PET hypoxic tracer and conducted phantom and human studies on head and neck tumors. The results showed that using Cu-ATSM PET and the reverse planning system to receive 80Gy on GTV, PET was shown. Hypoxic target doses can reach 80 Gy, while most of the parotid doses are less than 30 Gy. The results of this study confirm the possibility of Biological Intensity Modulated RT. Researchers at the University of California use proton nuclear magnetic spectroscopy for radiation therapy planning and treatment evaluation of prostate cancer. The relative concentration of choline is higher in the tumor area, while the citric acid concentration is higher in normal prostate tissue and benign hyperplasia area. Based on this difference, they are using the IMRT program to give higher doses of radiation to the high choline / citrate area, which is also a treatment model derived from biocompatible IMRT.

Three-dimensional stereotactic radiotherapy technology has developed rapidly in the last two decades of the 20th century. Although there are still many problems to be overcome, the advantages it shows are unquestionable. Its establishment, development and improvement signify the entry of tumor radiotherapy. The era of "precise positioning, precise planning, and precise treatment" has arrived. Three-dimensional stereotactic radiotherapy has also established a new high-tech platform for clinicians, radiation physicists, and radiobiologists of radiation oncology. Technical requirements.