MindMap Gallery Medical - Brachytherapy Technology
This is an article about brachytherapy technology, which places a packaged radioactive source directly into the tumor site through a source tube for irradiation.
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brachytherapy technology
Radiation Therapy
brachytherapy
Radionuclides
After-installation
teletherapy
X-ray, electron beam
Linear Accelerator
Overview
Place the packaged radioactive source directly into the tumor site through the source tube for irradiation
The development history of brachytherapy
The first radium needle interpolation was performed in 1905. Marie Curie encapsulated radium elements into tubular line sources, which were the earliest application treatments and close-range treatments for skin cancer and cervical cancer.
In 1919 Regelld and Lacassayme created and developed the Paris method, known as low-dose long-term treatment
Manchester Law was established by Paterson and Parker in 1932
In 1953 Hinschke proposed the after-loading technology
In the 1960s, Chessague Pierguing and Duterix developed the Paris system, and remote-controlled after-treatment machines appeared.
Modern brachytherapy in the 1980s replaced traditional brachytherapy
Irradiation methods and types of radioactive sources
Irradiation method
Endovascular and intracanal treatment
inter-tissue interpolation technique
Seed implantation (permanent implantation)
surface dressing treatment
Placement of radioactive sources
manual
Manual operations are mostly limited to low-dose-rate, easy-to-protect radioactive sources.
After-installation technology
Post-loading technology is a technology that first places the source applicator in the natural cavity of the human body close to the tumor, implants a pipe or hollow needle into the tumor, and then introduces the radioactive source. These are all used in computer-programmed brachytherapy equipment.
Commonly used radionuclides
Radium-226: low energy, only used for close range irradiation
The complex energy spectrum has a protection problem of up to 3.8mev. Long half-life and environmental pollution. Radon gas leakage. Long half-life, serious damage to normal tissue, should be banned medically
In 1934, artificial radionuclides were discovered and the first attempt was made to apply Ir-192 clinically.
Ir-192 has become the most widely used radioactive source for brachytherapy due to its moderate energy and high specific activity.
The miniature Ir-192 source is 1mm in diameter and replaces the cs-137 tube source and particle source
Radioactive sources must meet
Sufficient penetration into tissues
Easy radiation protection
Half-life: not too short, not too long (especially for permanent implants)
Easily made into micro sources (more active)
Brachytherapy clinical dosimetry
Dose distribution and characteristics of radioactive sources
The dose angular distribution of an ideal point source is concentric circles
Radial dose attenuation of nuclide in water
The inverse square law is the main factor affecting the dose distribution around the radioactive source and is basically not affected by the radiation energy.
Spatial dose angular distribution of micro-cylindrical sources
Dose distribution characteristics around the radioactive source
The local dose reaches the edge and then the dose drops suddenly
The dose distribution within the irradiation range is uneven and is high near the source. Generally, there is no uniformity requirement.
Near the source, the attenuation of the line source is greater than that of the ideal point source. When the distance from the source is more than twice the length of the line circle, the attenuation of the two is basically the same. Source step length. Available in 2.5, 5, and 10mm grades
Physical quantities and unit systems of brachytherapy
Dose distribution around the radioactive source
brachytherapy dosimetry system
How to use the type of radioactive source, the method of intensity application and the geometric settings. At the same time, the system also clarifies the measurement representation and calculation method.
Stockholm System
paris system
The string sources encapsulated in plastic tubes at equal distances are linear and parallel to each other. The equal centers of the line elements are located on the same plane. The sources are equally spaced from each other and arranged in a square or equilateral triangle. The linear activity of the sources is uniform and equal. value, the line originates from the plane perpendicular to the center point
manchester system
It is a planar interpolation dose calculation system designed with radium-226 linear source in the 1930s.
Treatment tissue thickness is 1cm - single plane interpolation
Treated tissue thickness greater than 2.5cm--bi-plane interpolation
inter-tissue differential dosimetry system
According to the shape and range of the target area, multiple radioactive sources of certain specifications are directly implanted into human tissue according to certain rules with the help of a source applicator to irradiate tumor tissue with high doses.
Indications: Localized, small-sized tumors without lymph node or blood metastasis
Recommendations of ICRU Report No. 38
In addition to determining the target area and treatment area, ICRU also defines the concept of reference area, that is, the range of the reference isometric breadth should include most of the uterine body, the entire cervix, parametrial tissue and the upper 1/3 of the vagina.
The reference volume is determined by the length (dl) width (dw) height (dh) of the dose distribution response
Define rectal dose reference point (R), bladder dose reference point (BL)
Step Source Dosimetry Method
The irradiation time of each dwell position is no longer equal, but is lower in the middle and longer on the periphery, so that the reference points arranged in series along the longitudinal direction can obtain approximately the same dose.
The active length not only does not need to exceed the length of the target area, but is even shorter than the length of the target area (generally al=l-1.0cm)
In-tube radiation dosimetry
In-tube irradiation is mostly a single-tube irradiation dose reference point set at a certain depth under the mucosa.
The reference point dose rate is RD, which is the minimum target dose, and the hyperdose zone (HD) is the range where the received dose is greater than or equal to 2RD.
The ratio of the radius of the excess dose zone to the distance from the radiation source to the reference point is approximately 0.6
Indications for intratubular irradiation
Advantages: fast dose drop, low dose to normal tissue
Disadvantages: The treatment range of a single source is limited, and it is not suitable for cases with wider invasion.
After-loading radiotherapy process and seed implantation
After-installation
After-installation features
Unity
An iridium-192 radioactive source treats channels 1-18, and the metering calculation is accurate
Computerization
All have computer-controlled treatment planning systems and machine control systems
Multifunction
Possible intraductal, luminal and inter-tissue irradiation
High security
The radioactive source is sealed in a sealed tank and has an interlocking emergency stop device.
brachytherapy
3D image is used to determine the basic target volume
3d treatment plan design
Dose optimization in three dimensions
Dvh analysis
Afterloading radiotherapy implementation process
Disinfection and preparation
Implantation of the applicator
Grimlock
Not long, not short, not moving
CT scan
design plan
Reference point optimization
Define the dwell time difference between adjacent dwell points through a linear equation to make the reference point dose as close as possible to the given prescription dose value.
Distance/Volume Optimization
Distance optimization or volume optimization can be used during multi-tube treatment to realize optimization that relies on the mutual layout of the treatment tubes and the mutual distance of the residence points, which can significantly improve the uniformity of dose distribution.
Use the connecting pipe to connect the rear installation machine and the source applicator (takeover)
source treatment
Adjuvant external beam therapy
pilot method
Brachytherapy is first used and then external radiation is used. It is often used for intraoperative catheter placement and postoperative radiotherapy.
interpolation
In the routine external radiation therapy course, brachytherapy interspersed with once a week is commonly used for cervical cancer, vaginal cancer, rectal cancer, etc.
Extrapolation
After conventional radiotherapy, brachytherapy is added to increase the local tumor irradiation dose. It is often used for patients who have unsatisfactory or residual lesions after external beam radiotherapy.
dose effect
Low dose rate irradiation 0.4-2Gy/h
At present, traditional low-dose rate irradiation in China has been basically replaced by high-dose rate treatment.
medium dose rate irradiation
High dose rate irradiation>12Gy/h
advantage
Short treatment time
Reduces mobility inconvenience and enables treatment without hospitalization
The applicator is easy to fix in a short time
It can treat more patients in the same time, which is more beneficial for situations where many patients are in urgent need of treatment.
shortcoming
As the dose rate increases, the magnitude of late effects in normal tissue increases > the probability of tumor control increases
The dose rate is reduced, and the late effects of normal tissue are reduced > the probability of tumor control is reduced.
High dose rates reduce the therapeutic gain ratio (the ratio of the probability of tumor control to the probability of normal tissue complications)
Change treatment model
Such as using pulse metering rate therapy
Fractionated high-dose treatment
The application of fractionated irradiation is more successful, especially for cervical cancer
Cervical cancer brachytherapy has rich clinical data for easy comparison
Anatomical location characteristics, high tolerance of normal tissues around the cervix
Further research is needed on the possible damage caused by high dose rate treatment of tumors in other locations.
particle implantation
Characteristics of particle radiation
Length 4.5mm, diameter 0.8mm, measurement 0.4~0.8mci
Characteristics of iodine-125 particle radiation
Emit r-rays
Will not be absorbed into the blood
Half-life 59.6 days
Tissue penetration distance 1.7cm
low energy nuclide
As the distance between the radioactive source increases, the radiation decreases (when the quantity is the same) (2~4cm away from the radioactive source, try to reduce it by 80%~93%)
As the number of particles increases, the radiation increases (when the distance is the same)
The particle time increases and the radiation decreases (undetectable for 6 months)
Comparison of commonly used nuclide energies
99mTC(ETC)
Energy 140 Kev
131I (Treatment of Thyroid Cancer)
Energy 384kev
18F(PET-CT)
Energy 511kev
125I (particle implantation)
Energy 27kev
Particle implantation treatment and clinical characteristics
particle implant treatment
Design plan using computer three-dimensional planning system (TPS)
Patient position fixation method
The location and range of the target area and organs at risk
Description of the cure dose and crisis tolerance dose in the target area
Spatial distribution of radioactive particles in tumors and feasible puncture paths
Configuration parameters of radioactive particles, such as model, activity, quantity, etc.
Related evaluation graphics include isodose, curve distribution diagram, dvh diagram
Under the guidance of modern imaging technology (Ct), radioactive seeds (iodine-125) are implanted into the tumor
interventional needle
particle gun
Kill tumors with radiation
Clinical characteristics of particle implantation
external radiotherapy
Fractionated irradiation (about 30 times)
Treatment time (approximately 6 weeks)
High requirements for venue equipment
Planning and design takes a long time (3~4 working days)
high cost
particle implantation
one-time implant
1~2 days treatment time
Low site equipment requirements
Time consuming (a few hours)
low cost
Indications for iodine-125 seed implantation treatment
Local malignant tumor, diameter <6cm, solid lesion
Untreated primary tumors, such as prostate cancer
Tumors that require preservation of important functional organs, such as deep brain tumors
Inoperable primary tumors, such as liver cancer and nasopharyngeal cancer
In cases where external radiation is not effective, it may be used as a supplement to local dose
Residual tumor during surgery or the resection margin is too close to the tumor
Respiratory treatment for advanced tumors with severe local symptoms to relieve symptoms and improve quality of life
Contraindications to seed implantation
Those whose survival period does not exceed three months
Cachexia, poor general condition, unable to tolerate seed implantation treatment
Use with caution on hollow organs
Lymphatic drainage areas are not used for prophylactic implantation
severe diabetes
It is estimated that vital organs may be exposed to doses exceeding tolerable levels
Particle implantation protection management
Preoperative
Titanium alloy packaging (sealed seed source)
Put into lead can
There is a type A mark on the packaging surface
Special person for safekeeping
intraoperatively
Use long-handled tweezers with the particle gun pointed toward the ground (distance increases)
The speed of implanting particles needs to be fast (time is reduced)
Wear protective items: lead scarf, lead clothing, protective glasses, lead gloves, etc. (shielding) (0.25mmPb protective clothing can shield 90%~99% of the radiation dose of iodine-125 particle radioactive source)
Use contamination to detect stray particles on work surfaces and floors
After surgery
Time protection: the simplest
Distance protection: The dose rate to which the human body is exposed is approximately inversely proportional to the square of the distance, that is, if the distance is doubled, the dose rate will be reduced to 1/4 of the original (most effective)
Shielding protection: Set up appropriate protective barriers between people and radioactive sources to shield the human body from radiation exposure caused by radioactive sources (the most fundamental)