Brachytherapy - WikiHQ

Brachytherapy is a form of radiation therapy where a sealed radiation source is placed inside or next to the area requiring treatment. The word "brachytherapy" comes from the Greek word , meaning "short-distance" or "short". Brachytherapy is commonly used as an effective treatment for cervical, prostate, breast, esophageal and skin cancer and can also be used to treat tumours in many other body sites. Treatment results have demonstrated that the cancer-cure rates of brachytherapy are either comparable to surgery and external beam radiotherapy (EBRT) or are improved when used in combination with these techniques. Brachytherapy can be used alone such as in early prostate cancer or in combination with other therapies such as surgery, EBRT and chemotherapy such as in advanced cervical cancer

Brachytherapy contrasts with unsealed source radiotherapy, in which a therapeutic radionuclide (radioisotope) is injected into the body to chemically localize to the tissue requiring destruction. It also contrasts to External Beam Radiation Therapy (EBRT), in which high-energy x-rays (or occasionally gamma-rays from a radioisotope like cobalt-60) are directed at the tumour from outside the body. Brachytherapy instead involves the precise placement of short-range radiation-sources (radioisotopes, iodine-125 or caesium-131 for instance) directly at the site of the cancerous tumour. These are enclosed in a protective capsule or wire, which allows the ionizing radiation to escape to treat and kill surrounding tissue but prevents the charge of radioisotope from moving or dissolving in body fluids. The capsule may be removed later, or (with some radioisotopes) it may be allowed to remain in place.

A feature of brachytherapy is that the irradiation affects only a very localized area around the radiation sources. Exposure to radiation of healthy tissues farther 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. These features of brachytherapy mean that most patients are able to tolerate the brachytherapy procedure very well.

The global market for brachytherapy reached US$680 million in 2013, of which the high-dose rate (HDR) and LDR segments accounted for 70%. Microspheres and electronic brachytherapy comprised the remaining 30%. One analysis predicts that the brachytherapy market may reach over US$2.4 billion in 2030, growing by 8% annually, mainly driven by the microspheres market as well as electronic brachytherapy, which is gaining significant interest worldwide as a user-friendly technology.

Medical uses

thumb|upright=1.5|Body sites in which brachytherapy can be used to treat cancer

Brachytherapy is commonly used to treat cancers of the cervix, prostate, breast, and skin. urinary tract (bladder, urethra, penis), female reproductive tract (uterus, vagina, vulva), and soft tissues.

Patients receiving brachytherapy generally have to make fewer visits for radiotherapy compared with EBRT, and overall radiotherapy treatment plans can be completed in less time.

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.

Cervical cancer

Brachytherapy is commonly used in the treatment of early or locally confined cervical cancer and is a standard of care in many countries.

Cervical cancer can be treated with either LDR, PDR or HDR brachytherapy.

Used in combination with EBRT, brachytherapy can provide better outcomes than EBRT alone.

The chances of staying free of disease (disease-free survival) and of staying alive (overall survival) are similar for LDR, PDR and HDR treatments.

However, a key advantage of HDR treatment is that each dose can be delivered on an outpatient basis with a short administration time

Prostate cancer

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 survival rate is similar to that found with EBRT or surgery (radical prostatectomy), but with fewer side effects such as impotence and incontinence. 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 one to two days.

Permanent seed implantation is often a less invasive treatment option compared to the surgical removal of the prostate.

HDR brachytherapy as a boost for prostate cancer also means that the EBRT course can be shorter than when EBRT is used alone.

Brachytherapy can be used after surgery, before chemotherapy or palliatively in the case of advanced disease. Brachytherapy to treat breast cancer is usually performed with HDR temporary brachytherapy. Post surgery, breast brachytherapy can be used as a "boost" following whole breast irradiation (WBI) using EBRT.

More recently, brachytherapy alone is used to deliver 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 whole breast irradiation 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. An applicator is placed in the cavity left after tumour removal and a mobile electronic device generates radiation (either x-rays) and delivers it via the applicator. Radiation is delivered all at once and the applicator removed before closing the incision.

Intracavitary breast brachytherapy

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.

Permanent breast seed implantation

Permanent breast seed implantation (PBSI) implants many radioactive "seeds" (small pellets) into the breast in the area surrounding the site of the tumour, similar to permanent seed prostate brachytherapy. The seeds are implanted in a single 1–2 hour procedure and deliver radiation over the following months as the radioactive material inside them decays. Risk of radiation from the implants to others (e.g. partner/spouse) has been studied and found to be safe.

In a clinical study, GammaTile Therapy improved local tumor control compared to previous same-site treatments without an increased risk of side effects.

Esophageal cancer

For esophageal cancer radiation treatment, brachytherapy is one option for effective treatment, involves definitive radiotherapy (boost) or palliative treatments. Definitive radiotherapy (boost) can deliver the dose precisely and palliative treatments can be given to relieve dysphagia. The large diameter applicators or balloon type catheter are used with the afterloader to expand the esophagus and facilitate the delivery of radiation dose to tumor with sparing of nearby normal tissue.

Brachytherapy followed EBRT or surgery have been shown to improve the survival rate and local recurrent rate than EBRT or surgery only for esophageal cancer patients.

Brachytherapy for skin cancer provides good cosmetic results and clinical efficacy; studies with up to five years follow-up have shown that brachytherapy is highly effective in terms of local control, and is comparable to EBRT. Treatment times are typically short, providing convenience for patients.

It has been suggested that brachytherapy may become a standard of treatment for skin cancer in the near future.

In treating In-stent restenosis (ISR) Drug Eluting stents (DES) have been found to be superior to Intracoronary Brachytherapy (ICBT).<!-- and considered for the treatment of atrial fibrillation.

Side effects

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

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.

Patients may also feel fatigued for a short period following treatment.

Brachytherapy treatment for cervical or prostate cancer can cause acute and transient urinary symptoms such as urinary retention, urinary incontinence or painful urination (dysuria).

Transient increased bowel frequency, diarrhoea, constipation or minor rectal bleeding may also occur.

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. Vaginal brachytherapy targets gynecological malignancies with minimal impact to nearby organs and lymph nodes while pelvic external beam radiation targets the malignancy using a wider radiation field that traverses more of the lymphatic system, increasing the risk of lymphatic fibrotic proximal pressure and mechanical insufficiency.

Brachytherapy for prostate cancer may cause erectile dysfunction in approximately 15–30% of patients.

Safety around others

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 millimetres of the radioactive sources (i.e. the tumour being treated). As a precaution, some people receiving permanent brachytherapy may be advised not to 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.

Dose rate

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).

Low-dose rate (LDR) brachytherapy involves implanting radiation sources that emit radiation at a rate of up to 2 Gy·h−1. LDR brachytherapy is commonly used for cancers of the oral cavity, oropharynx,

Medium-dose rate (MDR) brachytherapy is characterized by a medium rate of dose delivery, ranging between 2 Gy·h−1 to 12 Gy·h−1.

Pulsed-dose rate (PDR) brachytherapy involves short pulses of radiation, typically once an hour, to simulate the overall rate and effectiveness of LDR treatment. Typical tumour sites treated by PDR brachytherapy are gynaecological For the geometry in figure 1, this formalism uses five parameters.

Strength of the source: How much radiation is being emitted by the seed, expressed as air kerma strength and denoted by <math>S_k</math>.
Dose rate of the source: How much dose the seed will deliver to the reference point over a certain period of time, denoted by <math>\Lambda</math>.
Geometry factor: How the shape of the seed will affect the dose at points away from the reference point, denoted by <math>G(r,\theta)</math>.
Anisotropy function: How the much radiation will be stopped before passing out of the seed, denoted by <math>F(r,\theta)</math>.
Radial dose function: How the radiation will interact with the material surrounding the seed, denoted by <math>g(r)</math>.

The equation which links these parameters is, <math>D(r,\theta)=S_k \Lambda \frac{G(r,\theta)}{G(r_0,\theta_0)}g(r)F(r,\theta)</math>

Duration of dose delivery

The placement of radiation sources in the target area can be temporary or permanent.

Temporary brachytherapy involves placement of radiation sources for a set duration (usually a number of minutes or hours) before being withdrawn.

Permanent brachytherapy, also known as seed implantation, involves placing small LDR radioactive seeds or pellets (about the size of a grain of rice) in the tumour or treatment site and leaving them there permanently to gradually decay. Over a period of weeks or months, the level of radiation emitted by the sources will decline to almost zero. The inactive seeds then remain in the treatment site with no lasting effect. Permanent brachytherapy is most commonly used in the treatment of prostate cancer. This approach is sometimes called 'dose-painting'.

Treatment delivery

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.

Radiation sources

Commonly used radiation sources (radionuclides) for brachytherapy include:

{| class="wikitable"

! Radionuclide

! Decay mode

! Half-life

! Energy

| Caesium-131 (131Cs)

| ε

| 9.7 days

| 30.4 keV (mean)

| Caesium-137 (137Cs)

| β−, γ

| 30.17 years

| 0.512, 0.662 MeV γ-rays

| Cobalt-60 (60Co)

| β−, γ

| 5.26 years

| 1.17, 1.33 MeV γ-rays

| Iridium-192 (192Ir)

| β−, ε, γ

| 73.8 days

| 0.38 MeV (mean)

| Iodine-125 (125I)

| ε

| 59.6 days

| 27.4, 31.4 and 35.5 keV

| Palladium-103 (103Pd)

| ε

| 17.0 days

| 21 keV (mean)

| Ruthenium-106 (106Ru)

| β−

| 1.02 years

| 3.54 MeV

| Radium-226 (226Ra)

| α

| 1599 years

History

Brachytherapy dates back to 1901 (shortly after the discovery of radioactivity by Henri 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.

Duane returned to the United States in 1913 and worked in a joint role as assistant professor of physics at Harvard and Research Fellow in Physics of the Harvard Cancer Commission. The Cancer Commission was founded in 1901 and hired Duane to investigate the usage of radium emanations in the treatment of cancer. In 1915 he built Boston's first "radium cow" and thousands of patients were treated with the radon-222 generated from it.

Interstitial radium therapy was common in the 1930s. until at least 1958. Gold shells were selected by Gino Failla around 1920 to shield beta rays while passing gamma rays. Cobalt needles were also used briefly after World War II. 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.

The second occurred in Prague, sometime before 2011. In September of that year a computer scientist named Pavel Bykov, who happened to have a small geiger counter built into his wristwatch, noticed abnormal readings in the Podolí neighborhood playground where he had taken his children. After retrieving a larger counter from his home, Bykov determined that a highly radioactive source was buried in the playground. The park was evacuated by authorities soon after. Specialized excavation equipment recovered a 20 x 2mm radium-226 needle from the playground's dirt. The source remained highly radioactive, emitting 500 μSv per hour from a meter away. At that distance the needle gave a per-hour dose equivalent to one year of background exposure.

References

External links

American Brachytherapy Society (ABS)