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Encyclopedia > Brachytherapy
Brachytherapy for prostate cancer is administered using "seeds," small radioactive rods implanted directly into the tumour.

Brachytherapy, also known as sealed source radiotherapy or endocurietherapy, is a form of radiotherapy where a radioactive source is placed inside or next to the area requiring treatment. Conversely, external beam radiotherapy, or teletherapy, is the application of radiation that has been externally produced by a linear accelerator. Brachytherapy is commonly used to treat localized prostate cancer[1] and cancers of the head and neck.[2] Image File history File linksMetadata Brachytherapy. ... Image File history File linksMetadata Brachytherapy. ... Radiation therapy (or radiotherapy) is the medical use of ionizing radiation as part of cancer treatment to control malignant cells (not to be confused with radiology, the use of radiation in medical imaging and diagnosis). ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ... External beam radiotherapy otherwise known as teletherapy, is the most frequently used form of radiotherapy. ... A Linear particle accelerator is an electrical device for the acceleration of subatomic particles. ... Prostate cancer is a disease in which cancer develops in the prostate, a gland in the male reproductive system. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... Human Head redirects here. ... A human neck. ...


Brachy is from a Greek word for "short", so brachytherapy roughly translated is short distance therapy.


Brachytherapy can be split into four main types:

  • Mold brachytherapy. Superficial tumours can be treated using sealed sources placed close to the skin. Dosimetry is often performed with reference to the Manchester system; a rule-based approach designed to ensure that the dose to all parts of the target volume is within 10% of the prescription dose.
  • Surface Applicator is usually called Strontium plaque therapy and is used for very superficial lesions less than 1 mm thick. The plaque is a hollow, thin silver casing that encloses a radioactive Strontium-90 powdered salt. The beta (electron) particles produced from Strontium's radioactive decay have a very shallow penetration. Typically the Sr90 plaque is placed on the bed of a resected pterygium. A stat dose of around 10-12 Gy is delivered by timing the contact. As the electrons only penetrate a few mm of air, radiation protection issues are slightly less but very different to other radiation sources. Cleaning the plaques that are placed on the eye sclera is required but must be gentle because the silver casing is thin and easily damaged. Strontium belongs to the same chemical class as Calcium, i.e., an alkaline earth metal, and so will co-locate in the bone if any strontium salt makes contact with the eye and is absorbed. Operators can prevent exposure to the beta rays by holding the applicator to face away from their bodies.
  • Interstitial brachytherapy. Here the sources are inserted into tissue. The first treatments of this kind used needles containing Radium-226, arranged according to the Manchester system, but modern methods tend to use Iridium-192 wire. Iridium wire can be arranged either using the Manchester or the Paris system; the latter was designed specifically to take advantage of the new nuclide. Prostate cancer treatment with Iodine-125 seeds is also classified as interstitial brachytherapy. For details of the gamma emitters please see commonly used gamma emitting isotopes.
  • Intracavitary brachytherapy places the sources inside a pre-existing body cavity. The most common applications of this method are gynaecological in nature, although it can also be performed on the nasopharynx.
  • Intravascular brachytherapy places a catheter with the sources inside the vasculature. The most common application of this method is the treatment of coronary in-stent restenosis, although the therapy has also been investigated for use in the treatment of peripheral vasculature stenoses.

Contents

Dosimetry is the measurement of absorbed dose in matter and tissue resulting from the exposure to ionizing radiations. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Atomic mass 87. ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Standard atomic weight 107. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Atomic mass 87. ... e- redirects here. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Atomic mass 87. ... A pterygium, meaning wing, is a benign growth of the conjunctiva. ... Schematic diagram of the human eye. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Atomic mass 87. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... The alkaline earth metals are the series of elements in Group 2 (IUPAC style) of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra) (not always considered due to its radioactivity and very short half-life). ... General Name, Symbol, Number radium, Ra, 88 Chemical series alkaline earth metals Group, Period, Block 2, 7, s Appearance silvery white metallic Standard atomic weight (226) g·mol−1 Electron configuration [Rn] 7s2 Electrons per shell 2, 8, 18, 32, 18, 8, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number iridium, Ir, 77 Chemical series transition metals Group, Period, Block 9, 6, d Appearance silvery white Atomic mass 192. ... A nuclide (from lat. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Standard atomic weight 126. ... Caesium-137 is a radioactive isotope which is formed mainly by nuclear fission. ... The shamefulness associated with the examination of female genitalia has long inhibited the science of gynaecology. ... The nasopharynx (nasal part of the pharynx) lies behind the nose and above the level of the soft palate: it differs from the oral and laryngeal parts of the pharynx in that its cavity always remains patent (open). ...

Remote and Manual Afterloading Machines

Afterloading Machines as they are called are the machines that perform brachytherapy treatments.


Manual Afterloading Machines

In the early days of brachytherapy (ca. 1920), the only way to place the radioactive material into the hollow tubes or hollow body cavities was for someone to carry the source up to the patient's bedside (room or operating theater) in a safe, take it out and place it inside the hollow destination. By necessity, the staff member (usually the doctor) undertaking this received some radiation dose. This was manual loading.


In cases such as cervix brachytherapy where a Heyman capsule was used, radiation exposure from manual loading could be appreciable as all the sources had to be placed individually while the patient was anaesthetized on the operating bed. It was not long before the doctors who were exposed reasoned that their exposure could be lessened by placing metal tubes first, and then placing the radioactive sources inside metal tubes at a later time. The metal tubes allowed the development of standard sizing and strength sources so that source numbers could be calculated first, and then prepared to facilitate a single step procedure to manually afterload.


Manual afterloading machines could not be activated from outside the room, as the source had to be manually inserted. The source would have been prepared in a hot lab as a source train and inserted in a theater or ward. The source could not be unloaded for nursing visits.


Remote Afterloading Machines

Although manual afterloading reduced exposures, the guiding principle of radiation protection is to keep exposures as low as reasonably achievable (ALARA) given prevailing economic, political and societal factors. The move to reduce exposures even further led to the introduction of remote afterloading. This technique relies on the use of hollow tubes which are connected to a safe containing a small radioactive source welded to a wire that is driven out by a stepping motor to predetermined positions to deliver radiation dose.


These machines deliver their treatment remotely. A plan is produced that describes the patterns of the stepping motor (distance and dwell time). The motor is only engaged when all staff have left the shielded room that holds the patient for the duration of the treatment.


This means that the nurse or therapeutic radiographer that administers can leave the room (located either in theatre or ward) and start the treatment outside. Empty catheters are placed into the patient and the 'live' source is entered at a later date. This means that the non-active dummy guides can be repositioned and checked. In other words, the source is not placed into the guides until the positioning is acceptable. The machine then runs a pneumatic drive wire through the catheters and guide wires to check that there are no obstructions and the source can safely run through the course of it. After this the check has been performed the source leaves its secure safe and the treatment begins. The development of the remote afterloading machines is a benefit to the many radiation safety issues surrounding manual afterloading machines, but they are expensive and more prone to error.


Advantages of Remote over Manual

  • No radiation exposure in patient transit
  • No exposure to theater or ward staff

HDR brachytherapy

High Dose Rate (HDR) brachytherapy is a common brachytherapy method. Applicators in the form of catheters are arranged, usually according to the Manchester or Paris system on, or in the patient. A high dose rate source (often iridium 192, Ir-192) is then driven along the catheters on the end of a wire by a machine while the patient is isolated in a room. The source dwells in a preplanned position for a preset time before stepping forward along the catheter and repeating, to build up the required dose distribution. The advantage of this treatment over implanting radioactive sources directly is that there is lower staff exposure and the source can be more active due to low staff exposure, thus making treatment times quicker.


LDR brachytherapy

Low dose rate (LDR) brachytherapy with a machine works in a similar way. Another variant is the sources being in the form of active and inactive balls which are again, driven into the patient using a machine[citation needed].


Side Effects

There are many side effects associated with brachytherapy treatment, most of these are urinary in nature and are short lived. however, between six and fifty percent of patients (depending upon the seriousness of the cancer) may become impotent following brachytherapy[citation needed]. Another side effect can occur as a consequence of migration of seeds out of the prostate; it is therefore important to filter urine so as to recover the radioactive seeds. A side-effect is any effect other than an intended primary effect. ... Impotence or, more clinically, erectile dysfunction is the inability to maintain an erection of the penis for satisfactory sexual intercourse regardless of the capability of ejaculation. ...


References

  1. Brachytherapy in New Zealand
  2. a Merrick GS, Butler WM, Wallner KE, Galbreath RW, Adamovich E (2005). "Monotherapeutic brachytherapy for clinically organ-confined prostate cancer". West Virginia Medical Journal 101 (4): 168-171. 
  3. a Mazeron JJ, Noel G, Simon JM, Racadot S, Jauffret E (2003). "Brachytherapy in head and neck cancers". Cancer Radiotherapy 7 (1): 62-72. 

External links


  Results from FactBites:
 
UCSF Radiation Oncology : Brachytherapy (1156 words)
Brachytherapy refers to a method of delivering radiation to tumors by placing radioactive sources either directly into the tumor or very close to it.
Brachytherapy also produces a highly heterogeneous dose distribution because dose around the radioactive sources is much higher than a region just a few millimeters away.
Brachytherapy is a method of delivering radiation to tumors by placing radioactive sources either within or immediately adjacent to tumor tissue.
Brachytherapy Side Effects & Personalized Cancer Treatment Options (933 words)
Brachytherapy, also known as sealed source radiotherapy and endocurietherapy, is a type of radiotherapy in which radiation is delivered inside the area requiring treatment.
Interstitial brachytherapy, in which radiation sources are inserted into the tissue itself; for example, prostate cancer brachytherapy employs the insertion of a series of tiny catheters into and around the tumor.
Brachytherapy is a form of radiation therapy that delivers the dose of radiation to the effected areas directly.
  More results at FactBites »

 
 

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