Radioactive particle implantation therapy is a newest method of tumor treatment. The radioactive 125I, which has the effect of killing tumor cells, is sealed in a tiny titanium shell, called “sealed seed source” or “particle”, and then a set of special instruments is used to place the radioactive particles directly into the tumor. The gamma rays emitted can kill tumor cells, thus achieving the same effect as scalpel removal, so it is also called “particle knife”. This is a minimally invasive technique supported by imaging technology, which can achieve high dose in the tumor target area and no dose in the surrounding tissues; it is more effective in local progressive tumors that are inoperable.
The traditional radiation therapy (external radiation) technique is to irradiate cancerous tissues with high intensity, and the surrounding normal tissues will inevitably be damaged by radiation to different degrees. Although with the development of radiotherapy techniques, the amount of radiation to normal tissues can be reduced to some extent, it is sometimes difficult to achieve high doses of irradiation. The implantation of radioactive particles is based on the tumor morphology, and the dose of radioactive particles and the distribution of particles are decided by the precise calculation of the three-dimensional stereotactic planning system (TPS). Moreover, since the attenuation of radioactive particle intensity is inversely proportional to the square of distance, the damage to the surrounding normal tissues is smaller, and the normal tissues are better protected, and the tumor can be irradiated at a close distance, so that the tumor area gets a higher radiation dose.
125I particles can continuously release γ-rays at low doses, which can cause double-strand breakage of tumor cells by directly acting on their DNA, in addition to directly ionizing water molecules in the body, generating free radicals, promoting apoptosis of tumor cells and preventing tumor cells from reproducing, thus achieving the purpose of treatment.
Radiation particle brachytherapy started in 1901 when PierreCurie invented radium tube, a radioactive particle that could be implanted in the body. However, it was not until the late 1980s, with the successful research of Treatment Planning System (TPS), that 125I particles became a hot spot for the treatment of tumors and have been used more and more widely.
I. Characteristics of 125I particles.
Seed source structure: outer shell material titanium tube outer diameter 0.8mm, length 4.5mm, wall thickness 0.05mm, inner core material silver wire size φ0.5X3mm, silver wire surface layer plated with 125I isotope.
Half-life: t1/2=59.6 days
The main emitted photon energy is: 27.4Kev and 31.4Kev χ-ray; 35.5Kev γ-ray, a low-energy radiation.
Lead half-value layer: 0.025mm
Cell tissue half-value layer: 20mm
II. Dose selection and implantation method of 125Ⅰ particles
According to the different morphology of tumor, the approximate volume is calculated by the length, width and height of the target area, which is used to calculate the number of implanted particles, so as to achieve the required peripheral dose (matched peripheral dose, MPD). The uniform dose for the treatment of malignant tumors is set as 95% of the volume of the tumor target area should reach the prescribed dose (PD), i.e. Vl00>95%. The tumor target area dose generally does not exceed 2PD to reduce the damage to normal tissues around the periphery, but if 90% of the tumor target area dose does not reach PD, the recurrence rate is significantly higher. The American Brachytherapy Association requires that a treatment plan must be in place prior to radiation particle implantation to establish the expected dose distribution, and the treatment planning system (TPS) must calculate the dose to determine the uniform prescription dose. The dose is calculated by the treatment planning system (treatment planning system TPS) to determine the uniform prescribed dose. Using CT, MRI and other imaging techniques, the target area is determined, the PD value is calculated, the number of implanted particles, their activity and total activity are obtained, the dose distribution is observed, and the position of the guiding needle is adjusted to achieve the best distribution to maximize the killing of tumor cells and minimize the damage to the surrounding normal tissue. After implantation, the dose must be evaluated and verified, i.e. postplan, so that the efficacy and complications can be evaluated more objectively and truly.
125ⅠParticle inter-tissue implantation can be divided into intraoperative implantation under direct vision in the operating area and implantation under the guidance of imaging technology. The intraoperative implantation method refers to the direct exposure of the primary lesion, and for lesions that can be treated with individual radiation therapy, the particles are implanted into the tumor bed, lymphatic drainage area or tumor body according to the treatment planning system; for lesions that cannot be treated with individual radiation therapy, the particles are implanted into the residual lesion area according to the frozen section and clear pathological diagnosis, and the extent of resection is reduced as much as possible, and the implantation is carried out in parallel with the blood vessels to reduce The implantation should be carried out in parallel with the blood vessels to reduce postoperative complications.
C. Indications for 125I particle therapy for tumors.
1) Locally advanced tumors that cannot be removed surgically.
2) Advanced age, impaired cardiopulmonary function, unable to tolerate surgery or unwilling to operate.
3) Localized invasion and tumor residue expected during surgery.
4)Cases with poor or failed external irradiation effect, etc.
5)Malignant tumor of salivary gland in children.
6)Tumor in close proximity to facial nerve and need to preserve the nerve.
7)Recurrent salivary gland cancer.
IV. Application of 125I particles in oral and maxillofacial malignant tumors
The use of 125Ⅰ particles in systemic malignant tumors such as prostate cancer, liver cancer and cranio-cerebral tumors is much earlier than that of oral and maxillofacial head and neck, and the technology is relatively more mature, so it has a strong significance for the future brachytherapy of malignant tumors in this area.
As a unique area, the oral and maxillofacial region is connected to the cranial central nervous system and the lower extremities of the torso, which is a narrow pathway for various connected systems. The blood system, lymphatic system and nervous system are widely distributed in the area. Because of the tissue anatomical characteristics, it makes the development of each advanced technology later than other parts of the body, and has greater risk and higher requirements for the control of complications.
Radioactive particles can be applied to adenocarcinoma of salivary gland, malignant tumor of parotid gland, early tongue cancer, recurrence after oral cancer and local lymph node metastasis of oral cancer, etc., which can obtain better results.
V. Status of particle implantation treatment in the Department of Stomatology of Shandong Provincial Hospital
Since 2008, the Department of Stomatology of Shandong Provincial Hospital has carried out radioactive particle brachytherapy for oral and maxillofacial-head and neck malignant tumors, and has treated more than 500 patients with satisfactory postoperative effects, especially in patients with salivary gland, jaw bone and advanced oral cancer. In the treatment research of this project, the department has formed a set of personalized treatment plans for different disease nature and different patients, especially the salivary gland tumor treatment has been done as a routine treatment for postoperative malignant tumors. At present, the Department of Stomatology of Shandong Provincial Hospital is the first and the only medical unit in Shandong Province to legally implement this project, and the technology of radioactive particle brachytherapy for oral and maxillofacial-head and neck malignant tumors is in the forefront of this field in China, always leading the development of this project in Shandong Province.
Sixth, 125I particle implantation precautions.
1.The 125I sealed seed source for treatment is implanted for a long time.
2. Do not forcibly put in or take out the seed source from the implanted test tube, needle or seed source clip, otherwise the outer wall or the welding of the seed source will be damaged, which will cause 125I to be released into the environment or into human body fluid. If the seed source is found to be damaged, the seed source should be sealed and disposed of as soon as possible according to the disposal method of radioactive waste, and the surrounding environment should be checked to see if it is contaminated.
3. The titanium alloy envelope of this product has good anti-corrosion performance under normal use. However, the seed source cannot be exposed to concentrations exceeding 1N acid or alkali. The seed source is not affected by general solvents, such as acetone, alcohol or mild decontaminants.
4. Operator safety: The 125I sealed seed source is radioactive and must be operated with proper protection. Only those personnel who are trained and experienced in the safe use of radioactive substances and who are certified by a national authoritative government agency as qualified to operate radioisotopes should operate the 125I sealed seed source.
(1) All steps of the implantation procedure are to be designed in advance to minimize the radiation impact on people. The operator is to be monitored for radiation dose and personnel must wear an exposure dosimetry soft piece or radiation dosimeter.
(2) Operation of the 125I sealed seed source: Operation of the 125I sealed seed source should be performed with sufficiently thick shielding. The shielding half-thick layer of lead against 125I rays is 0.025 mm and the tissue is 20 mm. Therefore, a 0.25 mm thick layer of lead can reduce more than 99.9% of the radiation. When operating with forceps, the operator and the seed source should be kept at a certain distance. The seed source should be gently gripped so that it is not damaged. The seed source should not be held directly by hand. If protective isolation is not used, the operator must keep a certain distance and do it as fast as possible to minimize the effects of radiation.
(3) Occasional damage to the 125I sealed seed source: Although the 125I sealed seed source has strong structural integrity, improper handling or extrusion can cause the seed source to release “free” 125I. If this occurs, the damaged seed source should be placed in a sealed container and movement of personnel should be restricted to prevent the spread of radioactive contamination. Prevent the spread of radioactive contamination, decontaminate the area and personnel in accordance with established procedures, and conduct thyroid examinations on the accident site and surrounding personnel. Since the seed source is very small, it is generally difficult to find the fallen seed source by eye observation. When operating a 125I sealed seed source, it should be equipped with a radiation detector capable of detecting up to 30 Kev. In case of seed source loss or other accidents, the relevant department should be notified immediately.
5. Protection of treated patients: All patients, family members should be informed of the characteristics of the implanted 125I sealed seed source and the need to take appropriate radiation protection measures. All patients should be informed that one or more seeds may detach during the course of treatment as the tumor shrinks and becomes smaller. Whenever and wherever a seed source is found, it should be picked up with a spoon, placed in a sealed jar or other container, and placed in an untouchable place in the home.
6. Disposal of unused 125I sealed seed sources: Unused surplus 125I sealed seed sources should be shipped to an authorized radioactive waste disposal company if they need to be disposed of, and not disposed of as ordinary garbage.
VII. Instructions for treatment
1.Before treating patients with seed sources, patients should be informed about the therapeutic characteristics and precautions of the seed sources.
2. All radioactive products are hazardous if they are handled, used, stored, transported or destroyed in an improper way, or if relevant regulations are not observed. In order to avoid hazards, it is necessary to strictly follow the relevant regulations and the requirements specified in this instruction.
3.There must be trained and qualified staff to take and use the seed source. Staff must wear appropriate protective clothing and be equipped with personal radiation dosimeters to access and use the seed source.
4, in order to reduce human radiation to a minimum, take, use the seed source, before ensuring the smooth operation, should minimize the operating time, as far as possible to increase the distance between the human body and the seed source and the use of adequate shielding. At the same time, suitable radiation and pollution detection instruments must be used for monitoring.
5. Although the seed source is classified as a sealed product, routine surface contamination checks should be done on the operating area and on apparatus in contact with the seed source.
6.The seed source should be used at room temperature. Temperature exceeding 250℃ may cause changes in the dose distribution around the particles.
7.The seed source should be handled carefully, do not squeeze or drop it, do not break the outer shell of the seed source in any way, and it is strictly prohibited to make any morphological changes to the seed source (such as squashing, bending, etc.) to prevent radioactive leakage.
8. The seed source cannot be used directly for insertion, and suitable apparatus such as syringes and templates should be used.
9.The seed source is not sterilized at the factory. The seed source should be sterilized before use.
10. All treatment procedures should be planned in advance to minimize the radiation exposure of personnel.
VIII. Breakage, loss and disposal of the seed source
1.If the seed source is found to be damaged, it should be dealt with in a timely manner, and if it causes significant consequences, it should be reported to the relevant departments at higher levels.
2.If the seed source is found to be lost, the search should be promptly organized and reported to the relevant departments at higher levels.
3, due to decay and other reasons, resulting in the seed source has no use value, or broken seed source and its radioactive contaminants, etc., can not be abandoned at will, should be treated as radioactive waste, it will be sent to the authorized radioactive waste disposal institutions on behalf of the treatment.
4, should be the minimum control of radioactive waste generation, radioactive waste packaging, transportation should be carried out in accordance with the relevant national regulations.
Nine, radiation protection
1.Before taking or using the seed source, a detailed action plan should be prepared to assess the possible dangerous situation. The transfer of seed sources must be recorded and must be kept for the appropriate time according to the relevant regulations. Accident plans must be developed for foreseeable accidents.
2. Establish a “control zone” when the immediate dose rate exceeds 7.5 μSv/h. Designate a specific room or building, or delineate a certain area, and have clear signs.
3.Be careful to avoid unnecessary irradiation of employees or patients by X-rays and γ-rays.
4. Parameters for minimizing personnel irradiation.
①Time: Minimize the time for personnel to approach the source.
The total number of doses received during the operation of the seed source is directly proportional to the time taken to complete the work.
If the working time is doubled, the dose received is also doubled.
★ A good work plan helps to reduce the irradiation time to a minimum.
② Distance: Increase the distance between the source and personnel to the maximum.
Radiation is inversely proportional to the square of the distance. For example, if the distance is doubled, the dose rate is reduced to the original
1/4, but if the distance is reduced by half, the dose rate increases by a factor of four.
Note: The dose rate at 1 mm is 10,000 times greater than at 100 mm.
★ Use tweezers to manipulate the seed source and prohibit direct contact with hands.
③Shielding: Shield with e.g. lead glass where possible.
Dense, high atomic number substances such as lead can better reduce irradiation. A sheet of lead only 0.25 mm thick can reduce 99.9% of the gamma radiation radiated by 125I.
5, with a suitable calibrated dosimeter to check the actual dose received by the personnel involved in the work.
6.Check the workplace for contamination after each procedure with a suitable testing instrument. The seed source is a sealed radioactive source, therefore, no radioactive material should leak out during normal use, but if contamination is found, it should be removed immediately.
7.Must consider the disposal method after the death of a patient receiving seed source implantation treatment.
8. Special protection is generally not required for personnel providing care for patients receiving seed source treatment and for the patient’s accompanying family members.