"You can't reason without any evidence, and in that case you can only go astray. Being based on facts is always the starting point for us to think about problems. —Sherlock Holmes Classic Quotations.
Radiation is a delicate and complex process, with multiple links closely interlocked, and each step will have an impact on the final effect. For modern radiotherapy in the "Three Essence Era", precise positioning, precise planning, and precise ** are required.
In investigating a case, it is necessary to look at the facts and explain the evidence. This is especially true of radiation, which is a medical tool. In radiotherapy, how to "see is believing"?
Sun Yat-sen University Cancer Prevention and Treatment Center Radiologist Shang Lintao Teacher is talking! Today, Mr. Shang will introduce you to the first essence in the "three essence era" of modern radiotherapy - precise positioning.
The machine is cold, the ray is ruthless, and we want to be the best teacher with temperature.
Shang Lintao
Sun Yat-sen University Cancer Center.
Radiologist, Sun Yat-sen University Cancer Prevention and Treatment Center; Correspondent of China Anti-Cancer Association, Lecturer of Cancer Prevention and Treatment in Guangdong Province.
He is good at the design and production of body position fixation of radiotherapy patients, CT simulation positioning and MR simulation positioning technology, the implementation of radiotherapy, and the popularization of radiotherapy-related precautions.
He has won the third prize of the first Guangdong Provincial Cancer Prevention and Treatment Science Contest (speech category) and the Excellence Award of the 4th Southern Health Science Contest (** category).
Precise radiotherapy, quality control first. Radiotherapy quality control is the guarantee of patient safety!
1.Analog Positioning: What is it? Do what? Why?
The human body is like a complex labyrinth, how to accurately detect the location to be irradiated and determine the size of the range?
The patient lies in the mold in a relaxed state, and the first-class master scans the CT and MRI images of the patient and the mold, and at the same time establishes a spatial coordinate system with the help of an external laser and three marker points to obtain human image data with a positioning systemThis step is called analog positioning.
To put it simply, it is to simulate the state of ** and carry out "satellite positioning" on the tumor, so that doctors can accurately circle the "bad guys" (target areas) on the "satellite map" where the "bad guys" (target areas) are and where the "nearby people" (important endangered organs) need to be protected.
CT simulation positioning.
2.Precautions when CT simulation positioning
Read carefully and prepare rigorously
Prepare accordingly in strict accordance with the doctor's instructions and guidelines, such as:
For example, patients with urological tumors need to empty the rectum and fill the bladder before positioning (defecation before holding urine);
Abdominal patients with liver cancer need to fast for 3-4 hours;
Head and neck patients need to have the broken tooth extracted first;
Rectal cancer patients are located before 15 2 hours orally diluted contrast medium for intestinal lumen development, etc.
Tell your health care provider if you have allergies
CT contrast examination is an important imaging method to find the location of the tumor and determine the size of the target area in CT simulation positioning, which increases the contrast between tissues through intravenous injection of iodine contrast agent, which can improve the display rate of lesions and solve the problems that cannot be found by non-contrast scanning.
However, there are certain risks associated with intravenous iodine contrast agents, and if there is a past history, a history of allergies, heart, liver and kidney insufficiency, etc., the radiotherapy doctor and ** should be informed in advance. Depending on the patient's condition, the radiation therapist may choose to use a noncontrast scan alone or an allergy drug.
Listen to the request and cooperate carefully
When performing CT simulation, the patient first applies a mold to return to a fixed position.
At the same time, the positioning area needs to be exposed, so patients with different parts need to take off their tops or pants, and pay attention to removing jewelry, underwire underwear, dentures, wigs, etc.; Finally, the ** teacher will mark the placement point on the patient's body surface and paste the lead dots; For breast patients and patients with scars and scalpel cuts, lead wires are also attached to important locations.
Calm down and relax your body
Whether it is a body surface marker or a CT scan, even breathing and remaining motionless is the best cooperation for the patient.
The body surface marker is an important reference for the accurate position of the master in the future precision radiotherapy. No, no, no
Clear CT scan images are an important basis for physicists to make precise radiotherapy plans. No, no, no
Note that it is normal for the body to feel slightly warm during CT scanning, but if symptoms such as dizziness and difficulty breathing occur, raise your hands or legs in time, and the medical staff will deal with it as soon as possible.
Rest and observe and wait patiently
Do not leave in a hurry after the CT scan, you need to stay in the observation room for half an hour, and at the same time, you need to keep the venous access (do not withdraw the needle for the time being), so that allergic reactions and other discomforts can be administered in time.
Drink plenty of water for 24 hours after the scan to promote iodine contrast excretion.
In fact, the patient waiting here does not only refer to the half-hour observation time, but also the waiting time after positioning.
It generally takes 3-5 working days after simulated positioning, and the plan is made and verified by the plan.
3.After CT positioning, why do you need MR positioning? Are the two the same?
The answer, of course, is: no.
Due to the characteristics of fast CT scanning, the advantages of bony structure display, and the design dose for radiotherapy planning, it has always been the main simulation and positioning technology of radiotherapy.
However, the soft tissue resolution of CT is poor, with the development of precision medicine, for patients with many diseases, simple CT simulation positioning has gradually not been able to fully meet the requirements of precision radiotherapy, MR simulation positioning in nasopharynx, breast and other parts, can provide more accurate tissue and orientation information than CT, can meet the accurate identification of tumors, and better display the characteristics of endangered organs that need to be protected.
Compared to CT simulation positioning,MR Analog Positioning offers the following advantages:
The resolution of soft tissues is higher, and the tumor boundaries are displayed more clearly;
better distinguish between tumor-active and edematous tissues;
Functional imaging is available to provide richer information for efficacy assessment;
There is no radiation during the positioning process.
Since MR analog positioning has so many advantages, can we only do MR positioning and not CT positioning? I'm sorry to tell you: no!
Because MRI images do not have electron density information, it means that planning cannot be done from MRI images. At present, the method used is to scan a positioning CT + a positioning MR through the same body position and mold, and the MR image is used to delineate the target area after image fusion, and the CT image is used to calculate the dose.
CT-MR image fusion can provide richer information for delineating targets, endangering organs, and making plans.
4.Precautions for MR positioning
The precautions for MR positioning are roughly the same as those for CT positioning, but the following points are worth noting:
All metal items should be removed and placed outside for storage before inspection. Note: That's all! This is especially true for small items that are easy to overlook, such as keys, coins, lighters, etc.
There is a very strong magnetic field in the MR positioning room, just like a large magnet with strong suction, and the metal will be quickly adsorbed. The real suction and speed are not recommended for experiments, and it will cost you money if you damage the machine, and you and I will be scared.
When the MR simulation positioning, the patient's application mold and body position should be completely consistent with the CT simulation positioning to prevent the image from being unable to be fused due to inconsistent body position or body movement during the examination.
The MR analog takes longer to locate and is louder. During the examination, please wear headphones or cotton and earplugs, and pay attention to your physical condition, if you feel nausea, vomiting, dizziness and other physical discomfort, press the emergency bell or raise your hand in time to prevent accidents.
5.Department of Radiation Oncology vsImaging: What is the difference between CT and MR?
Doctor, I've had a CT done in the imaging department recently, why do I have to do it again in the radiation oncology department? ”
In their daily work, many patients preparing for radiation** often have such questions.
After the above, you know what CT simulation positioning and MR positioning are and how to do it. Is there any difference between them and the imaging examination, and can the CT and MR examinations done before be regarded as simulated positioning?
The purpose is different
CT and MR examinations: to show the anatomical structure, tissue morphology, and functional imaging that need to be seen, so as to achieve the purpose of finding lesions, diagnosing lesions, and evaluating curative effects.
CT and MR localization are the basis for ** tumors. Of course, CT and MR cannot be used for **, our radiation is like a missile, and the simulated positioning is equivalent to a precision guidance system, and the location of the tumor can be accurately struck in order to carry out a precision strike.
The construction is different
Analog positioning machine is generally performed by large-aperture CT (70cm-85cm) specially designed for radiotherapy department. Because when performing some analog scans, many third-party fixtures may be required, and if the aperture is small, it is not conducive to the patient's positioning.
The aperture of the CT and MR machines in the imaging department is relatively small, but the image quality is clearer.
The accessories are different
In addition to the scanning machine itself, a 3D laser light positioning system is also required in the simulation positioning machine room, which is not required by the imaging department. The analog positioning machine needs to use the same scanning flat bed as the ** machine, while the imaging department uses a curved bed.
Scanning technology
In the chest (lungs), 4DCT scanning can be used to simulate positioning, which can obtain images of different breathing phases, observe the range of motion of the target area, better delineate the target area, and formulate a radiotherapy plan.
In a nutshell, imaging examinations are used for clinical diagnosis, and radiation oncology is positioned for planning. Therefore, the examination of the imaging department cannot replace the simulation positioning.
- I am the end of the dividing line--- modern precision radiotherapy is a method that uses advanced imaging technology and computer technology to perform high-precision, high-efficiency and individualized treatment of tumors**.
Precision radiotherapy delivers high doses of radiation to the tumour area through a series of precise radiotherapy techniques – precise positioning, precise planning, precise ** while minimizing radiation damage to surrounding normal tissues.
Lin Tao, the ** teacher of medium and swollen radiation, is talking! Lecture 3 "Reset Verification: Mind You, It's Not Just a Drill"! >> Stay tuned! 
Remarks
The purpose of this article is to convey more medical information to medical and health professionals, and does not constitute any basis for diagnosis and treatment, and the content is for reference only.
AuthorSun Yat-sen University Cancer Prevention and Treatment Center Radiologist Shang LintaoMore readingRadiotherapy is also available to be customized, your personalized mold!Shang Lintao, the middle swollen ** teacher, is talking! Gong Jian, Zhongnan Hospital, Wuhan University: Five-level quality control of tumor radiationPrecision Radiotherapy, Quality Control First 2024, Start with Understanding Radiation**!