|March 26, 2016|
Brachytherapy (from the Greek word brachys , meaning "short-distance"), also known as internal radiotherapy , sealed source radiotherapy , curietherapy or endocurietherapy , is a form of radiotherapy where a radiation source is placed inside or next to the area requiring treatment. Brachytherapy is commonly used as an effective treatment for cervical ,
and skin cancer
Brachytherapy can be used alone or in combination with other therapies such as surgery, External Beam Radiotherapy (EBRT) and chemotherapy.
In contrast to EBRT in which high-energy x-rays are directed at the tumour from outside the body, brachytherapy involves the precise placement of radiation sources directly at the site of the cancerous tumour.
A key feature of brachytherapy is that the irradiation only affects a very localized area around the radiation sources. Exposure to radiation of healthy tissues further away from the sources is therefore reduced. In addition, if the patient moves or if there is any movement of the tumour within the body during treatment, the radiation sources retain their correct position in relation to the tumour. These characteristics of brachytherapy provide advantages over EBRT - the tumour can be treated with very high doses of localised radiation, whilst reducing the probability of unnecessary damage to surrounding healthy tissues.
A course of brachytherapy can be completed in less time than other radiotherapy techniques. This can help reduce the chance of surviving cancer cells dividing and growing in the intervals between each radiotherapy dose.
These features of brachytherapy reflect that most patients are able to tolerate the brachytherapy procedure very well.
Brachytherapy represents an effective treatment option for many types of cancer. Treatment results have demonstrated that the cancer cure rates of brachytherapy are either comparable to surgery and EBRT, or are improved when used in combination with these techniques.
Brachytherapy dates back to 1901 (shortly after the discovery of radioactivity by Becquerel in 1896) when Pierre Curie suggested to Henri-Alexandre Danlos that a radioactive source could be inserted into a tumour.
It was found that the radiation caused the tumour to shrink. Independently, Alexander Graham Bell also suggested the use of radiation in this way. In the early twentieth century, techniques for the application of brachytherapy were pioneered at the Curie institute in Paris by Danlos and at St Luke's and Memorial Hospital in New York by Robert Abbe.
Following initial interest in brachytherapy in Europe and the US, its use declined in the middle of the twentieth century due to the problem of radiation exposure to operators from the manual application of the radioactive sources.
However, the development of remote afterloading systems , which allow the radiation to be delivered from a shielded safe, and the use of new radioactive sources in the 1950s and 1960s, reduced the risk of unnecessary radiation exposure to the operator and patients.
This, together with more recent advancements in three dimensional imaging modalities, computerised treatment planning systems and delivery equipment has made brachytherapy a safe and effective treatment for many types of cancer today.
Different types of brachytherapy can be defined according to (1) the placement of the radiation sources in the target treatment area, (2) the rate or ???intensity??? of the irradiation dose delivered to the tumour, and (3) the duration of dose delivery .
The two main types of brachytherapy treatment in terms of the placement of the radioactive source are interstitial and contact .
The dose rate of brachytherapy refers to the level or ???intensity??? with which the radiation is delivered to the surrounding medium and is expressed in Grays per hour (Gy/h).
and prostate cancer
breasts Most HDR treatments are performed on an outpatient basis, but this is dependent on the treatment site.
Duration of dose delivery
The placement of radiation sources in the target area can be temporary or permanent .
Permanent brachytherapy is most commonly used in the treatment of prostate cancer.
Brachytherapy is commonly used to treat cancers of the cervix, and skin.
Brachytherapy can also be used in the treatment of tumours of the brain,
and soft tissues.
As the radiation sources can be precisely positioned at the tumour treatment site, brachytherapy enables a high dose of radiation to be applied to a small area. Furthermore, because the radiation sources are placed in or next to the target tumour, the sources maintain their position in relation to the tumour when the patient moves of if there is any movement of the tumour within the body. Therefore, the radiation sources remain accurately targeted. This enables clinicians to achieve a high level of dose conformity ??? i.e. ensuring the whole of the tumour receives an optimal level of radiation. It also reduces the risk of damage to healthy tissue, organs or structures around the tumour, thus enhancing the chance of cure and preservation of organ function.
Many brachytherapy procedures are performed on an outpatient basis. This convenience may be particularly relevant for patients who have to work, older patients, or patients who live some distance from treatment centres, to ensure that they have access to radiotherapy treatment and adhere to treatment plans. Shorter treatment times and outpatient procedures can also help improve the efficiency of radiotherapy clinics.
Brachytherapy can be used with the aim of curing the cancer in cases of small or locally advanced tumours, provided the cancer has not metastasized (spread to other parts of the body). In appropriately selected cases, brachytherapy for primary tumours often represents a comparable approach to surgery, achieving the same probability of cure and with similar side effects.
However, in locally advanced tumours, surgery may not routinely provide the best chance of cure and is often not technically feasible to perform. In these cases radiotherapy, including brachytherapy, offers the only chance of cure.
In more advanced disease stages, brachytherapy can be used as palliative treatment for symptom relief from pain and bleeding.
In cases where the tumour is not easily accessible or is too large to ensure an optimal distribution of irradiation to the treatment area, brachytherapy can be combined with other treatments, such as EBRT and/or surgery. Combination therapy of brachytherapy exclusively with chemotherapy is rare.
Used in combination with EBRT, brachytherapy can provide better outcomes than EBRT alone.
However, a key advantage of HDR treatment is that each dose can be delivered on an outpatient basis with a short administration time providing greater convenience for many patients.
Brachytherapy to treat prostate cancer can be given either as permanent LDR seed implantation or as temporary HDR brachytherapy.
Permanent seed implantation is suitable for patients with a localised tumour and good prognosis
and has been shown to be a highly effective treatment to prevent the cancer from returning. The procedure can be completed quickly and patients are usually able to go home on the same day of treatment and return to normal activities after 1 to 2 days.
Permanent seed implantation is often a less invasive treatment option compared to the surgical removal of the prostate.
Temporary HDR brachytherapy is a newer approach to treating prostate cancer, but is currently less common than seed implantation. It is predominately used as to provide an extra dose in addition to EBRT (known as ??????boost??? therapy) as it offers an alternative method to deliver a high dose of radiation therapy that conforms to the shape of the tumour within the prostate, while sparing radiation exposure to surrounding tissues.
Brachytherapy to treat breast cancer is usually performed with HDR temporary brachytherapy. Post surgery, breast brachytherapy can be used as a ???boost??? following irradiation of the whole breast using EBRT.
More recently, brachytherapy alone is applied in a technique called APBI (accelerated partial breast irradiation), involving delivery of radiation to only the immediate region surrounding the original tumour.
The main benefit of breast brachytherapy compared to EBRT is that a high dose of radiation can be precisely applied to the tumour while sparing radiation to healthy breast tissues and underlying structures such as the ribs and lungs. APBI can typically be completed over the course of a week.
There are two methods that can be used to deliver breast brachytherapy:
Interstitial breast brachytherapy involves the temporary placement of several flexible plastic catheters in the breast tissue. These are carefully positioned to allow optimal targeting of radiation to the treatment area while sparing the surrounding breast tissue.
Intracavitary breast brachytherapy (also known as ???balloon brachytherapy???) involves the placement of a single catheter into the breast cavity left after the removal of the tumour (lumpectomy).
There are also devices that combine the features of interstitial and intracavitary breast brachytherapy (e.g. SAVI). These devices use multiple catheters but are inserted through a single-entry point in the breast. Studies suggest the use of multiple catheters enables physicians to target the radiation more precisely.
HDR brachytherapy for nonmelanomatous skin cancer, such as basal cell carcinoma and squamous cell carcinoma, provides an alternative treatment option to surgery. This is especially relevant for cancers on the nose, ears, eyelids or lips, where surgery may cause disfigurement or require extensive reconstruction. Various applicators can be used to ensure close contact between the radiation source(s) and the skin, which conform to the curvature of the skin and help ensure precision delivery of the optimal irradiation dose.
Brachytherapy for skin cancer provides good cosmetic results and clinical efficacy; studies with up to 5 years follow-up have shown that brachytherapy is highly effective in terms local control, and is comparable to EBRT.
It has been suggested that brachytherapy may become a standard of treatment for skin cancer in the near future.
The likelihood and nature of potential acute, sub-acute or long-term side-effects associated with brachytherapy depends on the location of the tumour being treated and the type of brachytherapy being used.
Acute side effects associated with brachytherapy include localised bruising, swelling, bleeding, discharge or discomfort within the implanted region. These usually resolve within a few days following completion of treatment.
Transient increased bowel frequency, diarrhoea, constipation or minor rectal bleeding, may also occur. Acute and subacute side effects usually resolve over a matter of days or a few weeks. In the case of permanent (seed) brachytherapy for prostate cancer, there is a small chance that some seeds may migrate out of the treatment region into the bladder or urethra and be passed in the urine.
Brachytherapy for skin cancer may result in a shedding of the outer layers of skin (desquamation) around the area of treatment in the weeks following therapy, which typically heals in 5???8 weeks. If the cancer is located on the lip, ulceration may occur as a result of brachytherapy, but usually resolves after 4???6 weeks.
Most of the acute side effects associated with brachytherapy can be treated with medication or through dietary changes, and usually disappear over time (typically a matter of weeks), once the treatment is completed. The acute side effects of HDR brachytherapy are broadly similar to EBRT.
In a small number of people, brachytherapy may cause long-term side effects due to damage or disruption of adjacent tissues or organs. Long-term side effects are usually mild or moderate in nature. For example, urinary and digestive problems may persist as a result of brachytherapy for cervical or prostate cancer, and may require ongoing management.
Brachytherapy for prostate cancer may cause erectile dysfunction in approximately 15-30% of patients.
Brachytherapy for breast or skin cancer may cause scar tissue to form around the treatment area. In the case of breast brachytherapy, fat necrosis may occur as a result of fatty acids entering the breast tissues. This can cause the breast tissue to become swollen and tender. Fat necrosis is a benign condition and typically occurs 4???12 months after treatment and affects about 2% of patients.
Patients often ask if they need to have special safety precautions around family and friends after receiving brachytherapy. If temporary brachytherapy is used, no radioactive sources remain in the body after treatment. Therefore, there is no radiation risk to friends or family from being in close proximity with them.
If permanent brachytherapy is used, low dose radioactive sources (seeds) are left in the body after treatment - the radiation levels are very low and decrease over time. In addition, the irradiation only affects tissues within a few millimeters of the radioactive sources (i.e. the tumour being treated). As a precaution, some people receiving permanent brachytherapy may be advised to not hold any small children or be too close to pregnant women for a short time after treatment. Radiation oncologists or nurses can provide specific instructions to patients and advise for how long they need to be careful.
In order to accurately plan the brachytherapy procedure, a thorough clinical examination is performed to understand the characteristics of the tumour. In addition, a range of imaging modalities can be used to visualise the shape and size of the tumour and its relation to surrounding tissues and organs. These include x-ray radiography, ultrasound, computed axial tomography (CT or CAT) scans and magnetic resonance imaging (MRI).
The data from many of these sources can be used to create a 3D visualisation of the tumour and the surrounding tissues.
Using this information, a plan of the optimal distribution of the radiation sources can be developed. This includes consideration of how the source carriers (applicators), which are used to deliver the radiation to the treatment site, should be placed and positioned. Applicators are non-radioactive and are typically needles or plastic catheters. The specific type of applicator used will depend on the type of cancer being treated and the characteristics of the target tumour.
This initial planning helps to ensure that ???cold spots??? (too little irradiation) and ???hot spots??? (too much irradiation) are avoided during treatment, as these can respectively result in treatment failure and side-effects.
Insertion and imaging of the applicator(s)
Before radioactive sources can be delivered to the tumour site, the applicators have to be inserted and correctly positioned in line with the initial planning.
Imaging techniques, such as x-ray, fluoroscopy and ultrasound are typically used to help guide the placement of the applicators to their correct positions and to further refine the treatment plan. CAT scans and MRI can also be used. Once the applicators are inserted, they are held in place against the skin using sutures or adhesive tape to prevent them from moving. Once the applicators are confirmed as being in the correct position, further imaging can be performed to guide detailed treatment planning.
Creation of a virtual patient
The images of the patient with the applicators in situ are imported into treatment planning software and the patient is brought into a dedicated shielded room for treatment. The treatment planning software enables multiple 2D images of the treatment site to be translated into a 3D ???virtual patient???, within which the position of the applicators can be defined. The spatial relationships between the applicators, the treatment site and the surrounding healthy tissues within this ???virtual patient??? are a copy of the relationships in the actual patient.
Optimizing the irradiation plan
To identify the optimal spatial and temporal distribution of radiation sources within the applicators of the implanted tissue or cavity, the treatment planning software allows virtual radiation sources to be placed within the virtual patient. The software shows a graphical representation of the distribution of the irradiation. This serves as a guide for the brachytherapy team to refine the distribution of the sources and provide a treatment plan that is optimally tailored to the anatomy of each patient before actual delivery of the irradiation begins.
This approach is sometimes called ???dose-painting???.
The radiation sources used for brachytherapy are always enclosed within a non-radioactive capsule. The sources can be delivered manually, but are more commonly delivered through a technique known as ???afterloading???.
Manual delivery of brachytherapy is limited to a few LDR applications, due to risk of radiation exposure to clinical staff.
In contrast, afterloading involves the accurate positioning of non-radioactive applicators in the treatment site, which are subsequently loaded with the radiation sources. In manual afterloading, the source is delivered into the applicator by the operator.
Remote afterloading systems provide protection from radiation exposure to healthcare professionals by securing the radiation source in a shielded safe. Once the applicators are correctly positioned in the patient, they are connected to an ???afterloader??? machine (containing the radioactive sources) through a series of connecting guide tubes. The treatment plan is sent to the afterloader, which then controls the delivery of the sources along the guide tubes into the pre-specified positions within the applicator. This process is only engaged once staff are removed from the treatment room. The sources remain in place for a pre-specified length of time, again following the treatment plan, following which they are returned along the tubes to the afterloader.
On completion of delivery of the radioactive sources, the applicators are carefully removed from the body. Patients typically recover quickly from the brachytherapy procedure, enabling it to often be performed on an outpatient basis.
Commonly used radiation sources (radionuclides) for brachytherapy
Electronic brachytherapy involves placement of miniature low energy x-ray tube sources into a pre-positioned applicator within body/tumour cavities to rapidly deliver high doses to target tissues while maintaining low doses to distant non-target tissues.
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