Key words: thoracic neoplasms/radiotherapy; accuracy and correct reproducibility of radiotherapy/instrumentation and equipment are one of the key factors affecting the efficacy of radiation therapy. How to ensure the accuracy and repeatability of the positioning is the radiotherapy industry Has always been concerned and explored topics. The fixing device is an important guarantee for the accuracy and repeatability of the position. Because head and neck tumors have a large head and neck movement and are prone to position errors, the fixing device was used very early and developed from the early simple head and neck holders. Today's head and neck fixed masks and head stereotactic radiotherapy fixtures ensure the accuracy and repeatability of head and neck tumor positioning. The majority of patients with thoracic tumor radiotherapy did not use the fixed device plus respiratory motion, resulting in poor accuracy and reproducibility of the position of the chest tumor. The radiology and treatment engineers in our hospital used the negative pressure vacuum for conformal intensity modulated radiation therapy. The pad is used as a body-fixing technique, and the use of a negative-pressure vacuum pad as a fixed device for conventional radiotherapy of a thoracic tumor plays a very good role. The method is now described as follows.
1 Materials and methods 1.1 Materials Negative pressure vacuum pad, vacuum pump; mainly used for the treatment of breast cancer patients with esophageal cancer, lung cancer, thymoma, breast cancer, Hodgkin's disease.
1-2 Methods Place the vacuum pad evenly on the flat bed. According to the need of radiotherapy for breast tumor patients, supine or lying prone on the negative pressure vacuum pad, the arms can be placed on both sides, head, side arm outspread or fork etc. The two sides of negative pressure vacuum pad folded close to the sides of the patient's body, with a vacuum pump to -0-8p closed after the suction tube, in the vacuum pad on both sides of the lower edge of the flat rib, xiphoid, acromioclavicular joint, earlobe Place four pieces of tape at each place. Use the scratch liquid to draw marks on the adhesive patch and extend it to the body. Mark the name, disease, and disease period. Hospitals with conformal and intensity-enhancing equipment can be made directly on conformally modulated carbon fiber beds, and they can also be made of wood to make them similar to a conformal bed.
1-3 Scan When performing CT or MRI scan, place the prepared negative pressure vacuum pad on the radiotherapy special bed (flat bed) to assist the patient in lying on the vacuum pad so that the skin painting marks are exactly the same as the vacuum pad painting marks. After the scan to do a treatment plan, to simulate positioning machine positioning, verification.
1-4 Calibrate the laser light before positioning and place the negative pressure pad on the simulated positioning bed. The patient lies down so that the skin marks are exactly the same as those on the vacuum pad. According to the requirements of the treatment plan, the laser will be positioned on both sides of the cross laser. The line is marked on the vacuum pad (applied cloth) and extended to the body. The median laser line directly marks the patient's body. Makes the body exactly the same as the vacuum pad model from three dimensions.
1-5 Position the laser light before setting the position. Use negative pressure vacuum pad for each position to ensure that the position mark of the patient is exactly the same as that on the vacuum pad. Instruct the patient to breathe calmly to reduce the treatment target movement caused by breathing. By moving the vacuum pad and the treatment bed left and right, the median laser line is completely coincident with the median laser line marked on the patient's body; the treatment bed is moved up and down and back and forth so that the cross laser lines on both sides completely coincide with the mark cross line on the vacuum pad.
After the positioning of the 1-6 camera verification film is completed, a 2 mm diameter, 1 cm long lead wire is placed in the center of the patient's body field and fixed with a tape. The patient is seated and the same cross lead wire is placed on the center of the vacuum pad and fixed with adhesive tape. Repositioning the position (two lead wires should be coincident) The radiography is called positioning, taking the patient to the accelerator room and setting it according to the program. The 0-1Gy dose is called the pre-treatment film. After the end of the treatment, the radiography is called the treatment. After the film.
2 Results Through the comparison of 20 cases of esophageal cancer patients before and after treatment with the positioning film, the error 3 to discuss the actual radiotherapy process, the occurrence of deviation in position is inevitable, Ferri et al 11 reported Hodgkin's disease Without a special fixture, the error rate of the setting error>6mm is 14%, and the longitudinal displacement is 23mm. Wang Fan et al. reported the use of an imaging system to study the reproducibility of the setup. The results showed that the head and neck neoplasm using the mask The correctness of the position is higher than that of the chest and pelvic cavity, and the worst is the chest tumor. The mean longitudinal movement of the chest is (2-4±1-4) (3-0*1-3) mm, and the patients with lateral movement of esophageal cancer move. (2-9 * 1-4) mm, lung cancer patients move (2-6 * 1-7) mm. Causes the chest to be prone to errors in positioning and mobility is mainly due to: Breathing movements make the isocenter when The full reproducibility of the field is difficult, the depth of the isocenter is inaccurate due to breathing, the laser positioning point is not easily aligned due to different skin pulling, and the two upper limbs are not fixed, and the negative pressure vacuum pad can effectively overcome the isocenter depth error, laser Inaccurate positioning points and the disadvantages of unfixed upper limbs In addition, the negative pressure vacuum pad on both sides blocks the lateral movement, which greatly improves the accuracy and repeatability of the position. In addition, the negative pressure vacuum pad is easy to use and the price is moderate (thousands of yuan), which can be used repeatedly. The author thinks it is ideal. Conventional radiotherapy for chest tumors uses a fixed device. Due to the small number of verifications, it needs to be further validated using the imaging system.
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